Fig. 3

a Photograph of Ag nanoparticle/glass SERS substrate; b–f optical microscopy images of a white paper sheet taken after consecutive depositions of the same Ag nanoparticle/glass SERS substrate showing presence of Ag nanoparticle residues for the first four depositions; g photograph of Ag nanoparticle/PDMS SERS substrate; h optical microscopy image of a white paper sheet taken after deposition of Ag nanoparticle/PDMS SERS substrate showing no trace residues of Ag nanoparticles