Real‐Time Monitoring of the Binding/Dissociation and Redox States of a Single Transition Metal Ions

Fluorescence resonance energy transfer (FRET) between organic fluorophores is conventionally used to monitor binding/dissociation and conformational change of macromolecules. Here we use FRET between a cyanine dye and single transition metal ions (tmFRET) to monitor the binding/dissociation of transition metal ions to a synthetic polypeptide, and show that different transition metal ion species can be clearly distinguished based on their binding lifetimes and FRET efficiencies. Furthermore, we demonstrate that the redox state of cytochrome c can be successfully monitored at the single‐ion level using the tmFRET.