Optical tweezers (OT) can manipulate and apply pico-newton forces in 3 dimensions to dielectric microparticles and plasmonic nanoparticles using a tightly focused laser beam at the focus of an optical microscope. While a powerful technique, it has primarily been applied to study materials in aqueous environments like bacteria, proteins, and DNA. Here, we use optical tweezers as a tool to study and control the gold (Au) nanoparticle-solvent interface on the single particle level in both aqueous and organic solvent conditions. This work is performed with a home-built optical tweezer system that allows simultaneous measurement of particle movement and darkfield imaging of local surface plasmon resonance (LSPR). Our measurements confirm that LSPR frequency of a single Au nanoparticle, held in an optical trap, is sensitive to the refractive index of the solvent environment. Using measurements of trap stiffness, we demonstrate that significant particle heating can occur in organic solvents under trap illumination, as expected for lower thermal conductivity solvents. However, trap stiffness is sensitive to solvent viscosity. Stiffer trapping can be achieved in viscous conditions at lower laser power where heating is minimal. These observations suggest that optically trapped plasmonic nanoparticles can serve as local probes of heat or charger transfer at the Au-solvent interface. Using this combination of optical trapping and darkfield imaging, we selectively induce and characterize metal organic framework (MOF) growth on the single nanoparticle surface.

Probing chemical environments with optically trapped plasmonic nanoparticles

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.