Laser-Induced Thermophoretic SERS Enhancement on Paper for Facile Pesticide and Nanoplastic Sensing

Surface-enhanced Raman scattering (SERS) has emerged as a powerful tool for contamination detection. Fabricating efficient nanostructures with hotspots for signal enhancement and concentrating diluted target analyte molecules to the hotspots are critical for ultrasensitive SERS detection, which generally requires advanced instruments and intricate manipulations. Herein, we report a simple, low-cost, and high-efficiency paper device that can simultaneously concentrate the analytes and generate SERS hotspots rapidly with the assistance of laser-induced thermophoresis. After dropping the target- and plasmonic nanoparticle-containing solution on a paper substrate, the evaporative gradient created by the laser-induced thermophoresis can promote the delivery of the analytes and plasmonic nanoparticles simultaneously to the tiny area of the laser spot, forming compact SERS hotspots to significantly amplify the analyte's Raman scattering signals. This convenient thermophoretic strategy can be accomplished rapidly within ∼4 min and exhibits more than 104-times higher sensitivity than that without the assistance of laser-based thermophoresis. This elegant paper device is successfully applied to the detection of contaminants such as pesticides and nanoplastics in fruit and water samples, holding the potential to provide a simple, fast, and cost-effective approach for on-site detection of environmental contaminants.