SERS-Active Ag Nanoparticles on Porous Silicon and PDMS Substrates: A Comparative Study of Uniformity and Raman Efficiency

Silver-coated porous silicon and polydimethylsiloxane (PDMS) are systematically analyzed as substrates for surface-enhanced Raman scattering (SERS). They were selected as representative metal−dielectric nanostructures characterized by different morphology and substrate dielectric constant which is reflected in the electromagnetic near-field intensity spectra. The study is conducted using 4-mercaptobenzoic acid as probe molecule with the aim to compare the scattering efficiency and the homogeneity of the Raman signal on the selected substrates. A larger SERS enhancement is evidenced for the silicon-based plasmonic nanostructures (>106, despite the electronic off-resonant excitation of the analyte). On the other hand, the silvered elastomeric substrates, characterized by a good Raman efficiency, show good repeatability featured by a low inter- and intrasubstrate standard deviation of the SERS signal intensity, which make them suitable for quantitative analysis. The influence of the excitation wavelength on such properties is deeply discussed taking into account experimental results and 3D modeling.