10.1021/acsnano.5b05396.s003 Timothy T. Ruckh Timothy T. Ruckh Christopher G. Skipwith Christopher G. Skipwith Wendi Chang Wendi Chang Alexander W. Senko Alexander W. Senko Vladimir Bulovic Vladimir Bulovic Polina O. Anikeeva Polina O. Anikeeva Heather A. Clark Heather A. Clark Ion-Switchable Quantum Dot Förster Resonance Energy Transfer Rates in Ratiometric Potassium Sensors American Chemical Society 2016 potassium concentrations Ratiometric Potassium Sensors modulate indicator imaging potassium fluxes nanosensor sensor Fo quantum dot species tool quencher interaction 2016-04-18 12:51:55 Dataset https://acs.figshare.com/articles/dataset/Ion_Switchable_Quantum_Dot_Fo_rster_Resonance_Energy_Transfer_Rates_in_Ratiometric_Potassium_Sensors/3180844 The tools for optically imaging cellular potassium concentrations in real-time are currently limited to a small set of molecular indicator dyes. Quantum dot-based nanosensors are more photostable and tunable than organic indicators, but previous designs have fallen short in size, sensitivity, and selectivity. Here, we introduce a small, sensitive, and selective nanosensor for potassium measurements. A dynamic quencher modulates the fluorescence emitted by two different quantum dot species to produce a ratiometric signal. We characterized the potassium-modulated sensor properties and investigated the photonic interactions within the sensors. The quencher’s protonation changes in response to potassium, which modulates its Förster radiative energy transfer rate and the corresponding interaction radii with each quantum dot species. The nanosensors respond to changes in potassium concentrations typical of the cellular environment and thus provide a promising tool for imaging potassium fluxes during biological events.