2',7'-Difluorofluorescein diacetate

2',7'-Difluorofluorescein, also called Oregon Green 488 (OG488) dye is a bright, green-fluorescent dye with excitation ideally suited to the 488 nm laser line and useful for fluorescent labeling. It has a high extinction coefficient and fluorescence quantum yield and while it is pH insensitive in the physiological range, with a pKa of 4.6 it can be used to as a fluorescent indicator for intracellular pH and monitor pH changes in acidic organelles or pathways. OG488 is a fluorinated analog of fluoresceins. The absorption and emission spectra of OG488 perfectly match those of fluorescein. Because of the near match of the absorption maxima on proteins (~498 nm and ~512 nm) to the strong 488 nm and 514 nm spectral lines of the argon-ion laser, the Oregon Green 488 fluorphore is an important dye for both confocal laser-scanning microscopy and flow cytometry applications. Conjugates of OG488 are more photostable than those of fluorescein, allowing increased acquisition of photons before photodestruction of the dye and making it particularly a useful substitute for fluoresceins for fluorescence imaging applications. OG488 has a lower pKa (pKa = 4.7 versus 6.4 for fluorescein), making the fluorescence essentially pH insensitive in the physiological pH range. However, the pH sensitivity in the weakly acidic range (pH 4 to 6) also makes the dye useful as pH indicators for acidic organelles of live cells. This cell-permeable non-fluorescent 2',7'-Difluorofluorescein diacetate is cleaved by cellular esterases and oxidation, and converted to the highly fluorescent 2',7'-Difluorofluorescein.