ObjectivePhotoacoustic tweezers (PATs) are a promising noninvasive technology for precise microparticle manipulation that leverage the photoacoustic effect to exert controlled forces on particles within a liquid medium. Conventional methods, such as optical and acoustic tweezers, present limitations such as potential damage to particles, inadequate spatial control, and restricted manipulation in three-dimensional (3D) environments. Hence, this study focuses on the theoretical development of a PAT model that integrates photo-thermo-acoustic-mechanical coupling effects. Using a ring-shaped laser beam, this study aims to investigate particle motion and force characteristics under various laser conditions. Additionally, this study seeks to establish a robust theoretical framework for PATs, thus filling the gaps in 3D particle manipulation and providing guidance for the optimization of experimental parameters.MethodsA multiphysics coupling model for PATs was constructed to describe the interactions among photo-thermal, acoustic, and mechanical effects in a liquid medium. The model accounts for the transformation of laser energy density into heat and the subsequent thermal expansion, and the generation of acoustic waves that induces acoustic radiation forces and acoustic streaming. A ring-shaped laser beam was employed to create spatially confined acoustic fields that can trap and manipulate particles. Using the finite-element method (FEM) in Comsol software, the model was used to simulate high-frequency pulsed laser effects, including energy transfer, thermal expansion, acoustic wave propagation, and the resultant particle dynamics. The governing equations for the coupled fields were derived by incorporating the spatial and temporal distributions of the laser, the thermal and acoustic properties of the medium, and force interactions on the particles. The acoustic radiation forces were modeled based on Gor’kov potential theory, whereas the acoustic streaming fields were calculated using nonlinear fluid-dynamics equations. Simulations were performed to analyze the effects of laser energy densities, pulse widths, and frequencies on the behavior of the system, which revealed the distributions of forces and streaming flows in 3D space. The particle motion under combined acoustic radiation and streaming forces was analyzed to elucidate the dynamics of particle trapping and manipulation.Results and DiscussionsThe simulation results provide key insights into the behavior of PATs in 3D particle manipulation, which highlight the dependence of acoustic radiation forces, Gor’kov potential, and acoustic streaming on the laser parameters. The acoustic radiation forces show significant dependence on the laser energy density, pulse width, and frequency, as illustrated in Fig. 3, where the spatial distribution around the ring-shaped laser beam is symmetrical, with the maximum forces occurring near the ring boundary. Increasing the laser energy density increases these forces, as shown in Fig. 5(a), where higher energy densities (e.g., 50 mJ·cm-2) generate forces up to 65 pN. Similarly, reducing the pulse width amplifies the radiation forces, as shown in Fig. 5(c). The Gor’kov potential wells, as depicted in Figs. 5(b) and (d), deepen with higher densities or shorter pulse widths, thereby improving particle-trapping stability. Additionally, the frequency-dependent behavior, as shown in Figs. 5(e) and (f), reveals that a frequency of 10 MHz yields the maximum forces and well-defined potential wells, thus enabling efficient particle trapping. However, as the frequency increases further, the wave attenuation significantly reduces the force and potential depth, as shown in Fig. 6.In addition to acoustic radiation forces, acoustic streaming is crucial in particle manipulation and serves as an auxiliary force. This secondary force, which is generated via nonlinear fluid interactions, is particularly effective at 10 MHz, where the streaming velocity peaks at 0.05 μm/s, as shown in Fig. 7. The streaming-flow patterns effectively stabilize particles within the trapping zones. However, as the frequency increases beyond 10 MHz, the energy density dissipation causes the streaming effect to diminish significantly, thus decreasing the velocities, as shown in Figs. 7(b)?(d). This relationship between radiation forces and streaming provides a robust mechanism for particle trapping, which is further supported by the trajectories shown in Fig. 9. The particles propagate toward the trapping zones with increasing velocity, with the maximum number recorded near the traps before a stable number is indicated within the Gor’kov potential wells. The color-coded trajectories in Fig. 9 highlight the deceleration of the particles as they approach the traps, thereby illustrating the dynamic balance between the radiation forces and streaming-induced drag.Finally, the capability of the system to manipulate particles along the Z-axis was examined, as shown in Fig. 4. Although the acoustic radiation forces in the Z-direction are weaker than those in the radial direction, the combined effect of forces and streaming provides sufficient control for effective 3D manipulation. This capability underscores the effectiveness of PATs in achieving stable particle trapping and precise manipulation. In general, these findings demonstrate that PATs are highly effective for 3D particle manipulation, particularly at moderate laser frequencies (approximately 10 MHz) and energies, where the combined effect of radiation forces and streaming ensures stability and precision. These results establish a solid foundation for the practical application of PATs in biomedicine and materials science.ConclusionsIn this study, a comprehensive theoretical framework for PATs was established via a multiphysics coupling model that integrates photo-thermo-acoustic-mechanical interactions. The findings underscore the importance of laser parameters in optimizing particle manipulation. Specifically, this study identified 10 MHz as an ideal frequency for achieving maximum acoustic radiation forces and stable Gor’kov potential wells. High laser energy densities and short pulse widths are critical for enhancing the trapping efficiency, although practical considerations, such as avoiding thermal damage, must guide parameter selection. The integration of acoustic radiation forces and streaming flows highlights the versatility of this system for 3D manipulation. Although radiation forces dominate the trapping mechanism, streaming flows provide auxiliary control, particularly for stabilizing particle trajectories. The insights obtained from this study contribute to a broader understanding of PAT mechanisms and offer practical guidelines for experimental implementation. The potential applications of PATs include targeted drug delivery, cell manipulation, and the assembly of nanostructured materials, thus highlighting their transformative potential in biomedicine and nanotechnology.

SignificanceThe rapid advancement of precision medicine has established liquid biopsy as a transformative tool for disease screening, diagnosis, and monitoring. By analyzing circulating biomarkers in bodily fluids, such as extracellular vesicles (EVs), cell-free nucleic acids, proteins, metabolites, and circulating tumor cells, liquid biopsy offers a non-invasive method for disease detection. It enables real-time monitoring of disease progression, transforming clinical diagnostics and patient management. Among the various liquid biopsy methodologies, surface plasmon resonance (SPR) stands out due to its rapid response, high sensitivity, real-time monitoring, multimodal detection capabilities, and tunable micro-nanostructures. These features demonstrate its potential to significantly enhance liquid biopsy applications and revolutionize diagnostic strategies.ProgressThis review focuses on recent advancements in SPR technology for liquid biopsy, focusing on the major biomarkers used.We first discuss the fundamental principles of four commonly used SPR technologies. SPR uses resonance phenomena occurring at the interface of metal films and dielectric mediums, enabling highly sensitive detection of biomolecular interactions. Its ability to perform label-free detection and real-time analysis makes it essential for detecting biomarkers at very low concentrations. This foundational understanding provides insights into addressing several challenges faced by liquid biopsy, such as the limited number of disease-specific markers, the complexity of biological samples, limited detection throughput, high cost, and issues related to clinical relevance. SPR addresses these challenges by integrating micro-nanostructure design, molecular probes, microfluidic chips, and sophisticated data analysis. These enhancements improve sensitivity, specificity, and detection speed while enabling multiple biomarker analyses. Such advancements promise more robust and reliable SPR-based platforms for clinical applications.A particularly promising area is the application of SPR technologies to EVs. These vesicles serve as novel circulating biomarkers, offering advantages such as stability, spatial-temporal heterogeneity, diverse molecular content, and high abundance in body fluids. We describe recent advances in designing innovative SPR platforms for detecting and analyzing EVs. These advancements provide crucial insight into the molecular characteristics of EVs, creating opportunities for improved disease diagnostics and monitoring. However, challenges such as standardizing sample processing, correlating EV markers with clinical outcomes, and addressing variability in detection signals across techniques must be overcome to define the full clinical potential of EVs. SPR’s adaptability, combined with complementary technologies, provides a promising method to overcome these challenges, maximizing the clinical usefulness of EVs.Inherent disease complexity and heterogeneity often require a comprehensive analysis of multiple biomarkers. Single-marker diagnostics may fall short of addressing these complexities. SPR multiplexing allows simultaneous detection and analysis of proteins, nucleic acids, metabolites, and tumor cells, offering a comprehensive view of disease biology. We highlight these advancements, which significantly enhance diagnostic accuracy and provide a deeper understanding of disease mechanisms.Conclusions and ProspectsLiquid biopsy is a pivotal technology for early disease diagnosis and ongoing monitoring because of its non-invasive nature and real-time monitoring capabilities. SPR, with its unique micro-nano photonic properties, offers transformative potential in enhancing liquid biopsy applications. However, several challenges must be addressed to facilitate the widespread adoption of SPR-based liquid biopsy.A primary obstacle is the low concentration of circulating biomarkers, which requires additional sample purification and enrichment for effective detection. These steps increase experimental complexity and time, impeding rapid clinical translation. Furthermore, specialized SPR platforms and detection systems involve significant costs, limiting their accessibility and use in routine medical diagnostics. Limited clinical sample sizes and a lack of standardized sample collection methods hinder the reproducibility and validation of findings. Addressing these issues will be critical to ensure the reliability and scalability of SPR technologies. Innovation in SPR materials, device configurations, and detection methods is essential to overcome these challenges. Advancements in areas such as molecular probes, rare-earth nanomaterials, metamaterials, microfluidics, and artificial intelligence can expand the capabilities of SPR systems. These innovations will enhance sensitivity, automate processes, and lower costs, making SPR more accessible for clinical and personal health applications.The growing demand for personalized medicine and home-based testing confirms the need for compact, intelligent, cost-effective SPR devices. Miniaturization and portability are essential to meet the needs of dynamic health monitoring and expand the reach of liquid biopsy technologies. Standardizing clinical protocols, ensuring the clinical relevance of biomarkers, and improving data analysis frameworks will enhance the reproducibility and translational potential of SPR-based systems. SPR-based liquid biopsy technologies can revolutionize diagnostics by solving these challenges, enabling robust, accessible, and cost-effective solutions. Integrating SPR’s optical properties with cutting-edge micro-nanotechnology and data-driven insights has set the stage for a new era in precision medicine, transforming how diseases are detected, understood, and managed.

ObjectiveNon-invasive, timely and accurate detection is of great significance for the early diagnosis and treatment of tumors. Raman spectroscopy has shown good application prospects in the field of tumor detection due to its advantages of non-destructive acquisition, high sensitivity and rapid detection. Several studies have given the principles of Raman spectroscopy for detecting cancerous tissues, however, this technique still has the limitations of weak signals and insufficient penetration depth and faces the challenge of improving its ability in detecting subcutaneous deep tumor signals for clinical applications. Spatially offset Raman spectroscopy (SORS) is a deep-penetration Raman spectroscopy, which reduces the signal interference in the surface layer in order to effectively obtain the spectral information of deep samples by physically shifting the spectral acquisition point with a certain distance laterally relative to the excitation point. However, most of the studies indicate that the detection depth of this technique in biological tissues is limited to 2 mm, far from being sufficient for the detection of deep-seated tumors, and the quantitative relationship between the detection depth and the spatial offset distance (Δd) lacks the support of experimental data. In this study, we conduct experiments based on a self-developed fiber optic Raman probe, and investigate the maximum detection depth of the fiber optic Raman probe detection technique by respectively using two acquisition modes of transmission and reflection. Based on the both modes, the SORS is introduced, and the quantitative relationship between Δd and the optimal detection depth is established. This study provides an experimental data support for the application of SORS in clinical tumor diagnosis, and provides a technical reference for the further optimization of Raman spectroscopy.MethodsRaman spectra of pork adipose tissue (PAT) are collected under various experimental conditions based on a self-developed fiber optic Raman probe. First, the experimental optical paths of transmission and reflection modes are constructed (Fig. 2), then the PAT is cut into 3 mm-thick slices, and the samples are stacked layer by layer for spectral acquisition in both transmission and reflection modes until the maximum detection depth is obtained. Then, after obtaining the detection depths in the both Raman spectral acquisition modes, the SORS is introduced, and the experiments are carried out under different sample thicknesses with the Δd increment of 1 mm and the offset ranging from 1 mm to 6 mm, to obtain the Raman spectral data with different Δd in the both modes. Finally, the experimental spectral results are pre-processed and analyzed to summarize the experimental results.Results and DiscussionsThe spectral data show a negative correlation between feature band Raman intensity and tissue thickness. In the transmission and reflection acquisition modes, the maximum acquisition depths of about 30 mm and 6 mm can be achieved, respectively (Figs. 3 and 4). On this basis, the SORS experiment is performed, and the Raman intensity shows a certain attenuation trend with increasing Δd at 3 mm and 6 mm sample thicknesses in the transmission mode (Fig. 5), which indicates that the photons in this thickness range are less likely to diffuse laterally and more likely to penetrate the sample along a straight line. This trend is especially obvious at 3 mm, and the Raman scattering intensity is more uniform with increasing Δd at sample thicknesses from 9 mm to 30 mm, which discloses that the best results are obtained in the transmission mode with no offset acquisition. In the reflection mode, a layered model with PAT in the surface layer and polytetrafluoroethylene (PTFE) in the deep layer is used for the spectral acquisition, and both signals attenuates with increasing Δd (Fig. 6), but the PTFE signal shows a tendency of enhancing and then weakening relative to the PAT signal with increasing Δd (Fig. 7). The relatively strongest signal of PTFE is obtained from the samples with thicknesses of 3 mm and 6 mm, corresponding to Δd of 4 mm and 5 mm, respectively. This indicates that the SORS under the reflection mode can effectively avoid surface signal interference and acquire deep tissue signals, and the optimal Δd is positively correlated with sample thickness.ConclusionsThe potential of Raman spectroscopy based on a novel fiber optic probe for deep tissue detection is systematically investigated. On this basis, the application of SORS under the transmissive mode indicates that the transmissive mode does not possess the ability to acquire tissue information layer by layer although it has a deeper tissue penetration effect. The reflection mode SORS achieves a deeper acquisition depth (6 mm) than previous studies, validating the Monte Carlo simulation based prediction by Mosca et al., and a quantitative relationship between the detection depth and the optimal Δd is established. It confirms the ability of the SORS under the reflective mode to effectively acquire deep/stratified sample signals. This study not only demonstrates the superior performance of the self-developed fiber optic Raman probe in Raman spectroscopy, but also provides an important experimental basis and a technical reference for the further optimization of the SORS, which is of great significance in promoting the application of Raman spectroscopy in clinical diagnosis.

