Fabrication of gold nanostars for SERS detection of microplastics in water

Environmental contamination by microplastic particles has become a globally recognized issue, attracting increasing scientific and regulatory attention. In this study, a rapid and efficient method for detecting microplastics was developed using surface-enhanced Raman spectroscopy (SERS) combined with highly active substrates, enabling real-time monitoring and fast analysis. Gold nanostars (Au NSs) with sharp multi-branched structures were controllably synthesized using chloroauric acid (HAuCl₄), silver nitrate (AgNO₃), and ascorbic acid (AA). Their formation was achieved by regulating the anisotropic growth of gold via the underpotential deposition (UPD) of silver ions. The resulting Au NS colloid was then uniformly deposited onto a PVDF membrane through vacuum filtration, producing an Au NSs-PVDF substrate capable of both enriching and enhancing the SERS signal of microplastic particles. Finite-difference time-domain (FDTD) simulations using a trimer model of Au NSs confirmed that the observed Raman signal enhancement originates from abundant electromagnetic "hot spots" generated by the sharp branches and the high specific surface area of the nanostars. SERS measurements demonstrated that rapid analysis of both single-component and binary mixtures of polystyrene (PS), polyethylene (PE), polyethylene terephthalate (PET), and polyamide (PA) microplastics in aqueous environments can be completed within 10 min. Furthermore, the minimum detectable concentrations for single-component PET, PS, PE, and PA in lake water were 0.2 g·L^-1, 0.4 g·L^-1, 0.4 g·L^-1, and 0.4 g·L^-1 respectively, representing a significant improvement in detection efficiency.