Sensitive SERS detection of PFOA and PFOS using silver-decorated graphene hydrogel substrates

Per- and polyfluoroalkyl substances (PFAS), such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), are persistent and harmful pollutants whose detection at trace levels is extremely challenging due to their amphiphilic nature, chemical inertness, and intrinsically low Raman scattering cross-section. Here, we present a novel PFAS detection method featuring silver nanostructures with strong surface-enhanced Raman scattering (SERS) activity that are electrochemically deposited on self-assembled graphene nanoplatelet (GNP) hydrogels. The morphology and plasmonic activity of the silver nanostructure on the GNP hydrogel scaffolds were studied as a function of deposition parameters, such as applied voltage, frequency, and deposition time. Optimal conditions (5 V at 5 Hz for 60 min) yielded branched silver nanostructures with high surface coverage (∼89.6%). The substrate demonstrated reproducible SERS performance, with a relative standard deviation of 6% for peak intensity across multiple substrates. Moreover, we introduce an electric field-assisted co-deposition strategy that facilitates analyte positioning at SERS hotspots, thus enabling reliable detection for both PFOA and PFOS down to 30 ppt. Experimental findings were supported by finite-difference time-domain (FDTD) simulations, offering insights into the synergistic electromagnetic enhancement provided by the hybrid dendritic-nanoparticle architecture. Overall, this work demonstrates a reproducible hydrogel-based SERS-active substrate with potential for on-site PFAS detection and monitoring.