ObjectiveAlzheimer’s disease (AD) represents the predominant form of dementia, constituting 60%?80% of all dementia cases. The aggregation and oligomerization of β-amyloid (Aβ) in the brain represent hallmark pathological features of AD. While cerebrospinal fluid (CSF) analysis remains the current gold standard requiring a lumbar puncture, plasma-based Aβ detection presents a less invasive and more accessible diagnostic approach. Early plasma-based Aβ detection enables timely intervention and potentially decelerates AD progression, rendering this research significant for clinical and scientific communities. Plasma Aβ level detection is essential for early diagnosis; however, the extremely low mass concentrations of Aβ40 (270?290 pg/mL) and Aβ42 (30?40 pg/mL) present significant detection challenges. Ultrasonic cavitation-based β-amyloid fibril proliferation technology enables protein fibril amplification using trace seeds, and when integrated with fluorescent probe detection technology, facilitates trace β-amyloid detection and fibril aggregation process observation. However, high-power ultrasonic processing and varying incubation periods induce sample temperature fluctuations between 25 ℃ and 40 ℃. Since fluorescent probe excitation and emission spectra demonstrate temperature sensitivity, these variations can affect fluorescence intensity measurements, potentially compromising the accuracy of β-amyloid concentration determination and diagnostic result reliability.MethodsWe selected Thioflavin T (ThT) as the fluorescent detection probe, an established fluorescent probe that selectively binds to Aβ aggregates to form ThT-amyloid fibril complexes. When excited by a 440 nm light source, this complex emits fluorescence at 480 nm, with the fluorescence signal intensity linearly correlating to the Aβ aggregate content in the sample. To address temperature fluctuation effects from high-power ultrasonic processing on fluorescence intensity detection, we examined the temperature sensitivity of excitation efficiency for light sources with varying spectral linewidths, ultimately selecting an optimally linewidth-configured excitation source. Given that ThT’s fluorescence emission spectrum exhibits a red shift with increasing sample temperature, and to eliminate non-fluorescent stray light interference, we investigated fluorescence spectral filtering techniques and examined temperature effects on detected fluorescence intensity using filters of varying bandwidths. To satisfy high fluorescence detection sensitivity and linearity requirements, we implemented single-photon detection technology. Considering the low Aβ sample concentrations and resultant weak fluorescence emissions, we analyzed system stray light sources and developed a combined spectral filtering-based stray light suppression technique to attenuate stray light below the single-photon detector’s equivalent noise power.Results and DiscussionsRegarding the impact of the excitation light source on excitation efficiency, we found that when the spectral linewidth of the excitation light source was 2 nm, the relative change in the excitation spectrum overlap integral decreased by approximately 67% compared to a light source with a commonly used 10 nm linewidth [Fig. 3(b)], indicating that the excitation light absorption efficiency is less sensitive to sample temperature changes. Regarding the effect of using filters with different bandwidths on the temperature sensitivity of detected fluorescence intensity, the study found that when using a fluorescence filter with a bandwidth of 40 nm (passband of 460 nm to 500 nm), the detected fluorescence intensity was least sensitive to sample temperature changes [Fig. 5(b)]. The combined spectral filtering-based stray light suppression technique ultimately controlled the background noise of the detection device to 7 photons (Fig. 17). Experimental measurements on plasma samples with different Aβ concentrations showed that the temperature sensitivity of the detected fluorescence intensity was better than 2.1% [Fig. 18(b)]. Further experiments, by adjusting the output power of the light source to simulate the fluorescence intensity of plasma samples with different Aβ concentrations, demonstrated that within a dynamic range of 957358, the linear fitting coefficient of determination (R2) between the count value and the detected fluorescence intensity reached 0.9996 [Fig. 20(b)].ConclusionsThe developed fluorescence detection device demonstrated robust performance in experimental measurements of plasma samples with varying Aβ concentrations. The measured fluorescence intensity count values exhibited strong linear correlation with Aβ concentration, achieving a linear fitting coefficient of determination of 0.9996. The relative standard deviation across 50 measurements of identical concentration samples remained below 1.3%, indicating excellent measurement stability. Additionally, utilizing a light source with adjustable output power to simulate plasma sample fluorescence intensity at different Aβ concentrations revealed the relationship between count values and fluorescence emission powers. The experimental results demonstrated a linear counting dynamic range of 957358, maintaining a linear fitting coefficient of determination of 0.9996 throughout the entire range. These findings confirm that the developed Aβ concentration fluorescence detection technology achieves high-sensitivity weak fluorescence signal detection, satisfying the requirements for low concentration Aβ detection in plasma samples and advancing early Alzheimer’s disease diagnosis capabilities.

SignificanceParticle sorting plays a crucial role in various fields, including biomedicine and physical chemistry. Traditional sorting techniques, such as those based on acoustics or magnetism, are limited by factors such as low resolution, restricted throughput, and poor selectivity. Optical sorting, which utilizes optical forces or other related optical techniques, has emerged as a powerful alternative. Specifically, optical-force-based sorting exploits differences in the optical forces acting on particles or cells within a light field, which are driven by physical properties such as their shape, size, chirality, or polarizability. Compared to conventional techniques, optical sorting offers significant advantages, including high resolution, non-invasiveness, and broad applicability.The optical tweezers technique, which uses optical forces to manipulate micro- and nano-objects, was pioneered by Arthur Ashkin in the 1970s and 1980s. Since then, optical tweezers have become invaluable tools for capturing and manipulating microscopic particles, opening new avenues of research in biomedicine, physics, and chemistry. In 1997, Steven Chu, Claude Cohen-Tannoudji, and William D. Phillips were awarded the Nobel Prize in Physics for their work on atomic cooling using optical forces. In 2018, Ashkin was awarded half of the Nobel Prize in Physics for his groundbreaking contributions to the development of optical tweezers and their applications in biomedicine.Conventional optical sorting schemes rely on differences in the magnitude and direction of optical radiation and gradient forces acting on particles with various shapes, sizes, chiralities, or polarizabilities. However, these techniques are limited by directional constraints and degrees of freedom, which can compromise the sorting accuracy. In the past decade, two novel optical force mechanisms have been discovered: the optical pulling force (OPF) and optical lateral force (OLF). These forces offer additional degrees of freedom for sorting and have demonstrated significant potential for high-precision and chiral particle sorting. Each of the optical forces (radiation, gradient, pulling, and lateral) displays unique mechanical properties, enabling the manipulation and sorting of nanoscale particles.In addition to optical-force-based sorting, several optically related techniques, such as fiber optic tweezers, fluorescent labeling, and artificial intelligence, provide innovative approaches for sorting particles and cells. Fiber optic tweezers have transformed optical sorting into a cost-effective technology because dual or single optical fibers can be used to efficiently sort small particles or cells. Fluorescent labeling enables precise identification and automated tracking by targeting unique structures within particles or cells. Artificial intelligence facilitates the high-resolution processing and automated analysis of particle images. Current research in optical sorting focuses on developing novel technologies to enhance the efficiency and precision when sorting particles with distinct physical properties.Optical sorting technology plays an important role in many fields, such as material science and biomedical fields. In the biomedical field, it is increasingly used in areas such as genomics, drug discovery and development, proteomics, single-cell analysis, and clinical therapeutics. Optical diagnostics, which is based on the principle of optical sorting, has become one of the most important tools in biomedicine. Its high sensitivity to the physical properties of particles enables the precise detection of small changes in cell morphology and biochemistry, offering promising prospects for clinical applications and therapies.Progress This paper reviews the progress in optical sorting research and discusses the topic in the following orderoptical sorting based on optical forces, sorting using other optical technologies, and the applications of optical sorting technologies across various fields (Fig. 1). The review begins by introducing the theoretical foundations of optical sorting based on optical forces and providing an overview of the research progress in conventional optical forces for sorting applications (Figs. 2 and 3). Next, the mechanisms of novel optical forces such as OPFs and OLFs and their applications in sorting are discussed (Figs. 4 and 5). The review then explores other optical technologies used for sorting, including fiber optic tweezers, fluorescent labeling, and artificial intelligence. Finally, the paper highlights the value of optical sorting technologies in material science and biomedicine, and envisions the emergence of new optical sorting techniques and potential applications in the future.Conclusions and ProspectsOptical sorting technology based on the principle of optical tweezers has significantly advanced the manipulation and sorting of particles and cells, driven by the continuous development of optical tweezers technology.The core principle of optical sorting relies on the differences in the magnitudes and directions of the light forces acting on particles or cells with distinct physical properties. Both conventional and novel optical forces play crucial roles in precisely sorting target particles and cells. Furthermore, the integration of additional optical technologies has broadened the application scope and improved the practical efficiency of optical sorting. For example, fiber optic tweezers provide a high-precision, flexible, and cost-effective sorting method (Fig. 6); fluorescent labeling technology enhances the imaging clarity, photostability, and spectral resolution of particles or cells; and image processing combined with artificial intelligence enables the efficient identification and sorting of particles and cells (Fig. 7).With the ongoing technological advancements and increasing demands across various fields, optical sorting technology is poised to evolve further, driven by emerging innovations. The integration of artificial intelligence algorithms with optical sorting is expected to address current challenges, such as improving the efficiency of high-throughput sample processing and enabling real-time data analysis, thereby facilitating a more efficient and accurate sorting process.Looking ahead, the development of super-resolution microscopy and emergence of new optical materials are anticipated to bring significant breakthroughs to optical sorting technology. Super-resolution microscopy is expected to enhance image resolution, while new optical materials may exhibit unique interactions with different sorting objects. By optimizing these technologies, the applications of optical sorting in biomedicine, materials science, and nanotechnology are likely to expand, paving the way for it to have a more extensive impact in the future (Fig. 8).

