Rate-Engineered\nPlasmon-Enhanced Fluorescence for\nReal-Time Microsecond Dynamics of Single Biomolecules

Single-molecule fluorescence has revealed a wealth of\nbiochemical\nprocesses but does not give access to submillisecond dynamics involved\nin transient interactions and molecular dynamics. Here we overcome\nthis bottleneck and demonstrate record-high photon count rates of\n>10<sup>7</sup> photons/s from single plasmon-enhanced fluorophores.\nThis is achieved by combining two conceptual novelties: first, we\nbalance the excitation and decay rate enhancements by the antenna’s\nvolume, resulting in maximum fluorescence intensity. Second, we enhance\nthe triplet decay rate using a multicomponent surface chemistry that\nminimizes microsecond blinking. We demonstrate applications to two\nexemplary molecular processes: we first reveal transient encounters\nand hybridization of DNA with a 1 μs temporal resolution. Second,\nwe exploit the field gradient around the nanoparticle as a molecular\nruler to reveal microsecond intramolecular dynamics of multivalent\ncomplexes. Our results pave the way toward real-time microsecond studies\nof biochemical processes using an implementation compatible with existing\nsingle-molecule fluorescence methods.