Superior oxidase-mimetic gadolinium vanadate nanoparticles for sensitive enzyme-free colorimetric detection of uric acid.

A novel, enzyme-free, colorimetric sensing platform for the sensitive and selective detection of uric acid (UA), based on the oxidase-mimetic activity of gadolinium vanadate (GdVO₄) nanoparticles is presented. The GdVO₄ nanozyme effectively catalyzed the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) into a blue-colored product, which was subsequently reduced by UA, resulting in a measurable decrease in absorbance at 655 nm. This assay provided a wide linear range (0.01-500 µM), a low detection limit (0.0023 µM), and a rapid response time (5 min). Mechanistic studies confirmed that reactive oxygen species (•OH, O₂•⁻, and ¹O₂) mediate the catalytic process. The platform showed favorable stability, reproducibility, and selectivity toward UA, even in the presence of common interferents. Moreover, the method was successfully applied to human serum samples, with recoveries ranging from 95.0% to 105.0%. A smartphone-assisted paper-based device enabled portable UA detection over a linear range of 5-460 µM with a detection limit of 1.38 µM. Collectively, these results establish GdVO₄ as effective nanozyme for simple, cost-effective, and portable colorimetric sensing of UA in clinical and point-of-care settings.