Direct On-Analyte Fabrication of Au Nanoparticles for Substrate-Free SERS Detection of Micro and Nanoplastics.

Detection of micro- and nanoplastic particles at extremely low concentrations in complex matrices is a critical goal in environmental science and regulatory frameworks. Surface-enhanced Raman spectroscopy (SERS) offers unique advantages for detecting molecular species in such mixtures, relying solely on their characteristic fingerprints. However, its application for plastic particles has been constrained due to weak analyte-substrate interactions. Here, we demonstrate a fabrication proof of concept where gold nanoparticles are synthesized directly onto polystyrene (PS) beads, creating hybrid bead structures specifically designed as substrate-free digital SERS (dSERS). This approach allows direct optical detection of the bead fingerprint, highlighting the interplay between bead fabrication and detection. Based on these findings, we anticipate that substrate-free dSERS will emerge as the method of choice for reliable and ultrasensitive detection of a wide range of analytes, laying the groundwork for a "facial recognition-like" approach to plastic identification.