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.