5(6)-Carboxynaphthofluorescein

5(6)-Carboxynaphthofluorescein (CNF) is a fluorescent NIR emitting pH indicator with red fluorescence at pH 9 (Spectral: Ex/Em: 598/668 nm). The fluorescence shifs to shorter wavelengths (Ex/Em: 512/567nm) at neutral or acidic pH environments. Spectral data: lambdaex=512nm, lambdaem=567nm (acid/neutral), lambdaex=598nm, lambdaem=668nm (basic). CNF shows good sensitivity in an alkaline pH range and it can be exploited in the construction of fiber-optic pH sensors. CNF has been used as an intravesicular pH probe for the colorimetric detection of activity, selectivity and cooperativity of ion channels. CNF has been used to design a luminescent probe for determination of pH, based on a Forster resonance energy transfer (FRET) system, combining a europium chelate as the donor and CNF as a pH sensitive acceptor. The FRET system enables referenced pH detection in an exceptional broad dynamic range from pH 3 to 9.