iRFP713(V256C) is a dimeric near infra-red fluorescent protein with an excitation peak of 662nm and an emission peak of 680nm in vitro. It is an artificial derivative of the bacteriophytochrome encoded by the Rhodopseudomonas palustris RpBphP2 gene, derived by mutagenesis of iRFP713 (PMID:26725513). In order to fluoresce, iRFP713(V256C) requires a biliverdin cofactor to act as the chromophore. This can be supplied in a transgenic animal by including a transgenic construct that encodes a heme oxygenase (HO).