Transfer of silver nanoparticles (AgNPs) to dichloromethane for single-step and in-situ synthesis of PDMS-AgNPs nanocomposites for SERS analysis.

Silver nanoparticles (AgNPs) deposited in polydimethylsiloxane (PDMS) films has recently received significant attention for the fabrication of SERS substrates, but, conventional deposition of AgNPs on PDMS requires complex, additional post-synthesis steps. This work presents a novel, single-step, and in-situ synthesis of flexible PDMS films with incorporated AgNPs for Raman-SERS applications. The method involves an AgNPs phase transfer from aqueous colloid to a dichloromethane (DCM) organic phase, which is then used as the solvent during PDMS synthesis. UV-Vis spectroscopy results show a maximum transference using a minimum volume of DCM and centrifugation of the colloid. Given its historical and cultural relevance as a colorant in diverse artefacts and ancient codices made of cellulose paper, the common dye, annatto, impregnated in paper, was used as an analyte model to evaluate the SERS performance of PDMS-AgNPs films in Raman spectroscopy, using 785 and 532 nm lasers, along with different concentrations of aqueous annatto extracts (0.01, 0.1, 0.125, 0.25, 0.5, and 1% w/V). The results demonstrated a significant enhancement in the intensity of the characteristic peaks of bixin (the main component of annatto), especially in extracts of low concentration (0.125 and 0.25% w/V) when the PDMS-AgNPs nanocomposite films synthesized with the AgNPs transferred using a minimum volume of DCM and centrifugation were used.