Spontaneous Capture, Enrichment, and SERS Sensing of Polystyrene Micro/Nanoplastics Enabled by Condensed Plasmonic Coacervate Droplets

Pervasive contamination by micro/nanoplastics (MNPs) poses threats to environmental and human health; however, their sensitive detection is challenged by low concentrations and lack of effective enrichment methods. Herein, we present a plasmonic coacervate platform that spontaneously sequesters polystyrene (PS) MNPs from water while facilitating surface‐enhanced Raman scattering (SERS) detection. Coacervate microdroplets, formed through the liquid–liquid phase separation (LLPS) of cationic poly(diallyldimethylammonium chloride) and anionic adenosine triphosphate, exhibit a positive surface charge and a hydrophobic interior, enabling capture of nanoscale or microscale negatively charged PS MNPs with enrichment rates of 99.4% and 91.1%. The co‐encapsulation of silver nanoparticles (AgNPs) generates three‐dimensional droplet‐confined SERS hotspot networks, resulting in an enhancement factor of 2.72 × 10 9 , excellent uniformity, and minimum detectable concentration of 1 and 10 ng/mL for nano‐ and micro‐scale PS, demonstrating strong linear correlations. This platform achieves recoveries ranging from 87% to 108% for PS MNPs spiked into filtered tap and river water and successfully detects PS MNPs released from commercial plastic cups and expanded polystyrene containers under simulated daily use. Our work establishes a simple, rapid, and sensitive strategy that integrates spontaneous analyte sequestration with plasmonic amplification, thus offering a new avenue for monitoring MNPs and assessing the safety of food‐contact materials.