Double nanohole optical trapping: dynamics and protein-antibody co-trappingElectronic supplementary information (ESI) available: Experimental results showing additional co-trapping events of BSA with anti-BSA. See DOI: 10.1039/c3lc00003f

A double nanohole in a metal film can optically trap nanoparticles such as polystyrene/silica spheres, encapsulated quantum dots and up-converting nanoparticles. Here we study the dynamics of trapped particles, showing a skewed distribution and low roll-off frequency that are indicative of Kramers-hopping at the nanoscale. Numerical simulations of trapped particles show a double-well potential normally found in Kramers-hopping systems, as well as providing quantitative agreement with the overall trapping potential. In addition, we demonstrate co-trapping of bovine serum albumin (BSA) with anti-BSA by sequential delivery in a microfluidic channel. This co-trapping opens up exciting possibilities for the study of protein interactions at the single particle level. Optical trapping of a single protein followed by co-trapping of its antibody is demonstrated using a double nanohole.