An ESIPT-based two-photon fluorescent probe detection of hydrogen peroxide in live cells and tissues

A variety of diseases associated with human aging, which have a strong oxidative stress, but connecting age-related diseases and oxidative stress of the basic molecular mechanisms still insufficiently understood. Oxidative stress origins from the unregulated production of reactive oxygen species (ROS), and oxidative damaging to tissues and organs from subsequent oxidation-reduction chemistry by cellular mismanagement. In particular, H₂O₂ is a major by-product of ROS in live organisms and a common marker for oxidative stress, and its dynamic equilibrium can have various physiological and pathological consequences. H₂O₂ is a small molecule, but it is an essential oxygen metabolite in living systems and acts as an important compound in cellular signal transduction by reversible oxidation of proteins. To quantitatively detect of H₂O₂ in biosystems, herein, we adopted a 2-(2'-hydroxyphenyl)-4(3H)-quinazolinone (HPQ), a small organic fluorophore known for its luminescence mechanism through excited-state intramolecular proton transfer (ESIPT). HPQ was employed as a precursor to develop a turn-on probe (HPQ-H) for bioimaging applications. After cleavaging the boronic ester moiety by H₂O₂, HPQ-H releases a HPQ fluorophore which shows a 45-fold fluorescence intensity enhancement with high sensitivity and selectivity over other reactive oxygen species (ROS), and a high resolution imaging and large tissue-imaging depth (70-170μm) in living cells and tissues images under two-photon excitation (720nm).