The biology of highly reactive oxygen radical species is of great interest in many biomedical research disciplines, including neurodegeneration, aging, cancer, and infectious diseases.[1] There are a number of fluorescent reagents, such as 2,7-dichlorodihydrofluorescein (DCDHF), that can be used to detect free radicals, but they have significant limitations due to their facile oxidation by light and numerous non-radical oxidants such as hydrogen peroxide (H2O2). [2] HPF is a cell-permeable aromatic amino-fluorescein derivative that has little intrinsic fluorescence. [3] It undergoes oxidation only by highly reactive oxygen species (hROS) such as the hydroxyl radical, peroxynitrite, and hROS generated from a peroxidase/H2O2 system. It is inert to hypochlorite ion, nitric oxide, hydrogen peroxide (H2O2), superoxide, and other oxidants. Upon oxidation, HPF is converted to the highly fluorescent molecule fluorescein, with excitation/emission maxima of 490/515 nm, respectively, allowing the simple direct detection of highly reactive biological radicals.

Reference:
[1]. Matés, J.M., Pèrez-Gómez, C., and Nunez de Castro, I. Antioxidant enzymes and human diseases. Clinical Biochemistry 32(8), 595-603 (1999).
[2]. Hempel, S.L., Buettner, G.R., O'Malley, Y.Q., et al. Dihydrofluorescein diacetate is superior for detecting intracellular oxidants: Comparison with 2',7'-dichlorodihydrofluorescein diacetate, 5(and 6)-carboxy-2',7'-dichlorodihydrofluorescein diacetate, and dihydrorhodamine 123. Free Radical Biology & Medicine 27(1), 146-159 (1999).
[3]. Setsukinai, K.i., Urano, Y., Kakinuma, K., et al. Development of novel fluorescence probes that can reliably detect reactive oxygen species and distinguish specific species. J. Biol. Chem. 278(5), 3170-3175 (2003).