A Turn-On Fluorescent and Ratiometric Electrochemical Dual-Mode Probe for Hydrogen Peroxide Detection in Brain Microdialysates of Alzheimer’s Disease Mice

Hydrogen peroxide (H2O2), a pivotal reactive oxygen species (ROS), is closely linked to oxidative stress in the pathogenesis of Alzheimer’s disease (AD). Herein, we report a dual-mode probe (Re-PS) integrating turn-on fluorescence and ratiometric electrochemistry for the selective detection of H2O2 in brain microdialysates of AD model mice. The probe is constructed using resorufin (Re) as a dual-signal reporter and a pentafluorobenzenesulfonyl (PS) group as the H2O2-responsive unit. Upon reaction with H2O2, the PS group undergoes nucleophilic substitution, leading to the release of Re; this process triggers a fluorescence “turn-on” response and generates a ratiometric electrochemical signal. Compared with ester-based probes, Re-PS shows superior stability due to the strong electron-withdrawing effect of fluorine atoms in the PS group. The fluorescence mode achieves a detection limit (LOD) of 50 nM, while the electrochemical detection mode (using a carbon fiber microelectrode modified with carbon nanotubes (CFME/CNT)) has a detection range of 1.0–50 μM. Both modes exhibit excellent selectivity against other ROS and biomolecules. In vivo microdialysis analysis reveals significantly elevated H2O2 levels in the brains of AD mice (28.6 ± 3.2 μM) compared with wild-type mice (10.3 ± 1.8 μM). This dual-mode strategy enables cross-validation, providing a reliable tool for monitoring oxidative stress in neurodegenerative diseases.