Ratiometric and photoconvertible fluorescent protein-based voltage indicator prototypes.

To expand the toolbox of fluorescent protein-based voltage indicators, we explored two distinct protein design strategies. Using these design strategies, we created three new voltage indicators: a red intensiometric voltage indicator (tdFlicR Δ110AR), a green/red ratiometric voltage indicator (tdFlicR-VK-ASAP), and a green to red photoconvertible voltage indicator (FlicGR1).