A Single Polyoxometalate Nanozyme for Cross-Reactive Thiol Array Sensing via pKa-Driven and Enrichment-Synergistic Strategy

Glutathione (GSH), cysteine (Cys), and homocysteine (Hcy) are essential biothiols involved in redox homeostasis and cell signaling. Yet, their structural similarity poses a significant challenge for accurate discrimination in complex biological samples. Herein, we report a polyoxometalate nanozyme (Fe4P2W18) with an atomically precise structure synthesized via a mild one-step method. Benefiting from its negatively charged surface and multi-electron reduction centers, the nanozyme effectively enriches biothiols under acidic conditions and exhibits excellent peroxidase-like activity. By leveraging its stepped catalytic response across pH 3.5, 4.0, and 4.5, which amplifies the pKa-driven differences in the overall molecular charge and electrostatic properties of biothiols, we constructed a single-material three-channel colorimetric array sensor that generates cross-reactive fingerprints. This sensor achieves 100% discrimination accuracy for GSH, Cys, and Hcy within 5 min, with a detection limit of 0.1 μM. It enables quantitative detection of thiol concentrations between 1 and 50 μM and accurately identifies binary and ternary thiol mixtures. Furthermore, the sensor successfully distinguishes cell types (HUVEC, HeLa, A549) and discriminates serum samples from cardiovascular disease patients. This strategy eliminates the complexity of multi-material arrays while leveraging the well-defined structure of Fe4P2W18 to provide mechanistic clarity, offering a simple, rapid, and reliable tool for biothiol analysis and early disease diagnosis.