NirFP (scientific name eqFP670) is a red-shifted variant of TurboFP635 (Katushka) [Shcherbo et al., 2010]. NirFP is characterized by a strong bathochromic shift, with excitation and emission peaks at 605 nm and 670 nm, respectively. It is currently the most red-shifted fluorescent protein available, with approximately half of emission falling in the infrared part of the spectrum. The brightness of NirFP in the 700 – 900 nm region upon excitation at 635 nm is about 4 times higher than the brightness of TurboFP635 and 1.6 times higher than the brightness of TurboFP650. The protein does not show residual short wavelength fluorescence of intermediate or alternative chromophore forms, in contrast to E2-Crimson [Strack et al., 2009], which exhibits a second bright blue emission peak, and mNeptune [Lin et al., 2009], which has a pronounced green peak.

NirFP is characterized by high pH stability and extremely high photostability that should allow for accumulation of the fluorescent signal over long exposure times.

NirFP is recommended for multicolor applications. It can also be used for whole body imaging utilizing long wavelengths for excitation (e.g., 633 or 635 nm laser lines).