Fig. 1. Main materials and application fields of flexible SERS substrate

Fig. 2. Schematic diagrams for preparing SERS paper substrates with different methods. (a) Flexible SERS platform was prepared on cellulose paper by impregnation method^[28]; (b) schematic diagram of Au@ZIF-8 SERS paper manufacturing process^[29]; (c) FE-SEM images of the filter paper substrate before and after the attachment of nanoparticles^[30]; (d) flexible AgFPs substrate production process diagram^[31]

Fig. 3. Schematic diagrams of preparing SERS paper substrates with different methods. (a) Schematic diagram of preparing SERS substrate with ink-jet printing method^[33]; (b) schematic of preparing silver nanowire array with automatic writing method and the nanowire array detection^[35]; (c) preparation plan of filter paper before and after hydrophobic modification^[36]; (d) schematic diagram of nanoparticle droplet self-assembly on PTTG, a typical photograph of paper-tip with AgNP accumulating at the paper-tip front, and a typical SEM image of the paper-tip SERS substrate^[37]

Fig. 4. Schematic diagrams of SERS substrates preparation based on cellulose. (a) Schematic diagram of SERS Q-tip making process^[39]; (b) preparation schematic diagram of mAu@AgNW@TEMPO-CNF nanopaper^[45]; (c) schematic diagram of a flexible SERS chip for the determination of H₂O₂^[46]

Fig. 5. Schematic diagrams of SERS substrates preparation based on polymer. (a) Schematic diagram of 3D Au@PDMS SERS substrate preparation and SERS detection of pesticide residues^[57]; (b) fabrication process diagram of flexible SERS chip^[58]; (c) schematic diagram of PAAN substrate preparation and uric acid detection in tears^[55]; (d) schematic diagram of preparation of bionic SERS substrate^[59]

Fig. 6. Schematic diagrams of SERS substrates preparation based on other flexible materials. (a) Schematic diagram of ACCE-MIM synthesis^[75]; (b) diagnostic schematic diagram of gefitinib and ritonavir based on AgNWs-AgNCs activated hydrophilic SERS chip supported by complex viscous matrix^[76]; (c) demonstration diagram of liquid sample collection by SERS sensor based on gloves^[77]; (d) chemical description of AgNPs/cicada substrate preparation process and SERS measurement diagram^[78]

Fig. 7. Applications of flexible SERS substrate in virus detection. (a) Schematic diagram of SERS biosensor using flexible polylactic acid membrane fabric prepared by electrospinning for detection of low concentration respiratory tract transmission virus in vitro and in vivo^[79]; (b) schematic diagram of monitoring SARS-CoV-2 spike protein with noble metal-free SERS sandwich immune structure based on VP@ZIF-67 porous array and BPNSs^[80]; (c) label-free detection platform combined SERS with machine learning^[81]

Fig. 8. Applications of flexible SERS substrate in wearable sensing technology.(a) Schematic diagram of a bifunctional contact lens sensor consisting of an antiprotein structure for IOP monitoring and a peptide-functionalized AuNBs SERS substrate for MMP-9 detection^[82]; (b) plasma metamaterial integrated wearable SERS sensing device^[83]

Fig. 9. Application of flexible SERS substrates in microfluidic devices. (a) Schematic diagram of the wearable plasma paper microfluidic device^[84]; (b) thread embroidered fabric sensor belt and its interface with the skin, as well as the display of the belt on the different areas of the human body^[85]

Fig. 10. Application of flexible SERS substrates in food safety. (a) SERS paper base synthesis route^[91]; (b) SF-AAO-Au SERS sensors on laboratory gloves for practical field pesticide residue detection^[93]; (c) schematic diagram of fingerprint identification of food and illegal pigments in beverages through a portable Raman detector^[36]

Fig. 11. Applications of flexible SERS substrates in environmental monitoring. (a) Schematic diagram of MCS matrix fabrication and actual SERS detection process^[66]; (b) Cot/Ca-TiO₂ flexible substrate for rapid in-situ SERS detection of quinolone residues on fish body surface and in fish pond water and synchronous degradation in flowing fish pond water^[98]; (c) the scheme for forming SR by eddy current assembly method^[99]; (d) APHC preparation and TNT thermal enrichment diagram^[100]