Dynamic behavior of membrane protein provides critical information in molecular and cellular mechanisms. To have access to the mobility of a membrane protein, single-particle tracking has been advanced for the microscopic mechanism understandings. Among various molecular motions, however, only the lateral motion of the protein has been monitored due to the lack of in situ imaging tool enabling observation for rotation and vibration. Here, we developed plasmonic nanoparticles which can monitor rotational diffusion dynamics as well as lateral motion. This nanoparticle probe allows direct evidence and quantitative analysis of rotation dynamics, and furthermore, observation of conformation changes of proteins and the protein-protein interactions in live cells. This study provides an insight into the molecular mechanism regarding the intracellular signaling process.1
