Genetically encoded FRET sensors to monitor intracellular Zn2+ homeostasis

We developed genetically encoded fluorescence resonance energy transfer (FRET)-based sensors that display a large ratiometric change upon Zn2+ binding, have affinities that span the pico- to nanomolar range and can readily be targeted to subcellular organelles. using this sensor toolbox we found that cytosolic Zn2+ was buffered at 0.4 nm in pancreatic beta cells, and we found substantially higher Zn2+ concentrations in insulin-containing secretory vesicles.