MOF-on-MOF multi-enzyme cascade sensor for visual monitoring of uric acid in body fluids

The detection of biomarkers is of great significance in the assessment of physical condition and disease progression. Developing rapid reliable biomarker detection technologies is necessary to meet the increasing health monitoring demands. Here, we developed an ultrasensitive sensing system for determining uric acid (UA), constituted by the metal-organic frameworks structure MIL-100(Fe)@MOF-Tm. The sensing mechanism is based on the enzymatic oxidation reaction catalyzed by uricase. Owing to the ideal loading capacity, the as-designed MOF-on-MOF system could load plentiful uricase to maximize the enzymatic reaction effect. The possible catalytic enhancement triggered by surface metal sites enables ultrasensitive and efficient response to the target analyte. With increasing UA concentration, uricase loaded on the MOF structure generates allantoin and H 2 O 2 . The Fe 3+ is reduced and undergoes the Fenton reaction, promoting the conversion from o -phenylenediamine (OPD) to 2,3-diaminophenazine (DAP). Consequently, the sensor changes from blue to yellow fluorescence under UV and becomes deep yellow from colorless under natural light, respectively, achieving dual-model visual detection. Thanks to the reusable feature and stability, this sensor could be distinguished from other one-time probes with extraordinary reusage, selectivity, and low detection limit (3 nM) to UA. For the inherently suitability for constructing devices, the paper-based sensor and hydrogel sensing patch were developed and applied in multiple real samples detecting. This study formulates a reliable strategy for quantitatively monitoring UA, and furnishes new avenues for personal medical sensors.