Citric-Acid-Modified Iron–Titanium Dioxide Nanodots for Fenton Reaction-Driven MRI Contrast Enhancement of In Vivo Hydrogen Peroxide

Reactive oxygen species (ROS), including hydroxyl and superoxide radicals, play crucial roles in disease development and are recognized as indicators for cancer and inflammation. Although these radicals possess paramagnetism due to unpaired electrons, their high reactivity and low in vivo concentrations challenge MRI detectability. In this study, we utilized iron–titanium dioxide nanodots modified by citric acid (Fe-TiO2-CA) as catalysts in the Fenton reaction to efficiently convert hydrogen peroxide, a diamagnetic molecule, into paramagnetic hydroxyl radicals. This conversion maintained the concentration of hydroxyl radicals within the detectable range for MRI. Our results demonstrated that Fe-TiO2-CA significantly shortened the T1 relaxation time in H2O2 solutions. Importantly, this approach successfully enabled in vivo imaging of areas with elevated hydrogen peroxide concentrations typical of cancerous and inflamed tissues. These findings highlight the potential of Fenton reaction catalysts as innovative diagnostic tools for MRI-based detection of diseases with elevated hydrogen peroxide levels.