miRFP2 is a monomeric near infra-red fluorescent protein with an excitation peak of 676nm and an emission peak of 706nm in vitro. It is an artificial derivative of the naturally occurring fluorescent protein encoded by the Rhodopseudomonas palustris RpBphP1 gene, derived by mutagenesis of miRFP. In order to fluoresce, miRFP2 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) (FBrf0252733).