Pyranine (HPTS)

Pyranine (HPTS) (8-Hydroxypyrene-1,3,6-trisulfonic acid) is a highly water-soluble, membrane-impermeable pH fluorescent indicator with a pKa of approximately 7.3 in aqueous buffer^[1]. The maximum excitation wavelength of Pyranine (HPTS) is 405nm/450nm, and the maximum emission wavelength is 510nm^[2]. Pyranine (HPTS) has different fluorescence spectra in the protonated and deprotonated forms^[3]. The excited state of Pyranine (HPTS) is much more acidic than the ground state, and can be used as an excited state proton transfer probe in solution^[4]. Pyranine (HPTS) can be used as a new type of Cu⁺ fluorescent chemotaxis sensor, and its sensing properties are specific only to neutral pH^[5]. Pyranine (HPTS) is sensitive to the fluorescence quenching of viologen, which can be reversed in the presence of glucose or other monosaccharides, and can be used as a glucose and carbohydrate sensor^[6].

References:
[1] Lemos S. Acoustic" Wall-Less" Test Tubes for Cell Biology in Type 2 Diabetes Related Research[D]. Universidade da Beira Interior (Portugal), 2008.
[2] Chowdhury R, Saha A, Mandal A K, et al. Excited state proton transfer in the lysosome of live lung cells: normal and cancer cells[J]. The Journal of Physical Chemistry B, 2015, 119(6): 2149-2156.
[3] de Nooijer L J, Toyofuku T, Oguri K, et al. Intracellular pH distribution in foraminifera determined by the fluorescent probe HPTS[J]. Limnology and Oceanography: Methods, 2008, 6(11): 610-618.
[4] Wang Y, Fang C. Femtosecond Stimulated Raman Spectroscopy (FSRS) Investigation of Excited-State Hydrogen-Bonding Dynamics and Photoacidity in Solution[M]//Hydrogen-Bonding Research in Photochemistry, Photobiology, and Optoelectronic Materials. 2019: 323-367.
[5] Saha T, Sengupta A, Hazra P, et al. In vitro sensing of Cu+ through a green fluorescence rise of pyranine[J]. Photochemical & Photobiological Sciences, 2014, 13: 1427-1433.
[6] Cappuccio F E, Suri J T, Cordes D B, et al. Evaluation of pyranine derivatives in boronic acid based saccharide sensing: Significance of charge interaction between dye and quencher in solution and hydrogel[J]. Journal of Fluorescence, 2004, 14: 521-533.