Fig. 1. Schematic of the process of preparing paper-based SERS substrate by self-assembly technology

Fig. 2. SERS substrate and substrate characterizations. (a) Whatman No.1 filter paper; (b) EDS characterization analysis; (c) XRD characterization analysis; (d) 20-nm size silver sol; (e) 50-nm size silver sol; (f)(g) surface morphology and spacing statistical results of SERS substrate with different silver particle sizes

Fig. 3. Simulation analysis of electromagnetic field distribution of Whatman No.1 filter paper samples. (a) Schematic of simulation model; (b) 20-nm particle size; (c) 50-nm particle size

Fig. 4. SERS spectra of R6G with different concentrations for flexible SERS substrates prepared by silver particles with different particle sizes. (a) 20-nm particle size ; (b) 50-nm particle size

Fig. 5. Raman measurement results. (a) Raman Mapping test; (b) multi-molecular detection

Fig. 6. Soft property experiment of paper-based SERS substrate. (a) Different bending level; (b) repeated bending and stretching