ObjectivePhotoacoustic imaging is a non-invasive, functional optical imaging technique that uses the photoacoustic effect with ultrasound as a mediator. Despite its potential for various medical applications, traditional contact-based signal detection methods have hindered its progress in clinical practice. To overcome these limitations, non-contact detection of photoacoustic signals has emerged as a solution. This approach uses air-coupled or all-optical detection methods and achieves a wide bandwidth and high sensitivity for ultrasound signal reception, aligning with the demands of modern medical technology. Current contact-based photoacoustic imaging still faces challenges, such as signal attenuation, surface scattering, system sensitivity, and environmental interference. Therefore, in this study, a noncontact, noninvasive, and cost-effective photoacoustic signal detection device, based on the optical heterodyne technology, is proposed. We aim to address the challenges in photoacoustic signal detection, reduce system costs and complexity, and promote the practical application of non-contact photoacoustic imaging in clinical settings.MethodsThe photoacoustic signals are detected using heterodyne interferometry. First, based on the characteristic parameters of tissue surface vibration signals and the propagation properties of ultrasound waves in a medium, the relationship between the vibration displacement and pressure causing the vibrations is established. Subsequently, by employing the dual-frequency optical heterodyne interferometric theory, the relationship between the photoacoustic signal-induced tissue surface vibration displacement and phase changes is established. Furthermore, I/Q quadrature demodulation is applied to process the photoacoustic signals; this ensures system stability and high demodulation accuracy in complex environments. To achieve all-optical detection of photoacoustic signals, an photoacoustic signal detection system is designed using a He-Ne laser as the detection light source. The optical components are configured to construct an optical-path system for precise detection of photoacoustic signals. In the experiments, an electro-optic Q-switched dual-wavelength Nd∶YAG laser is selected as the excitation light source. This laser allows for flexible control of the excitation light conditions by adjusting the beam diameter and intensity. Finally, the acoustic vibration characteristics induced in the sample under stimulation are evaluated by observing the phase changes and vibration displacement of the photoacoustic signals.Results and DiscussionsIn this study, we investigate the detection of ultrasound vibrations generated by an ultrasound transducer (UST) using a photoacoustic signal full-optical detection system and an immersion probe. A comparative analysis of the measurement results reveals that the heterodyne interference system effectively reconstructs the ultrasound vibrations. The demodulated ultrasound displacement pulse envelope is closely aligned with the measurement result obtained using the immersion probe (Figs.3 and 4). Under constant input parameters, varying the amplitude of the power supply voltage results in a linear increase in the ultrasound signal intensity, which is measured by both the heterodyne system and immersion probe (Fig.5). Furthermore, different driving frequencies are set with constant input signal parameters. The ultrasound vibration frequencies measured by our system and the immersion probe are comparatively analyzed. According to the analysis results, the I/Q quadrature demodulation method accurately extracts ultrasound vibration frequencies with minimal relative measurement error, exhibiting an absolute difference of 0.2 kHz (Table 1). In the absence of excitation pulses, the demodulated baseline interference signal displays subtle displacement deviations with displacement offset control at the nanometer level (Fig.8). The detection of ultrasound vibrations on the surface of a carbon rod demonstrates a close agreement between the ultrasound vibration frequencies demodulated by our system and those measured by the immersion probe (Figs.6 and 7). However, in the case of ultrasound detection on the surface of the porcine liver, the rigidity of measurement mirror M2 leads to higher-frequency vibrations demodulated by our system compared to those measured by the immersion probe (Figs.9 and 10).ConclusionsIn this study, optical heterodyne interferometry and digital Doppler signal demodulation methods are used to experimentally investigate non-contact photoacoustic signal detection. The acoustic vibration characteristics of the target are extracted through the demodulation of the dual-frequency optical heterodyne interference signals. Subsequently, an ultrasonic transducer is employed to simulate the high-frequency vibration signals, and a performance test is conducted. The experimental results demonstrate that the heterodyne system effectively reconstructs photoacoustic vibration signals with minimal relative frequency deviation compared to the immersion probe. In addition, experiments involving a carbon rod and excised biological tissue reveal that the heterodyne system based on the I/Q orthogonal method exhibits superior performance in demodulating photoacoustic signals owing to its insensitivity to changes in the interference signal amplitude. Moreover, the designed photoacoustic signal detection system incorporates linearly polarized light and heterodyne interferometry and the detection sensitivity and precision are enhanced. The heterodyne optical path structure, which is easily adjustable and effective in suppressing interference noise, contributes to the robust performance of the system. By utilizing high-speed data acquisition cards and digital signal processing techniques for interference signal processing, the demodulation algorithm proves to be simple and flexible in design, offering potential cost savings in hardware implementation. The research findings suggest that the proposed system holds a certain reference value for clinical applications in noncontact photoacoustic signal detection.

ObjectiveChina currently has the highest myopia rate among youth in the world, with myopia in children and adolescents becoming the leading cause of visual impairment in the country. Myopia is a progressive condition, but early detection and treatment during the pre-myopia stage can help restore vision. Currently, most children and adolescents rely on traditional computerized optometry in hospitals and ophthalmology institutions for vision screening. However, the monitoring density is insufficient to keep up with the rapid progression of myopia, and if parents notice abnormal vision in their children, they may have missed the optimal intervention period. The objective of this study is to address the issues of bulky and expensive existing computerized optometry and vision-screening instruments. We aim to provide an experimental reference for the miniaturization and instrumentation of refractive measurement systems, enabling their application in scenarios that require portability and miniaturization.MethodsIn this paper, we first provide a detailed introduction to the measurement principles of Shack-Hartmann wavefront sensing technology, followed by the derivation of the wavefront reconstruction algorithm principles. Human eyes with different diopters were modeled using Zemax software, and a Shack-Hartmann wavefront sensor was used to simulate the diffuse reflection phenomenon of a laser spot used as a point light source at the fovea centralis of the human eye, which is located at the center of the retina. The human eye and Shack-Hartmann wavefront sensor were placed at different distances, capturing the outgoing wavefront of the human eye at the corresponding location and imaging it on the detector. This simulated the image acquisition optical path in the refractive measurement system. The collected refractive power images were fed into the algorithm to calculate and then analyze the relationship between the actual measured refractive power and true refractive power at different distances between the human eye and Shack-Hartmann wavefront sensor. Finally, we designed the optical-mechanical structure of an experimental prototype and constructed the system. Model eyes with different diopters were placed at different distances (55, 60, and 65 mm) from the Shack-Hartmann wavefront sensor and measurements were repeated ten times. The actual measurement values were compared with the true values of the model eye to validate the accuracy of the measurements, and the coefficient of variation was used to assess the repeatability of the measurement results.Results and DiscussionsMeasurements on model eyes with different diopters show that the stability of the measurement results is better for myopic eyes than for hyperopic eyes. Additionally, the maximum deviation between the measurement results of myopic eyes and the true values of the model eye is generally smaller than that of hyperopic eyes. This is because the wavefront of hyperopic eyes expands outward after exiting the eyeball, leading to fragmentation of the spot formed on the CMOS sensor by the received wavefront in the Shack-Hartmann wavefront sensor, thereby affecting the centroid-localization accuracy in the diopter calculation algorithm. A certain amount of astigmatism is observed in the measurement results for the diopter of cylinder on model eyes without astigmatism. This is due to the inability to strictly align the main optical axes of the human eye, Shack-Hartmann wavefront sensor, and central area of the CMOS during the device adjustment process, which subsequently affects the calculation of astigmatism values. However, overall, the coefficient of variation for repeated measurements of the diopter of sphere in the diopter measurement results remains below 3%, with a maximum error of 0.2 D. The coefficient of variation for repeated measurements of the diopter of cylinder is below 9%, with a maximum error not exceeding 0.25 D. The measurement accuracy meets the requirements of the “Verification Procedures for Ophthalmic Instruments” (JJG892—2022) of the People’s Republic of China, which stipulates a maximum allowable error for the diopter of sphere within a range of -10 to +10 D with error of ±0.25D, and a maximum allowable error for the diopter of cylinder within a range of 0 to 6 D with error of ±0.25 D.ConclusionsIn this study, we design a compact diopter measurement system based on Shack-Hartmann wavefront sensing technology. The system is calibrated using a model eye provided by the National Institute of Metrology of China to observe the diopter measurement results. An analysis of the results shows that the system’s measurement results are highly consistent with the true values of the model eye, with no significant differences and good repeatability. The system is capable of effectively measuring the diopter within a range of -10‒+10 D, even at non-fixed distances along the z-axis. Furthermore, the system has a simple structure and low cost. It is expected that the size of the device can be further reduced with the future customization of key components, making it more suitable for scenarios requiring miniaturized instruments. Therefore, this system has broad prospects for applications.

SignificanceSurface-enhanced Raman spectroscopy (SERS) is an optical sensing technology based on local surface plasmon resonance, which greatly enhances the Raman signal of molecules adsorbed or very close to the surface of rough nano-metals, even achieving single-molecule detection. The traditional SERS substrate is created by depositing precious metal nanoparticles (Ag, Au, Cu, etc.) on rigid substrates such as slides and silicon wafers. The preparation process of such substrates is relatively mature, offering good stability and sensitivity, and is widely used in molecular recognition, quantitative analysis, and other fields. However, complicated experimental pretreatment steps, high cost, high operational requirements, and fixed detection platform shapes limit the application range of SERS technology, making it unsuitable for sampling and detection of objects with complex shapes and irregular surfaces. To improve the flexibility and portability of detection, reduce costs and operational requirements, and broaden the application range of SERS technology, researchers have focused on developing new SERS substrates, with flexible SERS substrates attracting significant attention. Flexible substrates possess good flexibility and plasticity, and can be cut to any desired shape and size to accommodate various complex shapes and irregular surfaces, offering great advantages in non-destructive and in-situ detection. This review introduces the research progress in SERS technology based on flexible substrates in recent years. Firstly, different methods of constructing flexible SERS substrates using various flexible materials, including cellulose flexible substrates, polymer flexible substrates and other flexible materials, are discussed, highlighting the advantages and challenges of each. Additionally, the latest applications of flexible SERS substrates in biomedicine, food safety, and environmental monitoring are summarized.ProgressFirst, based on the introduction of common materials for constructing flexible SERS substrates, including cellulose, polymer flexible films, and materials from natural organisms, this review outlines different methods for constructing SERS substrates under these materials and discusses their respective advantages and challenges. The natural 3D hotspot structure of cellulose makes it a reliable material for the green synthesis of nanoparticles and the manufacture of flexible SERS substrates. Cellulose paper-based SERS substrates have been widely studied due to their renewability and low cost (Fig. 2), with some unique preparation methods being highlighted (Fig. 3). Polymer films are extensively used in the SERS field due to their flexibility, transparency, and biocompatibility (Fig. 5). Additionally, various biological materials are increasingly attracting researchers’ attention due to their inherent properties or natural structures (Fig. 6). This study also reviews and summarizes recent applications of flexible SERS substrates in biomedicine, food safety, and environmental monitoring methods. Furthermore, the optimization strategies and challenges in various application scenarios based on flexible SERS substrates are summarized and anticipated.Conclusions and ProspectsAlthough flexible SERS substrates have been widely studied, challenges remain in their practical application. Material selection is critical, as uniformity and reproducibility of the SERS spectrum can be affected by varying pore sizes, chemical compositions, uneven distribution of reducing agents, and different aggregation states of plasma nanoparticles at different locations. The preparation process may involve the use of volatile organic solvents that are not environmentally friendly and can release harmful substances, leading to negative environmental effects. Differences between various organisms can impact experimental reproducibility. Adjusting the composition, morphology, and structure of nanoparticles, and introducing surface modification or pretreatment steps can improve substrate performance. Currently, most high-performance SERS substrates rely on precious metal nanostructures, and their high cost hinders mass production. Therefore, it is essential to explore more environmentally friendly, green, and high-performance SERS substrates, including the preparation of renewable substrates and the development of substrates with self-cleaning capabilities. In practical applications, the complex and diverse composition of objects presents a challenge for the multiplexed detection capability of flexible SERS substrates. Thus, combining SERS with other technologies such as molecular imprinted polymers (MIPs), immune recognition, microfluidic technology, and machine learning can help construct a SERS sensing platform suitable for multi-target detection. Furthermore, with the miniaturization of Raman spectrometers, SERS technology is expected to reduce dependence on large Raman spectroscopy instruments. Combined with flexible SERS substrates, SERS technology can potentially offer a new and rapid optical detection method for many special scenarios, including field exploration, emergency incident handling, criminal investigation, entry-exit border inspection, and clinical bedside detection.

