FlicR1 is a bright red fluorescent voltage indicator with fast kinetics. It is consists of the voltage sensing domain from the Ciona intestinalis VSP gene (GB:AB183035) fused after residue 242 via a linker sequence to a circularly permuted fluorescent protein that is based on mApple. A number of mutations have been introduced into the fusion protein (in both the voltage-sensing domain and the circularly permuted mApple sequence) relative to the starting template (PMID:26911693).