Silver coated porous alumina as a new substrate for surface-enhanced Raman scattering

Porous alumina filters were coated by vacuum deposition with silver metal and used as substrates for surface-enhanced Raman scattering (SERS). These were studied by UV-Vis absorption spectroscopy and scanning electron microscopy. The substrates exhibit reproducible Raman enhancement for different molecules tested in this study. The mass thickness of the silver was optimized for maximal SERS signal using bipyridine as a model compound. Plasma treatment or the substrates prior to SERS measurements was identified as a crucial factor for a low background and high signal-to-noise Raman spectra. The effect of different plasma treatment conditions on the SERS signal as well as on UV-Vis absorption spectra of the substrates was investigated. After the silver deposition, the porous alumina retained its filtering abilities and could be used for preconcentrating dilute analytes on the substrate surface for SERS measurements. Corresponding tests were performed using benzotriazole and bipyridine solutions. These substrates demonstrate a potential for large-scale applications in different analytical measurements.