Ce-UiO-66 nanozymes with charge-regulated uricase-like activity for enzyme/reagent-free detection of uric acid

Designing highly performed uricase-like nanozymes through enzymatic-like colorimetric analysis system is of vital significance for the quantitative detection of uric acid (UA). Herein, series of Ce-UiO-66 nanozymes with different surface charges through the ligand engineering strategy were rationally designed and synthesized as efficient uricase mimics with tailorable uricase-like activities to catalytically convert UA into allantoin and H2O2. Importantly, by tuning the functional groups of 1,4-benzoic acid ligands, we explored the relationships between the surface charges of Ce-UiO-66-X (X = H, NO2, Br, CH3, and OH) nanozymes and their uricase-like activity. Among them, Ce-UiO-66-CH3 with the moderate surface charge exhibited optimal substrate adsorption and product desorption, displaying the highest uricase-like activity. Significantly, H2O2, as the product of UA oxidation, enabled Ce-UiO-66-CH3 itself as a dose-dependent chromogenic substrate of H2O2, giving a white-to-orange color evolution due to the Ce-UiO-66-CH3-to-CeO2 phase transition. Afterwards, a smartphone-assisted all-in-one enzyme/reagent-free biosensor based on Ce-UiO-66-CH3 was established for the precise visual detection of UA analysis, which was featured by a wide detection range (31–4000 µM), a high sensitivity (limit of detection: 8.9 µM), a rapid response (~ 3 min), a high structural stability, and a high anti-interference ability.