Ratiometric two-photon fluorescent probe for imaging hydrogen peroxide during stroke-induced ferroptosis

Ischemic stroke, the second leading cause of death and fourth leading cause of disability worldwide, occurs when the blood supply to the brain is blocked. It initiates a programmed cell death through apoptosis, autophagy, and ferroptosis, which results in neuronal damage and brain injury. Ferroptosis—cell death characterized by the accumulation of iron due to lipid peroxidation and excessive generation of reactive oxygen species (ROS)—was recently identified as a major cause of nerve damage and is believed to be a vital pathological process after ischemic stroke. However, existing methods for in situ detection of ferroptosis are currently insufficient. Therefore, we constructed a series of hydrogen peroxide (H2O2—one of the major ROS) probes (QH2O2, MQH2O2, and BQH2O2) with quinoline derivatives as two-photon fluorophores and boronate as the recognition domain. Experimental results indicated that the linear response range of the probe MQH2O2 to H2O2 increased from < 10 to 300 μM as compared with the probe QH2O2. Moreover, the linear correlation coefficient also increased from 0.9012 to 0.999, indicating that the ratiometric fluorescent probe has built-in corrections for environmental interference, which allows a more accurate fluorescence analysis. Modification of the probe by connecting triethylene glycol monomethyl ether (BQH2O2) increased the lipophilic index of the probe to 2.01, which enhanced its ability to cross the blood–brain barrier. Therefore, the developed probe is useful for analyzing the H2O2 production during an ischemic stroke and its fluctuatation with ferroptosis.