Bright near-infrared genetically encoded voltage indicator for all-optical electrophysiology

We developed genetically encoded voltage indicators (GEVIs) using bright near-infrared (NIR) fluorescent proteins from bacterial phytochromes. These new NIR GEVIs are optimized for combination of voltage imaging with simultaneous blue light optogenetic actuator activation. Iterative optimizations led to a GEVI here termed nirButterfly, which reliably reports neuronal activities including subthreshold membrane potential depolarization and hyperpolarization, as well as spontaneous spiking, or electrically- and optogenetically-evoked action potentials. This enables largely improved all-optical causal interrogations of physiology.