Semiconductor Heterojunction-AgNPs Mediated Surface-Enhanced Raman Spectroscopy (SERS) Sensor for Portable Miniaturized Detection Platform

Micro/nanoplastic pollution in the water environment has received great attention worldwide. The rapid identification and analysis of micro/nanoplastics are crucial steps for monitoring animal safety and protecting human health. Herein, we developed a novel surface-enhanced Raman spectroscopy (SERS) sensor based on Co3O4/Co3S4/AgNPs array substrate for the detection and analysis of micro/nanoplastics. The semiconductor heterojunction-induced charge transfer, enhanced together with the electromagnetic enhancement of plasmon AgNPs, endow the sensor with high sensitivity, thus achieving exceptional analytical and detection capability for polystyrene (PS) nanospheres of different sizes ranging from 1 µm to 1 nm. The limits of detection (LOD) for PS nanospheres (size of 1 µm and 800 nm) was as low as 25 µg/mL, even with a portable Raman spectrometer. Additionally, the periodic Co3O4/Co3S4/AgNPs array generated high repeatability of Raman signals with relative standard deviation (RSD) values less than 7.6%. As proof of this concept, we further demonstrated the simulation detection of PS in actual water samples. We measured the SERS spectra of the different sizes and concentrations of PS spiked in lake water and city water. The results showed that the sensing platform realized trace detection of PS nanospheres in lake water with a detection limit of 14 µg/mL, and a quantitative detection of PS with linear relationship (R2 = 0.962). This SERS sensor has demonstrated fast analysis of PS nanospheres, which can provide a solid basis for the qualitative and quantitative detection of various micro/nanoplastics in the real water environments.