Dynamic characterizations of biomolecules at nanomolar levels using optical-tweezers-coupled surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy (SERS) enables ultrasensitive detection through hotspots within metallic nanostructures. However, isolated nanoparticles provide limited enhancement. Herein, we developed a salt-free, reversible dual-trap optical tweezers-coupled SERS platform. This system utilizes optical trapping to manipulate silver nanoparticles (AgNPs), facilitating their collisions and generating dynamic hotspots to amplify the SERS signals of cortisol under various conditions. By comparing spectra under dual-trap, single-trap, and no-trap conditions, we found the signal was significantly enhanced between the two trapping beams, where AgNP collisions were optimized. This dual-trap SERS approach achieved a 10 nM cortisol detection limit, three orders of magnitude lower than non-trapped systems, reaching the physiological range. Hence, the dynamic control of nanoparticle collisions and assembly would advance label-free, ultrasensitive biomolecule detection for diagnostics and health monitoring applications.