Fig. 1. Schematic diagram of two types of trapping effects of optical-thermal tweezers. (a) Photothermal heating capture^[24];

Fig. 2. Schematic diagrams of thermodynamic effects in photothermal tweezers^[24]. (a) Thermophoresis; (b) thermoelectricity; (c) heat-mediated diffusiophoresis; (d) natural convection; (e) Marangoni convection

Fig. 3. Working principle of OTENT and schematic diagrams of opto-thermoelectric capture of single particle on single gold nano-antenna structure^[31,65]. (a) Modification using surfactant CTAB; (b) formation of positively charged CTAC micelles; (c) schematic diagram of negatively charged chloride ions; (d) in the absence of optical heating, individual metal particles and multiple ions dispersed in solution; (e) thermophoretic migration of individual metal particles and multiple ions under optical heating; (f) action of thermal forces generated by photothermal heating on particles; (g) simulation results of in-plane temperature gradients and corresponding capture force directions; (h) simulation results of out-of-plane temperature gradients and corresponding capture force directions; (i) when laser is off, dispersion of positively charged nanoparticles and multiple ions in solvent around gold nano-antenna; (j) when laser is illuminated, nano-antenna captures nanoparticle at center of nano-antenna; (k) three-dimensional view of opto-thermoelectric capture of nanoparticles on gold nano-antenna; (l) dark-field optical images of 100 nm and 200 nm gold particles and 100 nm and 200 nm silver particles captured at center of tnano-antenna array

Fig. 4. Working principle of graphene-based opto-thermoelectric tweezers (OTET)^[36]. (a) Schematic diagram of OTET with graphene as the substrate; (b) continuous images of PS particle being stably captured and dragged to left by laser; (c) schematic diagram of patterned graphene OTET; (d) experimental setup of capture system; (e) direct laser writing to print S and Z-shaped graphene dot arrays; (f) corresponding experimental results of capturing multiple PS particles; (g) schematic diagram of dynamic manipulation of multiple particles on graphene dot array; (h) experimental results of dynamic movement of partic le arrays

Fig. 5. Working principle of HAONT^[60]. (a) Microfluidic channel; (b) capture of PS particles in dilute PEG solution; (c) capture of gold nanospheres (AuNS) in semi-dilute PEG solution; (d) statistical chart of capture of PS and AuNS particles of different sizes at different PEG volume fractions; (e) material model of AuNS existing in PEG networks with different correlation lengths

Fig. 6. Working principle of ORT^[32]. (a) Schematic diagram of local laser cooling and thermophoretic capture of cold spot particles on Yb∶YLF crystal substrate; (b) in-plane temperature distribution at solution-substrate interface under laser intensity of 25.8 mW·μm^-2; (c) out-of-plane temperature distribution simulated based on temperature curve through center of laser beam in Fig. (b); (d) distribution of in-plane temperature gradients corresponding to Fig. (b); (e) average temperature profile along center of laser beam and peripheral temperature gradient values corresponding to Fig. (d); (f) effective thermophoretic capture force and potential along dashed line in Fig. (d)

Fig. 7. Working principle of HOTTs^[23]. (a) Under normal ambient temperatures, thermophoretic force (F_th) typically repels particles away from laser; (b) in HOTTs, F_th becomes attractive force at lower ambient temperatures; (c) schematic diagram and time-lapse optical images of particle capture in HOTTs; (d) at low ambient temperature of 4 ℃, same particles are captured by laser beam

Fig. 8. Working principle of OTER based on light-driven micro/nano rotors^[80]. (a) Experimental setup and operational schematic diagram of OTER for micro/nano particles; (b) working principle of OTER

Fig. 9. Working principle of OPN and capture and manipulation using pulsed laser-induced photothermal tweezers ^[83]. (a) Schematic diagram of OPN on solid substrate; (b) in the absence of heating, 200 nm gold nanoparticles are bonded with CTAC layer; (c) under laser heating, surrounding CTAC layer releases its bonding with gold nanoparticles; (d) simulated temperature distribution around 200 nm gold nanoparticle; (e) gold nanoparticles move against position of laser beam under influence of in-plane optical forces and drag forces; (f) continuous dark-field optical images of 300 nm gold nanoparticle being manipulated in real time; (g) tilted nanowire rotating on substrate under action of photothermal tweezers; (h) continuous superimposed motion trajectory of 3.7 μm nanowire moving away from center of light spot and rotating, confirming capture behavior; (i)-(l) schematic diagrams of motion trajectories under action of photothermal tweezers

Fig. 10. Photothermal electrocapture and printing of colloidal particles. (a)‒(d) Capture and printing of individual 2 μm polystyrene (PS) sphere particles using single laser beam^[34]; (e) bright-field optical image of “TMI” pattern printed on substrate with 1 μm PS sphere particles^[34]; (f) dark-field optical image of 3×3 array of 500 nm PS sphere particles printed on substrate after drying^[34]; (g) basic principle of bubble pen lithography technique^[88]; (h) schematic diagram of photothermal programmable liquids^[89]

Fig. 11. Based on metal surface PTT^[14]. (a) Immersion SERS imaging technology based on PTT; (b) PTT experimental setup for super-resolution dynamic SERS imaging; (c) bright-field imaging of the MoS2 flake; (d) Raman imaging of MoS2 flake based on PTT system; (e) histogram of edge scanning result; (f) modulation transfer function (MTF) result of edge scanning image

Fig. 12. Intracellular SERS detection based on graphene photothermal tweezers^[37]. (a) Schematic diagram of in-situ intracellular Raman spectroscopy detection process assisted by photothermal tweezers; (b) experimental setup used for graphene photothermal optical tweezers system; (c) microfluidic channel on graphene substrate; (d)(e) positions of Ag nanoparticles in yeast cell; spectral curves detected by individual silver nanoparticles located (f) close to yeast membrane and (g) away from yeast membrane

Fig. 13. Working principle of CRONT^[61]. (a) Schematic diagram of three components in solution; (b) optical system setup; (c) distribution of three components in solution without optical heating; (d) photothermal force-induced particle migration and conjugation dissociation of DNA@AuNS upon optical heating; (e) observation of dissociation effect after ceasing optical heating