Nanowell-enhanced Raman spectroscopy enables the visualization and quantification of nanoplastics in the environment

Abstract

Nanoplastics are persistent pollutants that can cause severe toxicity to mammals. To date, no technology could simultaneously capture nanoplastic chemical and morphological information while conducting quantitative detection. Surface-enhanced Raman spectroscopy (SERS) has shown outstanding performance in trace pollutant detection in addition to providing morphological information. Despite these capabilities, physical changes originating from distribution discrepancies of nanoplastics coming into contact with a SERS substrate yield poor reliability. Herein, by exploiting the coffee ring effect, we develop a novel nanowell-enhanced Raman spectroscopy (NWERS) substrate composed of self-assembled SiO₂ sputtered with silver films (SiO₂ PC@Ag). Under the coffee ring effect, numerous robust nanowells that can trap nanoplastics are formed, providing a uniform testing environment for nanoplastics. Surprisingly, single polystyrene nanoplastic particles down to 200 nm can be directly visualized on the NWERS substrates and a LOD of 5 ppm was achieved in bottled water, tap water, and river water. The newly developed NWERS methodology opens a way for ultra-highly consistent SERS substrate engineering and has great potential in nanoplastic detection.