In Situ Fabricated Cu-Ag Nanoparticle-Embedded Polymer Thin Film as an Efficient Broad Spectrum SERS Substrate

Abstract

Thin films of polymer-metal nanocomposites can serve as efficient surface-enhanced Raman scattering (SERS) substrates; it would be highly advantageous if it can be fabricated by a cost-effective and facile protocol, and high enhancement factors (EF) can be realized for a range of excitation wavelengths, enabling sensitive detection of different analytes. Poly(vinyl alcohol) (PVA) thin films with embedded Cu-Ag nanoparticles are fabricated through a simple in situ procedure via stepwise formation of CuO-PVA and Cu-PVA; the fabrication is monitored through the different stages, by spectroscopy, microscopy, electron diffraction, and elemental analysis. Choice of the Cu-Ag combination is dictated by its broad plasmonic extinction, favorable cost factor, and chemical stability of the nanocomposite; the hydrogel character of PVA facilitates analyte absorption and contact with the nanoparticles, leading to efficient SERS. Cu-Ag-PVA thin film with an optimal composition is shown to display plasmonic extinction over an appreciable part of the visible range and to provide EF of the order of 107-108 for the analytes, rhodamine 6G and methylene blue, at three different excitation wavelengths; the EF values are significantly higher than those reported earlier, with most of the Cu-Ag based SERS substrates. The novel polymer-bimetal nanocomposite thin film is an efficient SERS substrate providing subpicomolar limits of detection.