Fig 3. Comparison of surface-enhanced Raman scattering (SERS) spectra of a non-thiol analyte (i; aniline), a thiol analyte (ii; 4-ATP) and their mixture (iii; same quantities of aniline and 4-ATP).

(a) Raman spectra of SiO₂@Ag NPs and (b) SiO₂@Ag@SiO₂ NPs. Raman spectra were obtained by 532 nm photoexcitation and 10s acquisition. Intensities were normalized to Raman intensity of the ethanol peak at 882 cm⁻¹. The characteristic aniline peaks were not detected in the spectrum of the mixture when the SiO₂@Ag NP SERS substrate was used. However, both peaks of aniline and 4-ATP were detected at similar intensities when the SiO₂@Ag@SiO₂ NPs was used as SERS substrate. Baselines were adjusted for the clarity of comparison.