PMC

Designs for genetically encoded voltage indicators. Examples are shown for different classes of voltage sensors based on voltage-sensing domains (left column) and microbial rhodopsins (right column). The upper half of the figure depicts sensors that require voltage-sensitive FRET between two fluorescent proteins (left) or a fluorescent protein and a rhodopsin (right). The bottom half of the figure shows sensors based on a single chromophore from a green fluorescent protein (left) or a rhodopsin (right). CFP, YFP, GFP and RFP are cyan, yellow, green and red fluorescent proteins, respectively. cpGFP, circularly permuted GFP. Protonation of rhodopsin's retinal Schiff base is depicted as a circled proton (H+). Intensity of fluorescence emission is depicted using the size of wavy arrows. For FPs, lower fluorescence emission is also shown with greyed-out rather than colored cylinders. Absorption and emission spectra are inspired by Ref. [,].