Fig. 1. Comparison between SPP and LSP modes. (a) Schematic diagram of propagation SPP; (b) schematic diagram of LSP

Fig. 2. Plasmon decay mechanisms and related processes. (a) Plasmon decay pathway^[2]; (b) rate of carrier production by SPR decay in gold nanoparticles^[4]; (c) photoexcitation and decay processes in SPRs^[3]

Fig. 3. Advances in the applications of plasmonics in biomedical field

Fig. 4. Evanescent field properties and dispersion relation of SPP^[9]. (a) Penetration depth of evanescent field in the direction normal to the interface on both sides of the interface; (b) dispersion relation curves of SPP

Fig. 5. Refractive index sensing and its application. (a) Classification of SPR sensors; (b) schematic of MetaSPR sensor based on gold-platinum nanoflowers for the detection of SARS-CoV-2 neutralizing antibody^[18]; (c) schematic of miRNA-141 detection based on GO-AuNPs^[21]; (d) schematic of grating SPR sensor combined with microfluidic technology for the detection of Alzheimer's disease markers^[27]

Fig. 6. Synthesis and schematic working principle of ultra-bright fluorescent labels based on gold nanorods^[31]

Fig. 7. Conventional Raman enhancement and its application. (a) Multiplex acute myocardial infarction biomarker detection based on SERS-LFA^[54]; (b) multiplex inflammatory biomarker detection based on SERS-VFA^[55]; (c) active microfluidic chip-based SERS detection of multiplex extracellular vesicle protein of melanoma cells^[56]; (d) passive microfluidic chip-based detection of multiplex extracellular vesicle protein of lung cancer cells^[57]; (e) schematic diagram of spectral analysis of urine in combination with handheld Raman spectrometer^[58]

Fig. 8. High-performance plasmon-enhanced SERS substrate. (a) Schematic of Au-truncated octahedral double-edge nanoframework^[62]; (b) tetrameric nanocluster assembly process, where AuNPs and dyes can be immobilized site-specifically on rhombic super-crepe origami by DNA hybridization^[63]; (c) DNA origami scaffolding of nanorods for tip-to-tip assembly process^[65]; (d) pattern-recognition-induced assembly process of gold nanocubes^[66]; (e) preparation process of nanofilms of di-perfluorophenyl-substituted tetrathiophene structures^[68]; (f) demonstration of ultrathin two-dimensional metal-organic skeleton nanosheet structures^[69]

Fig. 9. Frontier research on digital SERS. (a) Three-dimensional nanostacked plasma crystal array for digital SERS substrate^[71]; (b) graphene‒periodic Au pyramidal nanostructures for digital SERS substrate^[72]; (c) gold nano-pocket integrated paper filtration device for digital SERS detection^[73]; (d) colloidal digital SERS detection^[74]; (e) gold-topped nanobead array combined with SERS nanotagas for digital SERS detection of inflammatory factors^[75]; (f) digital SERS based on core‒shell SERS nanotags for IL-6 detection^[77]

Fig. 10. Spaser and its application. (a) Comparison of Spaser and conventional laser; (b) live cell imaging with a single-particle Spaser based on a gold-core silica-shell^[81]; (c) plasmonic laser particles and cell labeling^[82]

Fig. 11. Applications of direct plasmonic photothermal sensing. (a) Schematic diagram of LFA based on photothermal colorimetric detection^[87]; (b) heating performance of various isoexcited photothermal nanoparticles^[88]

Fig. 12. Applications of indirect plasmonic photothermal sensing. (a) LFA based on photoacoustic signal detection^[89]; (b) ELISA based on photoacoustic signal detection^[90]

Fig. 13. Plasmonic photothermal PCR. (a) Ultrafast photothermal PCR based on gold nanofilm with LED excitation^[94]; (b) plamonic heating-based digital PCR workflow^[95]

Fig. 14. Plasmonic tweezer for bioparticle manipulation. (a) Plasmonic tweezer based on a bowtie nano-aperture capturing polystyrene nanoparticles and the successive motion of the tip^[121]; (b) working principle of plasmonic tweezer based on Au NPs‒ZnO nanorod hybrid structure^[123]; (c) lipid vesicle manipulation with thermophoreis derived from plasmonic heating^[124]

Fig. 15. Plasmonic tweezer for biomolecule manipulation. (a) Schematic of optical plasma tweezers-coupled SERS platform and experimental and theoretical values of SERS signals for Tyr at different pH^[126]; (b) DNA plasma manipulation using a combination of optical and thermoselectrophoretic forces—separation of different sized DNAs from a mixed solution^[127]