Fig. 1. Structure diagram of prism coupled SPR sensor^[12]

Fig. 2. Couple types of SPR sensor^[7]. (a) Kretschmann prism coupling; (b) optical fiber coupling; (c) grating coupling

Fig. 3. Intensity interrogation SPR sensors. (a) Schematic diagram of the detection principle of the intensity interrogation SPR sensor; (b) schematic diagram of the dual wavelength SPR imaging system^[17] (L1‒L5: lens; DA: diaphragm aperture; MF: multimode fiber; DM: dichroic mirror; P1 and P2: polarizer)

Fig. 4. Angular interrogation SPR sensors. (a) Schematic diagram of the detection principle of the angular interrogation SPR sensor; (b) angular interrogation SPR sensor for detecting nitrogen content^[23]

Fig. 5. Wavelength interrogation SPR sensors. (a) Schematic diagram of the detection principle of the wavelength interrogation SPR sensor; (b) wavelength interrogation SPR imaging system^[28] (L1‒L3: lens; CL1 and CL2: cylindrical lens)

Fig. 6. Phase interrogation SPR sensors. (a) Phase interrogation SPR sensor based on Wollaston prism^[32]; (b) schematic of phase interrogation SPR biosensor system^[36] (L1‒L2: lens; AOTF: acoustic optics tunable filter; P1 and P2: polarizer; WP: custom wave plate, which can produce an optical path difference of 10⁵ nm for its s- and p- component; LCOF: liquid core optical fiber; CMOS: complementary metal-oxide-semiconductor camera)

Fig. 7. Goos-Hänchen shift interrogation SPR sensor. (a) Schematic diagram^[39]; (b) structural diagram of the device^[40]

Fig. 8. Finite element simulation of spherical AuNP coupling to the sensing film^[44]. (a) Electric field distribution after coupling AnNP (diameter is 40 nm, distance from the Au film is 5 nm); (b) electric field distribution (y=0) after coupling AuNP with different diameters; (c) electric field distribution (y=0) at different distances between AuNP (40 nm in diameter) and the Au film; (d) electric field distribution without AuNP (y=0)

Fig. 9. Detection method based on multiple amplification strategy. (a) Schematic diagram of miRNA detection based on super sandwich structure^[53]; (b) schematic showing the detection procedure of the 2D MXene-based SPR biosensor^[57]

Fig. 10. Schematic diagram of the exosomal miRNA detection using SPRi biosensor^[60]. (a) Self-assembly of DTF; (b) synthesis of ssDNA-functionalized AgNC; (c) self-assembly of Au-on-Ag heterostructures on the SPRi chip; (d) extraction and detection of exosomal miRNA

Fig. 11. Schematic diagram of estradiol detection^[66]

Fig. 12. SPR biosensor based on graphene sensitization. (a) SPR sensor based on the difference between ssDNA and dsDNA when binding with GO^[72]; (b) schematic diagram of dopamine sensing mechanism based on aptamers (the presence of dopamine leads to conformational changes in ssDNA aptamers)^[73]

Fig. 13. CK 19 detection with carboxylated graphite oxide^[76]

Fig. 14. Schematic illustration of the SPR biosensor based on GO-AuNPs composites^[79]

Fig. 15. Schematic diagram of graphene-MoS₂ enhanced SPR biosensor^[80]

Fig. 16. SPR biosensors based on 1L GB-rich WS₂ films^[86]. (a) Schematic diagram; (b) the result of detecting RdRp

Fig. 17. Fabrication and detection principle of an miRNA sensor integrated with antimonene nanomaterial^[91]

Fig. 18. SPR detection device based on Fabry-Pérot cavity and AuNRs^[92]. (a) Nanorods array combined with a cavity; (b) phase shifts occurring at one roundtrip of an electromagnetic wave in the nanorod-microcavity combination; (c) scanning electron microscopy picture of the bare nanorods; (d) scanning electron microscopy picture showing nanorods at Bragg distance in front of a gold mirror

Fig. 19. Schematic diagram of SPR biosensor detection based on Fabry-Pérot cavity^[95]

Fig. 20. Label-free detection of SARS-CoV-2 pseudovirus with an SPR sensor with nanopores^[100]