Pyranine

Pyranine (HPTS; Solvent Green 7) is a cell-impermeant pH-sensitive fluorescent indicator. Pyranine acts as a class of fluorescent chemosensor for the Cu⁺ ion. Pyranine 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. In the rabbit eye, Pyranine in the cornea and anterior chamber is observed to undergo easily measurable changes in fluorescent ratios associated with lid closure and contact lens wear, indicating its sensitivity to mild changes in pH^[2].