  We present a palette of brightly fluorescent genetically encoded voltage
indicators (GEVIs) with excitation and emission peaks spanning the visible
spectrum, sensitivities from 6 - 10% Delta F/F per 100 mV, and half-maximal
response times from 1 - 7 ms. A fluorescent protein is fused to an
Archaerhodopsin-derived voltage sensor. Voltage-induced shifts in the
absorption spectrum of the rhodopsin lead to voltage-dependent nonradiative
quenching of the appended fluorescent protein. Through a library screen, we
identified linkers and fluorescent protein combinations which reported neuronal
action potentials in cultured rat hippocampal neurons with a single-trial
signal-to-noise ratio from 6.6 to 11.6 in a 1 kHz imaging bandwidth at modest
illumination intensity. The freedom to choose a voltage indicator from an array
of colors facilitates multicolor voltage imaging, as well as combination with
other optical reporters and optogenetic actuators.
