Fig. 4

a Photograph of set up used for SERS analysis of colored paper with Ag nanoparticle/glass SERS substrates; b SERS (blue line) and Raman (black line) spectra of BIC medium red pen square on paper, SERS spectrum of reference Rodhamine B dye (red line). Spectra were taken with bench Raman instrumentation at 514 nm illumination; c SERS (blue line) and Raman (black line) spectra of BIC crystal purple pen square on paper, SERS spectra of reference Rodhamine B (red line) and Crystal violet (pink line) dyes, 514 illumination; d SERS (blue line) and Raman (black line) spectra of BIC medium green pen square on paper, SERS spectrum of reference Blue38 dye (red line). Spectra taken with handheld Raman instrumentation at 785 nm illumination; e–f optical images of colored red and green colored squares after SERS analysis