mScarlet is a monomeric red fluorescent protein with an excitation peak of 569nm and an emission peak of 594nm in vitro. It is an artificial fluorescent protein, derived by mutagenesis of a synthetic gene template ('mRed7') that was designed based on mCherry, several naturally occurring red fluorescent proteins and chromoprotein structural information. mScarlet has high brightness, quantum yield and fluorescence lifetime. It is especially useful as a fluorescence resonance energy transfer (FRET) acceptor in ratiometric imaging (PMID:27869816).