Light-guided SERS-active micromotor clusters for on-site detection of microorganisms.

Surface-enhanced Raman spectroscopy (SERS) provides ultrasensitive molecular fingerprinting, but conventional static SERS substrates are often limited by inefficient analyte capture and poor spatial controllability. Herein, we report a light-driven micromotor SERS detector based on silver-coated polystyrene microspheres (Ag@PS) for active, localized, and rapid biochemical sensing. The Ag@PS micromotors were fabricated through an electroless silver-plating strategy, forming a dense nanoparticle-like silver shell that provides abundant plasmonic hotspots for SERS enhancement. Under light irradiation, the micromotors exhibited reversible "on-off" locomotion, positive phototaxis, and pronounced light-induced clustering. The micromotors reached an average velocity of approximately 6 μm s⁻1 under 1.2 mW cm⁻2 irradiation and could be remotely guided toward target regions by moving the light spot. Benefiting from light-directed accumulation and intimate probe-analyte contact, the Ag@PS micromotor clusters enabled sensitive SERS detection of rhodamine 6G down to 10⁻⁸ M with good signal reproducibility. Furthermore, the platform achieved label-free in situ Raman detection of diverse microorganisms, including Paramecium, Spirogyra, Euglena, and Marimo, using handheld Raman systems. This work demonstrates a simple and programmable light-responsive micromotor SERS probe for active target enrichment and on-site biological analysis, offering a promising strategy for portable, real-time, and spatially controlled SERS detection.