Ion-Switchable Quantum Dot Förster Resonance Energy Transfer Rates in Ratiometric Potassium Sensors

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.