A novel colorimetric method for H2O2 sensing and its application: Fe2+-catalyzed H2O2 prevents aggregation of AuNPs by oxidizing cysteine (FeHOAuC).

The inhibition of hydrogen peroxide (H2O2) on the cysteine-mediated aggregation of gold nanoparticles (AuNPs) has great potential to rapidly visualize H2O2 and disease-associated biomarkers. However, associated applications have been rigid due to the low cysteine-oxidation efficiency or the insufficient interference-resistance of previous catalysts. Here, we proposed a novel AuNPs colorimetric method termed Fe2+-catalyzed H2O2-preventing aggregation of AuNPs by oxidizing Cysteine (FeHOAuC) for the visible and rapid detection of H2O2 with high specificity. Formed Fe2+-cysteine composites in the beginning, Fe2+ accelerates the oxidation of cysteine by H2O2 with an intramolecular electron-transferring model, and the generated cysteine oxides (including cysteic acid or cystine, dependent on the ratio of cysteine to H2O2 molecules) lose the pro-aggregation effect on AuNPs. Notably, FeHOAuC can quantify 2-30 μM of H2O2 within 5 min, and the monitoring process works well with tolerance to the impact of dissolved oxygen. The FeHOAuC paired with lactate oxidase was successfully used for measuring lactic acids in real sweat samples with a practicable detection window (2-60 μM) and a low variable coefficient (<10%). In summary, FeHOAuC is a feasible platform for rapid and convenient detection of H2O2 and oxidase-specific substrates.