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

Surface-enhanced\nRaman scattering (SERS) has emerged as a powerful\ntool for contamination detection. Fabricating efficient nanostructures\nwith hotspots for signal enhancement and concentrating diluted target\nanalyte molecules to the hotspots are critical for ultrasensitive\nSERS detection, which generally requires advanced instruments and\nintricate manipulations. Herein, we report a simple, low-cost, and\nhigh-efficiency paper device that can simultaneously concentrate the\nanalytes and generate SERS hotspots rapidly with the assistance of\nlaser-induced thermophoresis. After dropping the target- and plasmonic\nnanoparticle-containing solution on a paper substrate, the evaporative\ngradient created by the laser-induced thermophoresis can promote the\ndelivery of the analytes and plasmonic nanoparticles simultaneously\nto the tiny area of the laser spot, forming compact SERS hotspots\nto significantly amplify the analyte’s Raman scattering signals.\nThis convenient thermophoretic strategy can be accomplished rapidly\nwithin ∼4 min and exhibits more than 10<sup>4</sup>-times higher\nsensitivity than that without the assistance of laser-based thermophoresis.\nThis elegant paper device is successfully applied to the detection\nof contaminants such as pesticides and nanoplastics in fruit and water\nsamples, holding the potential to provide a simple, fast, and cost-effective\napproach for on-site detection of environmental contaminants.