Optically trapped microspheres have been used to isolate and apply force to single molecules, to measure force-induced contour length changes, and as soft scanning probes for imaging fragile materials. Each of these applications would benefit from the information provided by optical absorption or force-detected spectroscopies performed on the sample in parallel. By coating microspheres with metallic nanoparticles, the optical polarizability can be greatly enhanced at the expense of increasing back-scattering that tends to degrade optical trapping stiffness. In this work, 1 micron diameter silica glass microspheres were coated with ~3-10 nm silver nanoparticles, and aliquots were collected at various time points during the reduction to sample a range of coating densities. The samples were characterized structurally using scanning electron microscopy and by measuring the corner frequency, scattering sensitivity, and diffusion constant in an optical trap. At the highest densities achievable by colloid chemistry methods, the resulting microspheres were no longer optically trappable. Under the conditions developed here, threshold behavior was seen with precipitation for 3-4 minutes to reproducibly provide ~35% coverage of silver while still allowing a majority of the microspheres to be stably optically trapped.

Synthesis and characterization of optically trappable silver nanoshells

ACS Spring 2022

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