ObjectiveIn the microscopic world, laser trapping is an effective method for the precise manipulation of micro-/nano-objects. Conventional optical tweezers are based on the principle of photon momentum exchange, which generates optical forces on the order of piconewtons (~10-12 N). However, overcoming the motion resistance of micro-/nano-objects at solid interfaces is challenging as it typically requires forces on the order of micronewtons (~10-6 N). Owing to their limitations, conventional optical tweezers are typically used in fluid environments, such as vacuum/air and liquids. Trapping and manipulating objects on solid interfaces can be challenging. Scholars have attempted to actuate micro-/nano-objects using pulsed lasers based on the principle of surface elastic waves to manipulate objects in direct adsorption contact with dry solid surfaces (solid-gas interfaces). However, this technique has yet to result in the stable trapping of objects. For techniques that do not offer trapping, a random misalignment between an object’s center of mass and the spot center introduces uncertainty in the direction of motion. This uncertainty hinders the precise, continuous, and arbitrary control of the object’s motion. Photothermal-Shock tweezers enable the laser trapping and manipulation of metallic nanomaterials on dry solid interfaces via the photothermal shock effect. Hence, their application is wide ranging. Additionally, the utilization and maintenance of laser-trapping methods typically necessitate the use of intricate equipment and specialized debugging techniques, which imposes numerous limitations on the operating environment and the personnel operating the equipment. This goal of this study is to design a micro-/nano-object control system based on deep learning. The system will enable the high-precision laser trapping and intelligent motion control of objects at dry solid interfaces via a photothermal-shock tweezer platform.MethodsThis paper presents a micro-/nano-object control system comprising three components: a photothermal-shock tweezer platform, an integrated control module, and an image-feedback module. The composition of the control module and the method of operating the photothermal-shock tweezer platform, including the hardware-structure construction and the corresponding control program design, are analyzed. The resolution and control range of the control module are analyzed via calculation and testing. The image-feedback module of the system is designed to detect the position of micro-/nano-objects in microscopic images and to provide dynamic feedback. The image-feedback module uses the YOLOv8 model for object detection and the OpenCV algorithm for center-of-mass localization. The models mentioned above are trained using a customized dataset created from microscopic images. Subsequently, they are tested on various sample images, and the detection resolution and error are analyzed. Finally, an experimental setup is constructed, as shown in Fig. 1, and motion-control experiments are conducted on multiple samples to evaluate the overall system performance.Results and DiscussionsThe trained YOLOv8 model and OpenCV algorithm are used by the image-feedback module to locate the center of mass in various types of microscopically acquired images (Fig. 5). The average detection error of the module is 116.1 nm. Motion-control experiments are conducted using the overall system. In the experiments, Pd nanosheets measuring approximately 10 μm are used, and a transparent silicon-dioxide sheet is used as the substrate. The system controls the laser to trap the nanosheet sample and actuate it along a predetermined path (Fig. 7). The average control error of the spot is 71.8 nm, whereas that of the sample is 108.9 nm. The data shown in Table 1 indicate that the control system successfully realizes the nanoscale closed-loop control of micro-/nano-objects on dry solid interfaces with a high degree of control freedom and a small control error. Additionally, the sample is tested at varying speeds (Fig. 8), and the system’s control errors at different speeds are obtained experimentally (Table. 2). As the sample’s movement speed increases, the control accuracy of the system decreases. If the sample propagates extremely rapidly owing to the system setting, then it will not satisfy the response time required for the laser spot to re-trap the sample. Consequently, the sample will be outside the trapping range of the laser spot, thus causing the system to lose control of the sample. Within certain limits, the rate at which the sample is re-trapped can be increased by increasing the pulse frequency of the laser (Fig. 9). Thus, the micro-/nano-objects can be guaranteed to remain in the trap at higher laser-spot motion speeds. In addition, the use of higher-quality laser spots, flat-surface substrates, and smaller nanosheets allows objects to be trapped more rapidly and stably. For the control system designed in this study, the samples can be stabilized via numerous experimental trials when the system is specified to propagate at a speed of 5 μm/s or less.ConclusionsA control system for micro-/nano-objects is proposed in this study. Combining this system with image feedback based on deep learning, high-precision laser trapping and the intelligent control of micro-/nano-objects on dry solid interfaces are realized by integrating the control of a photothermal-shock tweezer experimental platform. The system can realize the laser trapping and path control of objects based on the parameter input as well as identify and locate objects in microscopic images via the YOLOv8 and OpenCV algorithms. This method provides dynamic feedback regarding the trapping state of the system, thus enabling the intelligent control of objects. Additionally, the modularized design of the system and the gesture-control method endow the system with a certain level of compatibility and flexibility that facilitates the expansion of functions in different application scenarios as well as the operation and use of personnel in different fields.

ObjectiveThe early and accurate diagnosis of colorectal cancer is difficult to perform owing to its long incubation period and slow development. MicroRNA (miRNA) in exosomes is a non-coding RNA containing 18?22 nucleotides that participate in transcriptional inhibition and post-transcriptional regulation. Thus, it is closely related to the proliferation and migration of tumor cells. Therefore, colorectal cancer can be diagnosed early by detecting the concentration of miRNA in extracellular vesicles.MethodsWe propose a highly sensitive method for detecting miRNA-92a concentrations using terahertz metasurface sensors as detection elements and a mixed-chain reaction (HCR) signal-amplification strategy. In our experiment, we first modified nanogold and a capture probe H0 on a metasurface sensor. Next, we deposited tested miRNAs onto the sensor. Subsequently, we deposited hybrid chains H1 and H2. Finally, we washed uncaptured miRNAs and hybrid chains using PBS buffer.Results and DiscussionsIn this study, a method for detecting the miRNA-92a biomarker in colorectal cancer is devised and verified. This method utilizes the capture probe H0 to bind AuNPs and modify them on a terahertz metasurface sensor. As H0 is designed for miRNA-92a, the modified sensor exhibits good specificity for miRNA-92a. As shown in Figures 7 and 8, the sensor surface is modified using hybrid chains to trigger the HCR reaction, thus forming a DNA long-chain structure and causing a significant shift in the resonant frequency of the sensor.ConclusionsThe experimental results show that the shift in the resonant frequency of the metasurface sensor correlates linearly with the miRNA-92a concentration, and that the maximum detection sensitivity achieved is 6.26 GHz/lgCmiRNA-92a.This method offers the advantages of rapid detection, low detection limit, and high sensitivity, thus rendering it suitable for the rapid detection of cancer-related extracellular vesicle concentrations and the early diagnosis of diseases.

ObjectiveWith advancements in quantum manipulation and optoelectronic detection technologies, the atomic magnetometer, a novel quantum extremely-weak magnetic sensor, has experienced rapid development. Operating in the spin exchange relaxation free (SERF) state, atomic magnetometers offer numerous advantages, including non-cryogenic operation, compact structure, low maintenance costs, and high sensitivity, making them widely applicable in various fields. However, the phenomenon of optical frequency shift, induced by off-resonant circularly polarized pumping light, critically affects the orthogonality of measurement and output response in SERF atomic magnetometers. This study proposes a method for suppressing optical frequency shift based on the analysis of the non-sensitive axis response using a self-made compact single-beam SERF 87Rb atomic magnetometer. The curve of optical frequency shift, combined with the curve of light absorption, is precisely plotted and analyzed to determine the central resonant frequency of the SERF atomic magnetometer. The analysis indicates that employing this suppression method significantly reduces coupling crosstalk between the measurement axes of the magnetometer, thereby enhancing the orthogonality and output response of the sensitive axis. Experimental results validate the effectiveness of this suppression method. Further comparison reveals that the performance of the self-made compact SERF atomic magnetometer is enhanced by suppressing optical frequency shift, resulting in a sensitivity of 13 fT/Hz within a bandwidth of 140 Hz and a dynamic range of approximately ±3 nT.MethodsThe optical frequency shift direction is regarded as the photon spin direction, which is equivalent to the existence of an equivalent virtual magnetic field in the direction of the pumping light (x-axis). Due to this fictitious magnetic field, the sensitive axis (z-axis) of the SERF atomic magnetometer reacts to signals from the non-sensitive axis (y-axis). Applying a weak oscillating magnetic field at 40 Hz to the y-axis and a direct current compensation magnetic field to the x-axis reveals a trend where the response of the y-axis varies with the compensation magnetic field along the x-axis. When the response of the y-axis reaches its minimum value, it indicates completion of compensation for the fictitious magnetic field.Results and DiscussionsAs a result of the suppression method, the response of the 40 Hz signal from the y-axis notably decreases (Fig.2) after compensating for the magnetic field along the x-axis. The variation curve of the compensation magnetic field applied along the x-axis with the laser frequency (Fig.3) indicates that the magnetic field along the x-axis mainly consists of the fictitious magnetic field of optical frequency shift due to the constant residual magnetic field. After analyzing and compensating for the residual magnetic field along the x-axis, approximately 0.2 nT, based on the principle of optical frequency shift, the optical frequency shift curve [Fig.4(a)] is plotted, confirming its existence. Coupled with the light absorption curve [Fig.4(b)], the resonant frequency of 87Rb atoms is determined to be 377109.23 GHz. By optical frequency shift suppression, the measured coupling coefficient is about 4.5%, which can be used to evaluate more accurately the orthogonality between the measured axes and the response of the sensitive axis(Fig.5). With potential coupling crosstalk between the y and z axes accurately eliminated, the response of the z-axis significantly improves after optical frequency shift suppression (Fig.6). As a result of this operation, the self-made compact fiber-coupled SERF atomic magnetometer achieves high sensitivity of 13 fT/Hz within a -3 dB bandwidth of 140 Hz, and its dynamic range is approximately ±3 nT.ConclusionsThis study proposes a method for suppressing optical frequency shift based on analyzing the response of the non-sensitive axis using a self-made single-beam compact SERF Rb atomic magnetometer. By utilizing the proposed suppression method, the phenomenon of optical frequency shift and the existence of its equivalent fictitious magnetic field are verified. The central resonant frequency of the SERF atomic magnetometer is determined from the plotted curves of optical frequency shift and light absorption. Moreover, suppressing optical frequency shift significantly enhances the orthogonality between measurement axes, reduces crosstalk, and improves the response of the sensitive axis of the SERF atomic magnetometer, thus demonstrating the efficacy of the suppression method. The study results indicate that after suppressing optical frequency shift, the bandwidth, sensitivity, dynamic range, and other performance indicators of the self-made SERF atomic magnetometer improve. Its sensitivity can maintain a level of 13 fT/Hz within a bandwidth of 140 Hz, with a dynamic range of approximately ±3 nT.

ObjectiveIntracellular liquid-liquid phase separation is related to various biological processes in cells. Analysis of the phenomenon and the phase separation mechanism can provide a reference and strategy for regulating cell physiological processes and drug development. Phase imaging technology is used in the study of liquid-liquid phase separation because it is highly advantageous for contactless and label-free quantitative observation of colorless transparent objects. However, in this technique, the sample thickness is coupled to its refractive index, and the morphological distribution must be inverted using the corresponding algorithm. The efficiency of the analysis depends largely on the amount of data acquired, time required for calculation and processing, and accuracy. To meet the demand for the real-time acquisition of morphological information of phase-separated condensates in the field of life science research, this study proposes a fast inversion method for three-dimensional morphology using only two phase images and a design of an interferometric phase imaging system with dual optical information acquisition using a single image sensor.MethodsA method for the morphological analysis of liquid-liquid phase separation aggregates is proposed in this paper. The first step in this method is to use a single sensor based on interferometric phase imaging technology to collect two sample phase distribution maps incident in the nonorthogonal directions. The second step is to extract the edges of these phase images. The boundary point coordinates of the agglomerate substructure on the projection surface were detected point-by-point according to the pixel points of each phase image to obtain the structural contours of the sample projection on the two imaging surfaces. The next step is to select and arrange the obtained control points using approximation fitting based on the geometric characteristics of the phase volume. A direct linear transformation was used to select the control points to solve the quantitative relationship between the spatial and projection plane coordinates. Based on this correlation, the corresponding three-dimensional coordinates in the same spatial coordinate system were calculated from the two-dimensional coordinates of the undetermined points. Thus, the three-dimensional shape reconstruction of the phase volume was realized.Results and DiscussionsTo elaborate the principles and steps of the algorithm, this study uses the nucleus model as an example to extract the surface morphology of the liquid-liquid phase separation condensate, such as the internal nucleolus, and establishes a two-medium concentric ellipsoid model (Fig. 2) to simulate the internal structure of the nucleus and design polystyrene microspheres[Fig. 7 (c)]. This reconstruction algorithm yielded better reconstruction results for the two-medium concentric ellipsoid model and polystyrene microspheres [Figs. 6 and 7 (d)]. The reconstruction of the sphere and ellipsoid demonstrated the effectiveness of the algorithm for different feature surfaces and the time efficiency of inversion calculation (Table 2). The processing speed satisfied the requirements of real-time analysis. The rapid reconstruction of the polystyrene microspheres also shows the feasibility of first extracting the relationship between the corresponding projection pixels based on two non-orthogonal phase maps and then quickly inverting the three-dimensional shape of the sample.ConclusionsA method for the morphological analysis of liquid-liquid phase separation condensates was proposed. A single sensor was used to obtain the phase distribution diagrams of the two samples based on interferometric phase imaging technology. The boundary point coordinates of the condensate substructure on the projection plane were detected point-by-point based on the pixel points of the phase diagram, and the structural contours of the sample projection on the two imaging planes were obtained. Based on the geometric characteristics of the phase volume, the control points were selected and arranged using approximation fitting, and a mapping relationship between the three-dimensional space coordinates and the corresponding plane projection coordinates was established. Subsequently, the three-dimensional space coordinates of the phase volume were obtained through plane projection coordinate inversion, and a three-dimensional shape reconstruction of the phase volume was realized. The proposed morphological analysis method only needs to collect two phase diagrams, which requires a calculation time of approximately 0.05 s, which can provide a reference for the real-time detection of transparent objects such as liquid-liquid phase separation. It should be noted that this algorithm is simple and rapid. For the liquid-liquid phase separation of such spherical or spheroid phase bodies, the three-dimensional shape can be efficiently inverted in real time, but the reconstruction of irregular phase bodies still requires improvement in terms of calculation accuracy. The selection of control points to establish two-dimensional-three-dimensional mapping is a key factor. In the future, machine-learning algorithms can be considered to determine their coordinates and numbers. To address the difficulty in selecting control points under experimental conditions, this study proposes an operation scheme for the fitting approximation. The configuration of the appropriate number and location of control points for different feature samples under experimental conditions, according to different detection requirements, is a problem that we are currently exploring.

