Stochastic protein interactions monitored by hundreds of single-molecule plasmonic biosensors.

We present a plasmonic biosensor based on hundreds of individual gold nanorods with single-molecule sensitivity that are simultaneously monitored in real-time within a dark-field microscopy setup. The approach allows for the statistical analysis of single-molecule interactions without requiring any labeling of the analyte. We study an antibody-antigen interaction and find that the waiting-time distribution is concentration-dependent and obeys Poisson statistics. The ability to probe hundreds of nanoparticles simultaneously will provide a sensor with a dynamic range of 7 decades in concentration and will enable the study of heterogeneity in molecular interactions.