Direct observation of the orientation dynamics of single protein-coated nanoparticles at liquid/solid interfaces.

We have observed the rotational dynamics of single protein-coated gold nanorods (AuNRs) on C18-modified silica surfaces in real time by dual-channel polarization dark-field microscopy. Four different rotational states were identified, depending on the apparent strength of interactions between the AuNRs and the surface. The distributions of the states could be regulated by adjusting the salt concentration, and the state transitions were verified by monitoring the entire desorption process of a single AuNR. Our study provides insight into the interfacial orientation and dynamics of nanoparticles and could be useful for in vitro biophysics and the separation of proteins.