ObjectiveChlorophyll detection and monitoring play crucial roles in plant physiology, water quality, agricultural management, and ecosystem health. Based on their principles and application characteristics, current chlorophyll detection methods can be classified into several categories such as spectroscopic measurements (such as spectrophotometry and fluorescence techniques), compositional analysis (such as high-performance liquid chromatography, HPLC), and morphological observation (such as microscopic counting and high-resolution spectral imaging). However, many of these methods present various drawbacks. Spectrophotometric methods involve cumbersome detection steps and suffer from low sensitivity; the HPLC method takes a long time and is costly; the fluorescence method does not work well with high-concentration solutions; some detection equipment demands on-site measurement, hindering long-distance detection; and real-time capabilities are often lacking, demanding significant manpower and resources. In recent times, microwave photonics (MWP) technology evolves rapidly. Microwave photonic filters (MPF), pivotal technologies within this realm, capitalize on the fiber optic sensor’s resilience to high pressure, high temperature, corrosion, and electromagnetic interference. These sensors process RF signals and manage optical carrier signal processing within the optical domain. This study introduces a chlorophyll detection system rooted in the microwave photonic filter RF intensity. This novel detection method stands out for its compactness, robust anti-interference capabilities, and potential for long-distance detection. The focus here is the application of microwave photonic filters for chlorophyll detection. Our experiment underscores the feasibility of this principle and highlights a pioneering approach to chlorophyll detection with expansive application prospects.MethodsThe system comprised a broad-spectrum light source (ASE), a microwave signal source (RF), an optical fiber amplifier (EDFA), an electro-optical modulator (EOM), an isolator (ISO), an optical coupler (OC), a photodetector (PD), a spectrometer (ESA), and optical fibers. Together, they formed a microwave photonic filter with a Michelson interferometer structure. The upper arm (reference arm) of the system had a fiber-end-face placed in a test tube containing a matching solution with consistent reflectivity. This matching solution was 95% ethanol, and the fiber end face was labeled as PC1. The lower arm (sensing arm) connected with a 2 km fiber optic, enabling detection and monitoring over extended distances. The end fiber face of this arm was placed in a test tube containing a chlorophyll solution, and its fiber-end-face was labeled as PC2. The principle of chlorophyll determination in this study centered on the variation in RF power at a particular frequency due to shifts in chlorophyll concentration. Following the Fresnel reflection principle, when the chlorophyll content at the optical fiber’s end face varied, the solution’s refractive index (n) altered. This change led to a modification in the effective reflectivity (Fresnel reflection coefficient R), influencing the amplitude coefficients of the microwave photonic filters.Results and DiscussionsChlorophyll solutions extracted from various vegetables are tested (Fig.2) to verify the feasibility of detecting plant chlorophyll (Fig.4). Through the time stability experiment, it is concluded that when the chlorophyll sample solution of the experimental stock solution is placed in a shaded room at a temperature of 25 ℃ for 2 h, the relative error of the maximum value of the RF intensity measured by the chlorophyll solution stays within 0.73%, and the relative error of the minimum value of the RF intensity is within 0.72% (Fig.5, Table 3, and Table 4). This indicates that the chlorophyll solution made by the experimental stock solution remains stable, suggesting the properties of the standard substance do not change notably within the experimental time range, ensuring the reliability of the experiment. Temperature effect experiments show that the system remains more stable concerning the chlorophyll concentration of the experimental samples in the measurement range of 25?35 ℃ (Fig.6). Different gradients of chlorophyll solutions, prepared from chlorophyll experimental stock solution and standard solution, are tested, confirming that the RF intensity and chlorophyll mass concentration maintain a strong linear relationship. For the measurements of the chlorophyll experimental stock solution, the linear degree of fitting (R2) at the maximum RF intensity is 0.9583 with a sensitivity of 0.2994 dB/(mg·L-1), and the R2 at the minimum RF intensity is 0.9596 with a sensitivity of 0.3336 dB/(mg·L-1) (Fig.7). For the measurements of the standard chlorophyll solution, the R2 at the maximum RF intensity is 0.9741 with a sensitivity of 0.007881 dB/(μg·L-1), and the R2 at the minimum RF intensity is 0.9841 with a sensitivity of 0.02258 dB/(μg·L-1) (Fig 8). These experimental results demonstrate that the system exhibits high sensing performance at high and low chlorophyll mass concentrations.ConclusionsIn this study, a novel chlorophyll detection system is demonstrated, which utilizes microwave photonic signals to capture the RF spectral lines of the system. This method extracts chlorophyll sensing information from the peaks (RF intensity maxima and RF intensity minima) without the need for expensive optical spectral demodulation instruments. It offers rapid demodulation speed, enabling real-time long-distance detection and monitoring of solutions with varying chlorophyll mass concentrations. The introduced sensing system exhibits outstanding sensing performance and proves versatile for detection in both low- and high-mass concentration of chlorophyll environments. This research paves the way for future applications in areas such as water pollution monitoring and industrial chlorophyll concentration detection. Beyond detecting the chlorophyll content of various vegetables, this system has the potential for diagnosing plant health and growth, with implications for agricultural development. Although promising chlorophyll mass concentration detection results are achieved, there remains potential for further optimization. This includes reducing noise impact, enhancing system sensitivity and fit, and solidifying its foundation for future applications.

SignificanceWith the development of society, the demand for improved quality of human life is increasing. The threats of cancer, pandemic viruses, declining food safety, and environmental pollution have gradually become the critical issues in human society. Therefore, the early diagnosis and treatment of cancer, development of drugs, rapid and sensitive detection of viruses, monitoring of environmental pollution, and inspection of food safety are vital for human life and health. Early biomarkers of cancer, such as tumor necrosis factor (TNF), exosomes, and circulating tumor DNA, have an extremely low abundance in the human body. Environmental pollution and food inspection have also necessitated the requirements for detecting extremely low concentrations of markers. Therefore, biosensors with high specificity and sensitivity are urgently required to satisfy society’s needs.Many methods have been used to detect various biochemical markers, including polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA), liquid chromatography, and mass spectrometry. The PCR and enzyme-linked immunosorbent assay (ELISA) are the gold standards for nucleic acid and protein detection, respectively. However, the PCR typically requires a long detection time (3?3.5 h), expensive instruments and equipment, specific laboratory environments, and professional laboratory personnel. In ELISA, most antibodies require enzyme labeling, which often results in false positives and affects the parameters, making them unsuitable for early detection. Liquid chromatography-mass spectrometry often requires large and expensive mass spectrometers for operation and has low repeatability. However, sensors based on surface plasmon resonance (SPR) do not require expensive markers, and optical detection methods can prevent physical and chemical contact between the sensors and analytes. SPR biosensors can also perform a simple, cost-effective, accurate, and timely detection of biochemical markers to support rapid medical decisions and actions. Currently, the detection limit displayed by SPR sensors is not inferior to that of PCR and ELISA detection methods; the detection program is simpler and can be automated, which compensates for the shortcomings of traditional detection methods and has significant application potential.With the continuous development of the SPR technology for biomarker detection, researchers have significantly expanded the detection capabilities of SPR sensors. However, traditional SPR sensors are typically susceptible to temperature, have difficulty distinguishing non-specific adsorption, and have difficulty detecting low concentrations and low relative molecular mass analytes. To solve these problems, several research teams have developed methods based on sensor structures and functionalized materials to improve SPR sensor sensitivity. Therefore, a summary of the existing research will guide the future development of this field.ProgressIn this study, we first divide the detection methods of SPR biosensors into five types based on measurements of different parameters by the sensor. We explain the basic principles of various interrogation methods for detecting biomarkers and present a comparison of the advantages and disadvantages of the different interrogation methods (Table 1). In terms of current research progress, the detection methods for SPR sensors are mainly based on two types: angular interrogation and wavelength interrogation SPR biosensors, which have improved detection accuracy and higher convenience. The phase interrogation and Goos-H?nchen shift interrogation types exhibit higher detection sensitivity and accuracy; however, it is still necessary to continue investigating the optimal structure of chips and instruments. For system complexity, the angular interrogation type and Goos-H?nchen shift interrogation type have simpler structures and broader prospects for portable detection. Next, we summarize the research progress in SPR sensor sensitization from the aspects of nanomaterial sensitization and sensor structure optimization, based on the methods recently used by researchers to enhance SPR sensitivity. In terms of nanomaterials, including precious metal nanoparticles, magnetic nanoparticles, and two-dimensional nanomaterials, the enhancement of detection signals is mainly achieved through large-surface loads or localized surface plasmon resonance (LSPR) coupling to enhance the electric field. The optimization of the sensing structure includes the combination of a SPR sensor with a structure, such as a Fabry-Pérot cavity or nanohole array. The Fabry-Pérot cavity reduces the signal loss caused by the metal damping effect by binding the light beams in the nanocavity. The nanopore array achieves a simple and sensitive detection based on significant optical transmission. Finally, we summarize the main shortcomings of current SPR sensors and propose possible solutions.Conclusions and ProspectsOverall, SPR sensors have the advantages of a low detection limit, wide linear range, low sample requirement, high sensitivity, and high selectivity, with high potential for cancer prevention, virus detection, and environmental pollution monitoring. Researchers can apply appropriate interrogation methods to develop portable, highly sensitive, and high-throughput SPR biosensors. By appropriately selecting and combining various sensitization methods, SPR sensors that can overcome existing detection capabilities are developed. Although SPR sensors still face challenges such as high costs and difficulties in achieving portability, SPR sensor technology will advance with the progress in materials and structural science, maintaining excellent characteristics for biomolecular detection while minimizing costs.

SignificanceExtracellular matrix (ECM), which has an important impact on cell morphogenesis, adhesion, proliferation, and differentiation, is a dynamic and complex microenvironment. However, the mechanism by which cells receive and process information through ECM remains unclear. Therefore, investigating the mechanism of interaction between cells and the ECM will be of great significance in cell culture, tissue engineering, and other fields.Research has shown that the microstructure of a material surface can regulate the proliferation, differentiation, and migration of cells. Hydrogels have a certain geometric shape and moisture content similar to soft tissue, and thus can simulate the ECM in vitro as well as locate and deliver therapeutic proteins in a controlled manner as a vehicle for cell transplantation. The patterned surfaces of hydrogels, cell scaffolds, and other microstructures prepared via micro/nano fabrication technology can simulate the growth and development environment of cells in vitro, particularly in a three-dimensional (3D) environment, enabling analysis of the correlation between the shape and function of cells, as well as of the mechanism behind the interaction between cells and the matrix. Traditional methods for preparing hydrogel microstructures have shortcomings including low accuracy and difficulty in regulating the morphology, which limits their application in the future.Two-photon polymerization (TPP) technology, which uses a deep-penetrating near-infrared laser as the light source, is a new micro-nano manufacturing technology with true 3D fabrication capability and high penetration depth. It can be used to fabricate 3D micro-nano structures with arbitrary high resolution and is widely used in micro-nano photonics, micro-electromechanical systems, tissue engineering, and other fields. The 3D hydrogel microstructure prepared using TPP technology has a controllable morphology, high precision, appropriate stiffness, and good biocompatibility. This can better simulate the in vitro microenvironment required in tissue engineering and other fields, demonstrating its great potential for practical applications in the biomedical field. However, most photoinitiators lead to residues in organic solvents, and the generated cytotoxicity has corresponding effects on the biological environment. Therefore, it is necessary to design and prepare biocompatible water-soluble TPP initiators.In summary, the application of hydrogel microstructures prepared using TPP technology in cell culture has made some progress, but there are still a series of challenges in the design of biocompatible TPP photoinitiators as well as in the application of bionics, tissue engineering, and other fields. Therefore, it is essential to summarize the relevant research for a comprehensive understanding of the hurdles in the application of hydrogel microstructures and future development directions.ProgressIn this review, the principle of two-photon polymerization and the research progress on photoinitiators are briefly introduced. Moreover, synthesis methods for water-soluble TPP photoinitiators with high initiation efficiencies have been introduced, including host-guest chemistry, hydrophobic interactions, introduction of non-ionic surfactants, and modification of hydrophilic groups. To enable 3D hydrogel microstructures to be fully applied in the field of biomedicine, TPP photoinitiators must exhibit lower cytotoxicity. Xing et al. efficiently prepared water-soluble TPP photoinitiators with high TPA cross sections and low threshold power through the Witting reaction and host-guest chemical interactions, and fabricated a high-resolution 3D hydrogel microstructure. Gao et al. prepared a new ionic water-soluble carbazole photoinitiator through host-guest interactions (Fig.4) and achieved the low laser threshold of 3.7 mW and high resolution of 180 nm, while the 3D hydrogel microscaffold structure maintained great biocompatibility in an aqueous environment. Introducing a nonionic surfactant or modifying hydrophilic groups is a simple and efficient method for improving water solubility. Li et al. synthesized a series of cyclic benzylketone-based TPP photoinitiators containing sodium carboxylates to enhance the water solubility through an aldol condensation reaction. They were evaluated in the dark using the MG63 cell line and found to have low cytotoxicity. Subsequently, the preparation of a 3D hydrogel microstructure via TPP and its application in biomimetics and biomedicine are introduced. Inspired by the response of the flytrap to external stimuli, Wang et al. used femtosecond laser fabrication technology to obtain intelligent responsive hydrogel microdrivers based on bionic asymmetric structures (Fig.7), achieving and adjusting the grasping and release behavior of microtargets by changing the pH value. Zhang et al. designed and prepared a series of 3D hydrogel microscaffolds with different pore sizes using biocompatible materials, such as PEGDA and PE-3A. The porosity of the scaffold was adjusted from 69.7% to 89.3% by changing the pillars and pillar spacing of the scaffold, and by regulating the cell behavior of the 3D hydrogel microscaffolds with different pore sizes (Fig.12). Finally, problems in the application of 3D hydrogel microstructures and their development prospects are summarized.Conclusions and ProspectsIn recent years, many studies have focused on developing photoinitiators with high initiation efficiencies and low thresholds. To realize photo-crosslinking in an aqueous environment, a series of water-soluble TPP photoinitiators with high initiation efficiencies have been designed and prepared, expanding their applications in biomedical fields such as tissue engineering and drug delivery. Although some progress has been achieved in research on water-soluble TPP photoinitiators, the specific polymerization mechanism in aqueous environments requires further exploration. However, current TPP technology cannot satisfy the requirement for the rapid preparation of a large number of hydrogel microstructures, which hinders the mass culture of cells and tissues in vitro. Therefore, in future, the rapid fabrication of large-area hydrogel microstructures using TPP should be considered.

