Autonomous DNA Nanoswitch Encodes Quantum-Yield Oscillations for Time-Resolved Single-Molecule Readout.

Precise control of fluorescence quantum yield at the single-emitter level is pivotal for molecular imaging and ultrasensitive detection, yet most plasmon-fluorophore studies rely on fixed gaps or ensemble averages, leaving autonomous, real-time tuning of an individual emitter via nanometal surface energy transfer largely unexplored. Here, we introduce an autonomous DNA-metallic nanoswitch that continuously modulates a single emitter's quantum yield by dynamically varying its separation from a gold nanoparticle. Programmable DNA hybridization acts as a molecular lever that shuttles the dye between a subnanometer "off" state ( < 1 nm), where nonradiative energy transfer quenches emission, and a multinanometer "on" state ( > 4 nm), where emission recovers; the resulting reversible oscillations follow the characteristic ∼1/d distance dependence. This distance-encoded operation yields robust self-blinking trajectories and time-domain metrics (on/off contrast and dwell times) even under high-background conditions. With built-in blinking, nanometer-scale positioning, and straightforward DNA addressability, the nanoswitch deepens understanding of metal-fluorophore coupling and provides a versatile platform for time-resolved single-molecule readout in imaging and diagnostics.