A donor-π-acceptor fluorescent probe for hydrogen peroxide monitoring reveals oxidative imbalance and mitochondrial damage caused by Cd/Hg exposure.

Heavy metal ions trigger hydrogen peroxide (H2O2) outbreak and sustained toxic damage, but current H2O2 fluorescent probes still suffer from critical limitations in revealing long-term oxidative stress under cadmium ion (Cd2+) and mercury ion (Hg2+) co-exposure, and are limited by narrow Stokes shift and insufficient sensitivity. Herein, an original donor-π-acceptor (D-π-A) push-pull electron transferring fluorescent probe, TQ-H2O2, was designed for clarifying the vague relationship between Cd2+/Hg2+-triggered up-regulated H2O2 overproduction, oxidative imbalance and cellular damage. Intrinsic fluorescence quenching was eliminated and the intramolecular charge transfer (ICT) mechanism restored upon addition of H2O2. The probe affords splendid responsive performance, including a large Stokes shift (119 nm), excellent sensitivity (LOD = 86.6 nM), distinctive specificity and decent biosecurity. TQ-H2O2 was employed to observe exogenous and endogenous H2O2 level fluctuations in RAW264.7 cells, HepG2 cells and zebrafish, and provided visual evidence of Cd2+/Hg2+-mediated H2O2 variation at the cellular level after exposure. Furthermore, the attenuation of the mitochondrial membrane potential (MMP) and the degree of cell damage under variant stimulation with Cd2+/Hg2+ were evaluated. This work establishes a reliable analytical method for visualizing H2O2 dynamics and clarifying the causal link between heavy metal-induced oxidative stress, mitochondrial dysfunction, and cellular damage, providing a powerful tool for environmental toxicology and risk assessment.