SignificanceOptical tweezers are a high-resolution force measuring technique invented by A. Ashkin and colleagues in 1986. Optical tweezers, in brief, use a highly focused laser beam that can form a stable three-dimensional trap to manipulate micron-sized particles. Optical tweezers have sub-piconewton force resolution and sub-millisecond time response, which can be widely used in single-molecule biophysics. In single-molecule optical tweezers experiment, traditional optical tweezers geometries include single-trap and dual-trap geometries. Compared with the single-trap geometries, the dual-trap “dumbbell” assay has better stability and noise resistance, resulting in higher resolution and playing an important role in the study of DNA-protein interactions, protein folding and the mechanochemical properties of molecular motors. In this review, we provide an overview on the basic principles of optical tweezers and the experimental setup of the dual-beam optical tweezers in the National Facility for Protein Science in Shanghai. The application and progress of dual-beam optical tweezers in single-molecule biology are summarized, and we focus on investigating some perspectives for future applications.ProgressWhen a photon is absorbed by an absorptive particle, the partial momentum of the photons is transferred to the particle, which in turn generates an optical trapping force that stabilizes the particle. Quantitative calculation of the optical trapping force depends on the wavelength of the trapping light and the size of the trapped particle. When the particle radius is close to or greater than the light wavelength, the optical trapping forces can be calculated from “ray-optics” model. When the particle size is smaller than the wavelength, the electromagnetic scattering theory is often chosen as the calculation model (Fig. 1).Optical tweezers are mainly used in the study of single biomolecules such as proteins and nucleic acids. The systems commonly used in single-molecule optical tweezers experiments include single-trap optical tweezers, dual-trap optical tweezers and angular optical tweezers. These experimental systems involve a variety of geometries, which can be used to directly manipulate single molecules and measure mechanical relevant parameters (Fig. 2). Among them, the “dumbbell” geometry of the tweezers has better stability and noise immunity and higher resolution than other optical tweezers configurations, and these advantages make the tweezers widely applied in single-molecule mechanical properties. The National Facility for Protein Science in Shanghai developed high-precision dual-trap optical tweezers and successfully used them to study the folding dynamics of protein complexes (Fig. 3). In this system, in order to accurately obtain the important parameter of optical trapping force, we chose to use the power spectral density method to calibrate the optical trap stiffness (Fig. 4), and realized base-pair resolution on the measurement of tether extension on the dual-trap optical tweezers (Fig. 5).Optical tweezers provide powerful single-molecule evidence to study the mechanical behavior of nucleic acid and proteins that constitute the major roles in the interpretation of the central dogma in molecular biology (Fig. 6). Stretching dsDNA with dual-trap optical tweezers helps us understand the elastic model of DNA and lays a foundation for exploring protein folding, DNA-protein complex interactions and mechanochemical properties of molecular motors. Dual-trap optical tweezers can reveal the protein folding process at the single-molecule level, detect subtle protein misfolding information, and measure the translation, folding and molecular regulation processes of multi-domain proteins in real time. All those studies offer single-molecule information for understanding and treating neurodegenerative diseases (Fig. 7). DNA-protein binding is closely related to the molecular mechanisms of DNA replication, repair and transcription. The ability of dual-trap optical tweezers to monitor DNA-protein interactions in real time at the single-molecule level has advanced the development of related molecular mechanisms and molecular dynamics (Fig. 8). In addition, dual-trap optical tweezers can be used to study the motion characteristics of molecular motors. Mechanochemical properties of molecular motors are understood by measuring parameters such as step size, velocity, and run length (Fig. 9). Dual-trap optical tweezers can also be used to reveal how molecular chaperones regulate the folding and assembly process of protein complexes to clarify the folding mechanism, and provide the single-molecule basis for physiological processes (Fig. 10).In recent years, dual-trap optical tweezers have been developing continuously. Laser Raman spectroscopy tweezers (LRST) have enabled the simultaneous combination of single-molecule manipulation and Raman spectroscopy measurements without direct contact with the sample. Dual-trap Raman tweezers built on this basis can detect the interaction between cells or stretch a single cell to study the changes caused by deformation (Fig. 11). The combination of optical tweezers and single-molecule fluorescence detection breaks the limitation that optical tweezers can only measure in one-dimensional direction, which enables the study of complex conformational changes at three-dimensional level (Fig. 12). Building on this, the combination of ultra-high resolution imaging technology with dual-trap optical tweezers makes it possible to capture the dynamics of a single protein at high protein concentrations (Fig. 13). Besides, nano-optical tweezers are capable of ultra-precise localization of single nano-objects and can track the changing state of biological macromolecules at high resolution over long periods (Fig. 14).Conclusions and ProspectsAfter more than three decades of development, dual-trap optical tweezers have gradually formed a well-established experimental system in biological research, and the increased temporal and spatial resolution has further extended the application range of dual-trap optical tweezers. At the same time, dual-trap optical tweezers face many challenges in the development and biological application, for example, low throughput or low trap depth and efficiency of living cells. In recent years, although several commercial optical tweezers instruments have been launched for single-molecule studies to promote the single-molecule science, the use of optical tweezers to study single molecules is still developing in China. The National Facility for Protein Science in Shanghai is among the few labs to develop high-precision dual-trap optical tweezers for single-molecule studies. The instrument has high stability and a high signal-to-noise ratio, which has been used in biological single-molecule researches. It is expected that single-molecule experiment using optical tweezers would enter a new phase in China in the coming decade.

SignificanceIn recent years, there has been significant progress in the development and application of nanomaterials in the field of bio-optics. These advancements have led to benefits for medical diagnosis and treatment, such as biosensing, bioimaging, cell tracking, and phototherapy. Nanomaterials possess unique properties that allow for advances in targeting, precision, resolution, real-time and non-invasive detection for bio-optical applications. Among a large number of luminescent nanomaterials, organic semiconducting polymer dots (Pdots) have attracted extensive attention due to their large absorption cross sections, high brightness, stable photostability, excellent biocompatibility, and tunable spectra. Compared to traditional luminescent dyes, which have weak photostability, low brightness, and short lifetime, Pdots have smaller sizes and higher photophysical properties, which contribute to better conversion efficiency and detection results.Pdots have been widely used in the bio-optical field, including in biosensing, bioimaging, and phototherapy applications, which are of great significance for point-of-care testing, in vivo imaging, and tumor therapy. Point-of-care testing based on biosensing technology enables the specific and rapid detection of analytes, which contain significant physiological information. This promotes patient self-management of health. The outstanding sensitivity, response time, selectivity, and reversibility of Pdots make it possible to ensure the convenience and speed of detection while maintaining the same accuracy as laboratory testing. Apart from biosensing, bioimaging technology realizes the visualization of internal structure of organisms and achieves functional imaging for significant medical signals, offering accurate and reliable information for disease diagnosis and treatment. Pdots used as optical probes usually provide near-infrared imaging, which has deeper penetration and lower background interference compared to conventional contrast agents. More importantly, the excellent specificity and tumor targeting capabilities of Pdots enable more effective medical images for in vivo tumor imaging. With their multimodal imaging ability, Pdots have been applied in the field of multimodal imaging, serving as fluorescent probes while giving other imaging signals such as photoacoustic imaging (PAI), magnetic resonance imaging, or computed tomography, which simultaneously provide location and physiological signals of the detection region. In addition, cancer phototherapy depends on energy transfer to damage or kill the tumor cells while avoiding damage to normal tissue, including photothermal therapy (PTT), photodynamic therapy (PDT), and photoimmunotherapy. Traditional therapeutic agents have limited therapeutic efficacy and are prone to cause damage to normal tissue. In contrast, Pdots possess the ability to be easily modified and have high conversion efficiency, resulting in enhanced tumor targeting and smoother drug delivery to the tumor area, which can improve treatment results.The numerous advantages of Pdots make them suitable for bio-optical applications in complex physiological environments, which are highly valuable in biomedical research. Pdots have become one of the crucial materials for biosensing, bioimaging, and optical therapy, aiding in the diagnosis and treatment of diseases, especially in cancer treatment.Progresshe luminescence mechanisms of Pdots are summarized, including fluorescence, phosphorescence, and thermally activated delayed fluorescence (Fig.2). Moreover, this section presents the properties and methods of preparation, modification, and functionalization of Pdots, which are fundamental to their bio-optical applications as specific functional groups enhance the performance of Pdots and extend their range of applications (Fig.3). Firstly, the biosensing applications of Pdots are introduced to demonstrate their potential in the field of point-of-care testing. NADH-sensitive Pdots bound to specific enzymes were used to detect the concentration of metabolites oxidized by NAD+ or reduced by NADH, including phenylalanine (Fig.4), lactate, and glutamate. Similarly, oxygen-sensitive Pdots were coupled with glucose oxidase to achieve blood glucose concentration detection for diabetic self-management (Fig.5). Different modification and functionalization strategies of Pdots enable diverse biosensing applications, including nucleic acids (Fig.6), tumor markers (Fig.7) and enzyme activity (Fig.8). Subsequently, the bioimaging applications of Pdots are presented to show the advantages of Pdots-based probes compared to traditional dyes. Pdots as fluorescence probes ensured in vivo tumor imaging and vascular imaging of mice with a higher signal-to-background ratio and penetration depth (Fig.9). Pdots-based contrast agents have been successfully applied in PAI for brain tumor imaging, thanks to their efficient metabolizable capacity and excellent biocompatibility (Fig.10). Furthermore, Pdots that emitted fluorescent and photoacoustic signals have combined fluorescence imaging with PAI to yield dual-modal imaging. Similar principles were extended to other multimodal imaging (Fig.11). Finally, phototherapy applications demonstrate the capability of Pdots in cancer treatment. Pdots-based PTT agents provided high photothermal conversion efficiency and biosafety to accomplish accurate and effective treatment (Fig.12). The extraordinary energy transfer efficiency and tumor targeting capability of Pdots compensated for the shortcomings of conventional photosensitizers, resulting in inhibited tumor growth in mice (Fig.13). In addition, the use of photoimmunotherapy agents in combination with Pdots enhanced the immune response in the tumor area which suppressed tumor growth and metastasis (Fig.14).Conclusions and ProspectsPdots have been widely used in bio-optical applications such as biosensing, bioimaging, and optical therapeutics. The excellent properties of Pdots allow them to be applied to a wide range of subjects and environments with good results in detection and treatment. In the future, Pdots can be further enhanced in terms of preparation and functionalization, and combined with emerging technologies to achieve intelligent detection and treatment.

