Plasmonic silver nanospheres embedded ε-caprolactone/reduced graphite oxide nanolayers as active SERS substrates

Label-free, sensitive, compatible and non-invasive nature of surface enhanced Raman spectroscopy (SERS) had substantially influenced various biological applications such as cell investigations, analysis of biomolecules such as DNA, RNA, proteins and detection of biomarkers for various diseases. This renders the engineering of bio-compatible, sensitive and efficient SERS substrates a necessity. In this study, the SERS activity of plasmonic silver nanospheres embedded ε-caprolactone/reduced graphite oxide nano layers (AGP) has been analyzed. The interactions of the nanolayers with nanospheres were evidenced by the broadening of the SPR band observed in UV-visible spectroscopy. Formation of AGP was further affirmed through X-ray diffraction patterns, X-ray photoelectron spectroscopy and the transmission electron microscopic images. Rhodamine 6G, a widely used SERS label for biological samples such as DNA and RNA sensing, protein screening, etc., was used here as the probing molecule to determine the efficiency of AGP as a SERS substrate. A low detection limit of 10^-6 M was achieved with a calculated SERS enhancement factor of 1.2 × 10⁸. The formation of 'hotspots' at the nanogaps between Ag nanospheres and the 'hot surfaces' on the nanolayers along with the efficient suppression of fluorescence, synergistically result in the enhanced Raman signals. This suggests the feasibility of developing AGP as a biocompatible, robust and efficient SERS substrate towards bio-sensing, molecule detection, etc.