On the importance of optical forces in surface-enhanced Raman scattering (SERS)

This contribution reports on the combination of optical tweezers with SERS spectroscopy of colloidal silver nanoparticles covered by thiophenol. The experimental design is based on two different laser beams, one used for Raman excitation (lambda = 514.5 nm) and one for optical tweezing (lambda = 830 nm). For a fixed Raman excitation power, the SERS signal from thiophenol is found to increase dramatically when the trapping laser is activated. This result is interpreted as a combination of two effects, an accumulation of nanoparticles in the optical trap and an optically induced aggregation of these nanoparticles.