From molecular to nanoplastic SERS detection: insights into the role of analytes in plasmonic substrate design

Nanoplastics are nowadays a significant subject of interest due to their potential negative impact on human health and environmental quality. Their submicron size necessitates innovative analytical techniques like surface-enhanced Raman scattering (SERS), which proves highly effective in trace molecular detection within the nanometer range. Although SERS technology has advanced significantly, there is a largely unexplored gap between demonstrating the efficiency of SERS substrates with probe molecules and the practical use of these substrates for nanoplastic detection. Therefore, this study explores whether the optimization of a specific SERS substrate towards molecular analytes is also valid for the detection of individual nanoplastics. Since SERS relies on materials with nanoscale features, here we present a new class of nanostructured SERS substrates with different surface morphologies and tuned plasmonic response fabricated by the colloidal lithography technique. In this regard, we first performed the SERS enhancement characterization of the plasmonic substrates functionalized with a molecular analyte (benzenethiol) by wavelength-scanned surface-enhanced Raman scattering measurements in the near-infrared spectral range. Furthermore, we investigated the SERS performance of the substrates for the detection of individual polystyrene spherical nanoplastic particles and the experimental results were corroborated with finite-difference time-domain (FDTD) analysis. The results indicate that while a SERS substrate optimized for molecular analytes may show excellent efficiency, separate optimization is necessary for efficient detection of individual nanoplastic particles.