ObjectiveBioethanol is an important renewable and clean energy source. Much effort has been put into selecting and constructing ethanol-tolerant yeast strains to improve ethanol yields. However, previous studies have often been limited to screening and obtaining tolerant mutants, with a little in-depth investigation of the phenotypic changes during fermentation. Most studies have been conducted at the population level, which masks intercellular heterogeneity. Microbial cells in a population may exhibit heterogeneity, i.e., individual cells respond differently, under stress conditions. Therefore, developing a phenotypic analysis strategy based on single-cell techniques is imperative for better understanding the stress resistance mechanisms of yeast cells. In this study, Raman tweezers are used to collect single-cell spectra of different yeast strains at different times of ethanol fermentation. Data mining technique using the multivariate curve resolution-alternating least squares (MCR-ALS) method is performed to extract spectra and spectral intensity profiles associated with specific biomolecules and gain insights into the metabolic fermentation processes and adaptation mechanisms of yeast cells.MethodsThree Saccharomyces cerevisiae strains, Bp1, INVSc1, and W303a, are used. After activation in a solid YEPD medium, the yeast strains are transferred to a liquid YEPD medium and incubated overnight at 30 ℃ and 220 r/min. Then, they transfer to a fermentation medium (i.e., 300 g of glucose, 5.0 g of peptone, 0.06 g of CaCl2,0.06 g of MgSO4·7H2O, 1.5 g of KH2PO4,1000 mL of distilled water, and pH 4.5) at 5% inoculum for ethanol fermentation. The optical density at 600 nm (D600) of the culture is measured to estimate the growth of yeast cells. The content of glucose and ethanol in the fermentation broth are determined using Raman spectroscopy.The Raman tweezers are used to acquire the Raman spectra of individual yeast cells. The laser tweezers randomly capture individual cells. The Raman signals of the cells are collected with an acquisition time of 30 s. A self-programmed MATLAB program is used to preprocess the data. The raw spectra are subtracted from the background spectra and then smoothed using the 17-point Savitzky Golay method and baseline corrected using the alternating least squares (ALS) algorithm. MCR-ALS, a chemometric method for resolving the individual, pure components within an unknown mixture, is run using the MATLAB toolbox MCR-ALS GUI 2.0. First, multiple single-cell Raman spectra from different periods are formed into column-increasing matrices. Then, the spectral intensity profiles of the components are initially estimated using evolving factor analysis. To reduce the ambiguity of the resolution results, non-negativity constraints are used for the concentrations and spectra.Results and DiscussionsThe Bp1 strain shows the best fermentation performance, followed by the INVSc1 strain and the worst by the W303a strain. Five or three different biomacromolecules’ spectra and spectral intensity profiles are resolved for each strain, mainly lipid-related substances (phospholipids, triglycerides, and lipoproteins), polysaccharides, or proteins. The content of lipids in W303a strain does not increase significantly during the fermentation. In contrast, INVSc1 and Bp1 strains, which have a higher ethanol production capacity, increase with ethanol volume fraction, showing the prominent role of lipids in the resistance of yeast cells to ethanol toxicity.The Bp1 and INVSc1 strains have high phospholipid content in the late fermentation stage, showing that yeast cells increase ergosterol content to adapt to the accumulating ethanol. It is hypothesized that in strains with high ethanol-producing capacity, yeast cells may increase the synthesis of triacylglycerol, consequently increasing the fluidity of the cell membrane to mitigate the damage by ethanol, thus making the endogenous ethanol flow out more easily. In addition, the cells will also increase the synthesis of ergosterol to maintain the integrity of the cell membrane and therefore have greater stress tolerance and better fermentation performance.The content of major biomacromolecules is relatively homogeneous between cells in the Bp1 strain under the same fermentation conditions (Fig. 3). Simultaneously, cellular heterogeneity is high in the less ethanol-tolerant strains, INVSc1 and W303a (Figs. 4 and 5). This indicates that cell heterogeneity affects the strains’ ethanol fermentation performance and fermentation efficiency.ConclusionsWe apply single-cell Raman spectroscopy combined with MCR-ALS to rapidly obtain information on the variations in the spectral intensity of major biomacromolecules (i.e., phospholipids, proteins, polysaccharides, and triglycerides) in yeast cells during ethanol fermentation at the single-cell level without any a priori information. We find that lipids (i.e., phospholipids, triglycerides, and lipoproteins) and cell heterogeneity have an imperative role in the strain’s fermentation performance and efficiency. Therefore, the method is consistently outstanding in exploring resistance mechanisms in yeast cells and has wide application prospects.

ObjectiveInfectious diseases caused by foodborne pathogenic bacteria are always one of the most severe public health problems. Accurate detection of pathogenic microorganisms in food is necessary to guarantee food safety and to contain bacterial infection. Microbial culture-based methods and biochemical tests are still the golden standard in bacterial detection; however, these methods are time-consuming, taking about 2-3 days to carry out, and follow more than ten operation steps. In addition, new diagnostic technologies, such as conventional polymerase chain reaction, mass spectrometry, and DNA sequencing, suffer from many disadvantages including long processing time, laborious operation steps, limited sensitivity, and high cost; thus, they still cannot meet the requirements for clinical diagnosis and point-of-care testing. In recent years, bacterial detection methods based on surface enhanced Raman scattering (SERS) have achieved significant success and performed excellently on high-sensitivity, easy-to-operate, and fingerprint-based detection methods. In this paper, four major foodborne bacteria, namely, Staphylococcus aureus (S. aureus), Escherichia coli (E. coli), Vibrio parahaemolyticus (V. parahaemolyticus), and Listeria monocytogenes (L. monocytogenes), are used as research objects. Furthermore, a novel SERS method, which combines positively charged Ag nanoparticles (AgNPs+ ) and convolutional neural networks (CNN), is proposed in this paper for accurate and rapid detection of the above four bacteria.MethodsClinical isolates including 10 strains from each of S. aureus, E. coli, V. parahaemolyticus, and L. monocytogenes are collected from the laboratory department of the Affiliated Hospital of Xuzhou Medical University. First, AgNPs+ are prepared via reduction method of NaBH4 and are fabricated in a buffer solution as substrate for SERS. Then, AgNPs@bacteria complexes are formed via electrostatic interactions, and high-quality SERS signals in a shift range of 400-1800 cm-1 of pathogenic bacteria are measured from the forming complexes. Finally, a residual network consisting of 11 one-dimensional convolutional layers (ResNet11) is established and trained on these signals as the spectral classifier. In the spectral identification process, while a SERS spectrum collected from unknown samples is inputted to the trained classifier, the classification probability corresponding to the above four bacteria is calculated, and the label of the maximum value is taken as the predicted label. Based on this strategy, the accurate and precise laboratory testing of bacteria is realized by a high-performance optical analysis technique.Results and DiscussionsIt can be observed from the transmission electron microscope images that AgNPs+ are closely binding onto the cell walls of S. aureus and E. coli in mixed solution. Zeta potential measurement results of AgNPs+ and four bacteria represent the mechanism of the closely combined strong electrostatic attraction between bacteria and AgNPs+ . The spectral measurement results of four types of AgNPs@bacteria complex show that AgNPs+ are an excellent SERS substrate. Mainly in bands of 624 cm-1, 730 cm-1, etc., obvious Raman peaks of the four pathogens with strong intensity are enhanced. By comparing and identifying the functional groups corresponding to the main Raman peaks in SERS fingerprint spectrum, it is confirmed that the SERS measurement results are consistent with the reported literature. In addition, the average relative standard deviation of SERS measurements of ten times is about 7%, which presents well reproducibility. Meanwhile, the differences between SERS spectra from the four bacteria are studied and identified. For these four types of approximate spectra, the trained classifier ResNet11 achieves average accuracies of 99.30% for SERS fingerprints, with bacteria solution molecular concentration of 107 mL-1, and also achieved average accuracies of 98.00% for low-intensity SERS fingerprints with the molecular concentration of 103 mL-1. ResNet11 performs better accuracy and stability compared with other commonly used classification methods, such as Logistic regression, SVM, random forest, and KNN. Furthermore, ResNet11 may promote the practical application level of SERS technology.ConclusionsSERS technology can promise sensitive and label-free detection for bacteria and antibiotic susceptibility testing in single steps. However, achieving practical application remains challenging due to the unstable signal intensity and similar spectral curve. In addition, due to the large size of bacteria (0.5-10 μm), which is far beyond the nano gap that can produce stable SERS hot spots, the SERS enhancement effect of bacteria has always at a lower level. There are two ways to improve the quality of bacterial SERS signal: 1) by improving the stability of the substrate in the experiment; 2) by exploring the excellent combination between the substrate and bacteria. In this paper, AgNPs+ are prepared as SERS sensing substrate. The close and dense combination with bacteria that are negatively charged in solution can provide high-quality signal with high intensity and good reproducibility. On the other hand, novel algorithm of CNN based on residual structure can guarantee the identification accuracy of SERS spectra. It can reduce the opposite impact caused by spectral quality indirectly and can promote the practicability of SERS in bacterial detection. In summary, we propose an accurate and sensitive method for foodborne bacteria detection by using AgNPs+ and CNN. Considering the other advantages including good stability and easy operability, we believe that our approach will become a promising tool for bacterial detection in the laboratory.

ObjectiveThe success of laser hyperthermia techniques depends on precise prediction and control of temperature in the tissue. The study of time-domain analytical solutions can not only verify the results of the numerical models but also contribute to the implementation of technical solutions with few technical errors. Because the excitation time of a laser source is very short compared to tissue equilibrium time, non-Fourier models have become important in theoretical research. Currently, constant heat flux is regarded as a time-dependent physical quantity, which is inconsistent with experiment results in the literatures. In this study, based on modified constant heat flux, a corrected non-Fourier boundary condition is established, and the analytical solution is obtained by integration transformation. The temperature rise and distribution curves obtained using a modified model are consistent with the experimental results in the literatures. In addition, the time-independent non-Fourier boundary condition is inconsistent with the thermal equilibrium. Furthermore, the different heat transfer mechanisms of the single-phase lag model (SPLM) and double-phase lag model (DPLM) under modified non-Fourier boundary conditions are analyzed, and their differences from those of existing models are discussed. The result shows that the time factor should be considered in constant-heat-flux models of biological tissues, otherwise the predicted results will be inconsistent with the experiment results.MethodsBased on the delayed non-Fourier law, which includes non-Fourier single- and two-phase lag equations, non-Fourier heat conduction equations of biological tissue in one-dimensional space were established, including an SPLM, a DPLM, and the classical Peens biological model (PBM). Considering the strong scattering biological surface, the time-dependent non-Fourier boundary condition of constant-heat-flux irradiation was established, and the theoretical solution was obtained via integration transformation under a quasi-static initial condition. Also, a theoretical solution of the time-independent constant-heat-flux irradiation problem was obtained.Results and DiscussionsBased on the obtained analytical solutions, the heat transfer mechanism among PBM, SPLM, and DPLM are discussed and compared to some results in the literatures. The obtained results are as follows:1) When constant-heat-flux is treated as time-independent, the temperature distribution at any time does not obey the law of energy conservation, and among PBM, SPLM, and DPLM, the temperature distribution predicted by PBM is the highest at any time, whereas that of SPLM is the lowest. Also, the temperature variation of SPLM has no jump in wavefront at any position [Fig. 2(a)].2) The temperature distribution of a closed solution with a corrected boundary condition at any time obeys the law of energy conservation, and among PBM, SPLM, and DPLM, the temperature distribution predicted by SPLM at any time is the highest, whereas that of PBM is the lowest, and that of DPLM prediction is between them near the surface. It is worth noticing that only SPLM predicts a sudden rise in wavefront, while DPLM and PBM do not. [Fig. 2(b)].3) Under the corrected non-Fourier boundary condition, SPLM predicts a rapid jump in the temperature change at all positions, which is consistent with the experimental results in the literatures (Fig. 3). Under the wrong non-Fourier boundary condition of time-independent heat flux, PBM predicts a faster change in temperature than SPLM and DPLM, whereas the temperature is the highest, which is in contrast to the experimental results in the literatures.4) Space-time temperature fields were compared. The corrected wavefront of SPLM is like a vertical cliff [Fig. 5(a)], which differs from the existing wavefront [Fig. 7(b)]. Besides, due to the wrong boundary conditions, the corresponding temperature predicted by PBM (Fig. 4) is higher than that of DPLM and SPLM (Fig. 7).5) Under the corrected non-Fourier boundary condition, the bigger the heat-flux lagging time τq,the lower the thermal velocity, and the higher the rising amplitude when the lagging time of the temperature gradient is fixed (Figs. 8 and 9). At a constant lagging time of heat flux τq,with an increase in the temperature gradient time τT,the temperature predicted by DPLM decreases at all positions (Fig. 11), and the lower temperature at any time less than that of the SPLM near the surface (Fig. 10). These results are consistent with the experimental results in the literatures, but the existing constant-heat-flux boundary conditions are very different, and many conclusions are opposite.ConclusionsBased on the results, we conclude that:1) When constant-heat-flux is regarded as time-independent, the temperature distribution at any time is inconsistent with the law of energy conservation. Thus, time-independent boundary conditions cannot satisfy the heat balance equation on the boundary.2) With a corrected boundary condition, the temperature distribution at any time obeys the law of energy conservation. Thus, the corrected boundary condition is energy conservation and satisfies the non-Fourier biological heat transfer equation.

