A simple and rapid preparation of Au-Ag alloy nanourchins flexible membrane for ultrasensitive SERS detection of microplastics in water environment

Microplastic (MP) pollution has emerged as a significant environmental concern in aquatic ecosystems. Consequently, the development of rapid, sensitive, and efficient methods for microplastic detection is of paramount importance. This study presents a novel Au-Ag alloy nano-sea urchin (AAA-NUs) flexible membrane fabricated via a straightforward vacuum filtration technique. This membrane demonstrates high efficiency in enriching and detecting polyvinyl chloride (PVC) and polyethylene (PE) microplastics in water samples. Initially, an asymmetric seed-mediated growth method was employed to synthesize AAA-NUs with numerous sharp tips and rough surface morphologies, thereby creating abundant nano-interstices that enhance surface-enhanced Raman scattering (SERS) signals effectively. Subsequently, by employing a straightforward vacuum filtration technique, a substantial quantity of AAA-NUs can be rapidly and uniformly deposited onto the polytetrafluoroethylene (PTFE) membrane. This process facilitates the formation of stable surface-enhanced Raman scattering (SERS) “hotspots,” thereby significantly improving the sensitivity of the sensor. When water containing PE and PVC microplastics passes through the AAA-NUs membrane, these microplastics are captured efficiently. Leveraging the outstanding SERS enhancement of the AAA-NUs flexible membrane, this method achieves a low limit of detection (LOD) of 0.269 μg/mL and 0.373 μg/mL for PE and PVC, which was reduced by 1–2 orders of magnitude compared to conventional SERS substrates. With the growing prevalence of portable Raman spectrometers, this technology holds substantial promise for water quality assessment.