Nonlinearity-modulated single molecule trapping and Raman scattering analysis.

Abstract

Single molecule detection and analysis play important roles in many current biomedical researches. The deep-nanoscale hotspots, being excited and confined in a plasmonic nanocavity, make it possible to simultaneously enhance the nonlinear light-matter interactions and molecular Raman scattering for label-free detections. Here, we theoretically show that a nanocavity formed in a tip-enhanced Raman scattering (TERS) system can also achieve valid optical trapping as well as TERS signal detection for a single molecule. In addition, the nonlinear responses of metallic tip and substrate film can change their intrinsic physical properties, leading to the modulation of the optical trapping force and the TERS signal. The results demonstrate a new degree of freedom brought by the nonlinearity for effectively modulating the optical trapping and Raman detection in single molecule level. This proposed platform also shows a great potential in various fields of research that need high-precision surface imaging.