ObjectiveDiabetes mellitus is a chronic and noncommunicable disease with complications in the retina, heart, kidney, and neural system. The effective monitoring of blood glucose level is crucial in the prevention, diagnosis, and management of diabetes. Compared with single-point detection, a continuous glucose monitoring system can track the blood glucose fluctuation and help in predicting the trend of blood glucose change. Recently, various continuous glucose monitoring systems have been developed. The most widely used monitoring modality is electrochemical sensors, which collect glucose information in the interstitial fluid using an implanted enzyme-immobilized electrode. However, electrochemical sensors have some issues, including the limited glucose monitoring time and the risk of infection. Conversely, transdermal detection-based optical sensors exhibit prolonged service time and decreased risk of infection. Luminescent nanoparticles have shown great potential in biological applications because of their high brightness, high photostability, and good biocompatibility. Here, we developed a continuous glucose monitoring system based on a visible-light-excited nanoparticle transducer. We experimentally demonstrated that the nanoparticle transducer is promising for sensitive glucose detection. The visible-light-excited transducer shows potential in long-term and high-frequency monitoring in practical applications with reduced side effects compared with ultraviolet radiation.MethodsThe nanoparticles were prepared using a visible-light-excited fluorescent molecule and the oxygen-sensitive phosphorescent dye via the reprecipitation method. The resulting nanoparticles were characterized via UV-Vis absorption spectra, transition electron microscopy (TEM), and dynamic light scattering (DLS) measurements. The glucose-sensitive nanoparticle transducer was formed by modifying glucose oxidase onto the surface of nanoparticles via EDC-catalyzed bioconjugation. The successful bioconjugation of oxygen-consuming enzyme onto the nanoparticle was characterized by the change in hydrodynamic diameters and zeta-potentials. The biocompatibility of the nanoparticles was characterized through cytotoxicity experiment. The glucose sensitivity of the nanoparticle transducer was examined by measuring the emission spectra under different glucose concentrations (0-20 mmol/L). The intracellular glucose sensing of the nanoparticle transducer was performed on MCF-7 cells. The MCF-7 cells were incubated with the nanoparticle transducer first in a sugar-free medium. Additional glucose solution was introduced with the final concentrations at 20 mmol/L. The luminescence images under different glucose concentrations (0 and 20 mmol/L) were captured.We investigated the in vivo glucose monitoring performance of the nanoparticle transducer. The nanoparticle-GOx transducer (50 μg/mL) was subcutaneously implanted in the lower back of mice under anesthesia. The blood glucose concentrations of the mice were elevated by the intraperitoneal injection of glucose solutions (1 mol/L, in Milli-Q water). Subsequently, blood samples were collected from the tail of mice, and the blood glucose concentrations were tested using a commercial glucometer. Using a small animal biophotonic imaging system, the luminescence images of the subcutaneously implanted nanoparticle-GOx transducer were collected. The luminescence intensity of the implanted nanoparticle transducer was measured and compared with blood glucose concentrations. The mice with the intraperitoneal injection of PBS were adopted as the control group.Results and DiscussionsThe oxygen-sensitive nanoparticle comprises a fluorescent molecule DPBF, an oxygen-sensitive phosphorescent dye PdTFPP, and a functional polymer PSMA. The resulting nanoparticles have a hydrodynamic diameter of 18 nm, as indicated by the TEM and DLS results. The successful bioconjugation of glucose oxidase onto the nanoparticle surface was characterized by the increased hydrodynamic diameters and zeta-potentials. According to the spectroscopic experiments, the phosphorescence intensity (~672 nm) of the nanoparticle-GOx transducer increased as the glucose concentration increased, whereas the fluorescence intensity (~490 nm) remained unchanged. The designed ratiometric sensing system can help in eliminating the luminescence fluctuations caused by the variation in excitation intensity and environmental conditions. The nanoparticle-GOx transducers exhibited a fast response time to distinguish different glucose concentrations. The luminescence spectra of the nanoparticle-GOx transducers under different glucose concentrations were measured within 10 min after adding glucose to the solution. A good correlation was exhibited between the luminescence intensity of the nanoparticle-GOx transducers and glucose concentrations.The cell viability of the MCF-7 cells did not change considerably after incubating with the nanoparticles at different concentrations. The results indicated that the nanoparticles are biocompatible for the following intracellular glucose sensing experiments and in vivo glucose monitoring experiments. The nanoparticle-GOx transducer exhibited a reversible response to glucose, and the monitoring performance remained unchanged for more than 10 repetitive tests. The nanoparticle-GOx transducer exhibited excellent photostability against hydrogen peroxide and free radicals. The reversible response and excellent photostability enabled the stable and long-term continuous glucose monitoring. After adding glucose, the luminescence intensity of the internalized nanoparticle transducers by the cells was obviously enhanced, indicating that the nanoparticle transducer has the potential for intracellular glucose sensing. For in vivo glucose monitoring, we collected the luminescence images of subcutaneously implanted nanoparticle transducers. The transdermal detection of the nanoparticle transducers was achieved because of its high brightness. After the intraperitoneal injection of glucose solution, the luminescence intensity of the subcutaneously implanted transducers increased with the increased blood glucose concentrations, whereas in the control group, the luminescence intensity and blood glucose concentrations remain unchanged after the intraperitoneal injection of PBS. These results indicate that the luminescent nanoparticle transducers are promising for in vivo continuous glucose sensing.ConclusionsWe developed a continuous glucose monitoring system based on a visible-light-excited luminescent nanoparticle transducer. The nanoparticle transducer can be used for the transdermal detection of blood glucose because of its high luminescence brightness. We demonstrated in vitro cellular glucose sensing and in vivo glucose monitoring in animal models. With the ratiometric sensing system, the signal fluctuations caused by the variation in excitation intensity and environmental conditions would be eliminated. The visible-light-excited transducer can also avoid the side effects induced by ultraviolet radiation, indicating the potential for long-term and high-frequency monitoring in practical applications.

ObjectiveClustered regularly interspaced short palindromic repeats (CRISPR) has shown significant promise as an emerging nucleic acid detection technology. However, it still requires improvement in terms of sensitivity, detection automation, and anti-pollution. Furthermore, CRISPR technology lacks simple and portable professional equipment to meet the high demand of rapid point-of-care testing. Therefore, this study proposes a CRISPR/Cas12a detection reaction system for SARS-CoV-2. This detection response system and innovative tube-in-tube consumables aid in developing a portable compact device for simultaneous automatic detection of several samples and a coaxial fiber-based fluorescence detection system. Finally, we developed a single-sample user-friendly nucleic acid detection APP based on smartphone recognition and detection results for the manual detection mode.MethodsThe target in this study was severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), which was detected using the CRISPR method and enhanced via the reverse transcription-recombinase polymerase amplification (RT-RPA) technique; the feasibility was assessed using the reverse transcription-polymerase chain reaction (RT-PCR) amplification method in the early stages. Various companies customized the required reagents and the designed sequences. In the detection process, first, with the tube-in-tube consumables developed by our team in the early stage, which comprised the reaction outer and inner tubes, the amplification reagents and detection reagents were loaded into the inner and outer tubes, respectively. The temperature was regulated to 37-42 ℃ to complete the amplification. The reagents in the inner and outer tubes were then mixed by shaking or centrifugation, and the temperature was adjusted to complete the CRISPR reaction. Finally, it was possible to observe if there was any fluorescence occurrence under the illumination of a blue light. The detection instrument was composed of an optical cassette and a base, and automatic detection was realized through a printed circuit board (PCB), a human-computer interaction display screen, etc. In addition, this study also used the fluorescence image recognition algorithm to process the detection images, compared with the international standard polymerase chain reaction (PCR) technology to explore the detection limit, and increased the target types to test the specificity strength.Results and DiscussionsThe lower part of the detection instrument designed by our team integrates the printed circuit board and the human-computer interaction display screen. In the automatic detection mode, the fluorescence recognition circuit was designed with the help of a 470 nm light-emitting diode (LED), an optical filter, a complementary metal oxide semiconductor (CMOS) camera, a collimating lens, and a coaxial fiber. At the same time, the specificity of the theoretical experiment was verified through comparative experiments on several different targets. In addition, to verify the accuracy of this method for detecting actual samples, we compared each actual sample through PCR detection and the method based on the combination of RT-RPA and CRISPR proposed in this study. The detection results showed that the two were perfectly consistent.ConclusionsThe current study proposed a CRISPR/Cas12a-based anti-pollution portable nucleic acid detection technique. Furthermore, a simple model was proposed based on the naked eye or smartphone to recognize results; additionally, a downsized portable device based on fluorescence detection that can simultaneously detect numerous samples was constructed. The portable device can detect numerous samples simultaneously, and it has a constant heating mechanism and fluorescence stimulation detection optical channel to enhance the detection system’s accuracy and stability. The nucleic acid of SARS-CoV-2 was verified using the proposed method and detection system. The minimum detection limit was

SignificanceIn 2009, influenza A (H1N1) broke out in Mexico and the United States, influencing 214 countries and killing at least 14000 people. The novel coronavirus epidemic which broke out in 2020 has still been raging all over the world for two years as the results of the huge difficulty in the rapid and real-time epidemic prevention detection and the other reasons. In addition, the spread of other viruses including dengue virus (DENV) and human immunodeficiency virus (HIV) is also threatening human health significantly. Virus detection is the key to curb the spread of the viruses.At present, enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR), as the gold standard in the field of virus detection, can be used to detect and trace virus samples with a high sensitivity. But these samples need to be collected to the laboratory, and the viruses must be isolated and determined using the sophisticated lab equipment operated by professionals in order to get accurate results. Surface plasmon resonance (SPR )and local surface plasmon resonance (LSPR) biosensors may be an effective alternative, as their structures are simple and easy to be miniaturized. Especially, the LSPR-based device only needs a light source and some sensing elements. Once the sensing elements successfully capture the virus, the detection process will be quickly, sensitively, and selectively finished. These characteristics of the SPR and LSPR techniques show their great application potential in the field of virus detection, especially for the point-of-care testing with limited conditions.With the rapid development of SPR and LSPR-based virus detection researches, researchers have reviewed the progress of materials and structures of sensors, methods for plasmonic virus detection, and their characteristics of signal amplification, and so on. According to the four general virus detection methods and starting from the four kinds of target analytes captured by the sensor, this paper systematically outlines the latest researches of the SPR and LSPR techniques for detecting viruses, which are of great significance for their clinical application (Fig. 1).ProgressFirst, according to the four methods for virus detection, the application progress of SPR and LSPR in the fields of antibody, antigen, nucleic acid, and virus particle detection is reviewed successively. For the SPR or LSPR sensors based on the binding principle of specific antigen-antibodies, the detection limit is further optimized by modifying the appropriate antigens or antibodies. More stable and inexpensive aptamers and molecularly imprinted polymers are expected to replace antibodies as sensor recognition elements to detect virus antigens or particles. Because the number of virus genomes in clinical samples is usually very small, the detection of nucleic acid by SPR or LSPR alone is limited. However, the detection of virus samples with the concentration at the femto scale can be realized by combining SPR or LSPR with DNA amplification and fluorescent substances. Second, the problems of biological medium contamination and repeatability encountered by biosensors as well as their solutions are introduced (Fig. 13). As for the contamination of biological media, self-assembled monolayers (SAM) can be synthesized on the surface of sensor elements to alleviate this problem. Riedel et al. further reduced or even completely inhibited the biological contamination of plasma and serum by synthesizing polymer brushes. In order to ensure the repeatability of sensing elements, Yoo et al. used magnetic beads replaced under the control of magnetic field as the sensing element, allowing that the sensor chip could still work stably after many repeated measurements. Third, the configurations and parameters of the SPR and LSPR sensors for virus detection in the past 15 years are listed (Table 1), and the advantages of the SPR and LSPR techniques are described. Finally, the optimization strategies of the SPR and LSPR techniques and the present existing problems are summarized. Moreover, the application prospect is also forecasted.Conclusion and ProspectAccording to the current research progress, the optimization strategy of the SPR sensor mainly focuses on film material sensitization and metal particle coupling sensitization. The former includes the application of 2D materials and molecular imprinting through the construction of surface films to enhance practicality and applicability. In contrast, the latter uses nanoparticles to form sandwich structures. The LSPR sensing strategies are concentrated on the design and optimization of nanoparticles or nanostructures, which are often combined with fluorescent substances such as quantum dots (QDs) to form sensing probes for virus detection by the light absorption peak shift or the fluorescence intensity change. The LSPR biosensors are normally easier to be miniaturized than the SPR counterparts. In a word, the SPR and LSPR sensors show great application prospects in the field of virus detection. Predictably, owing to the diversity of the SPR and LSPR virus sensor modifiers, it may be possible to detect specific viruses for multiple target analytes at the same time through the integration of sensor recognition elements, which enables the multi-dimensional evaluation of virus infection in a short time to avoid false negative and false positive cases.