Indexed on: 01 Jun '18Published on: 01 Jun '18Published in: Analytical Chemistry
Acidified extracellular pH (pHe) is directly related to various disorders such as tumor invasion and resistance to drugs. In this study, we developed two-photon-excitable emission ratiometric probes (XBH1-3) for the in situ measurement of pHe. These probes, based on benzimidazole and polar solubilizing groups, exhibited a strong two-photon-excited fluorescence and sensitive blue-to-green emission color changes with pKa values of 5.1-5.7. XBH1, containing carboxylic acid, stained the extracellular region in neutral media; it entered the cell under acidic media, thereby allowing a precise measurement of the extra- and intracellular pH values in the acidified tissue. XBH2, containing the sulfonate peripheral unit, facilitated monitoring of the pHe value only. Ratiometric two-photon microscopy imaging re-vealed that XBH1 can directly monitor the pH values both inside and outside the cells in colon cancer tissue, as well as the morphologi-cal aspect. This could be useful for cancer analyses and drug development.