Pyranine (free acid)

Pyranine (HPTS; Solvent Green 7) free acid is a pH-sensitive fluorescent indicator. Pyranine free acid acts as a class of fluorescent chemosensor for the Cu⁺ ion. Pyranine free acid is used as a coloring agent, biological stain, optical detecting reagent, and pH indicator (Ex/Em = 450/510 nm)^[1][2][3]. In Vitro:Pyranine is capable of discriminating ranges of cations from the Cu⁺ ion, even in competing environment. Pyranine displays a rapid fluorescence response (t_1/2=1.66 min) towards the Cu⁺ ion, and the micromolar detection limit enables the detection of the ion in environmental samples. The observed stoichiometry of complexation between Pyranine and Cu⁺ is 2:1^[1].
The pH-sensitive fluorescent indicator Pyranine is studied to determine its usefulness as probes for the living cornea and anterior chamber. Adequate concentrations are reached in the cornea and anterior chamber after topical administration; measurements can be made by fluorophotometry for many hours. The pH is calculated by measuring the ratio of fluorescent intensity at two excitation wavelengths, I463/I404, a measurement which is dependent on pH but independent of the concentration of the fluorophore and other variables which can alter the intensity^[2].