Development of a Uricase-Free Colorimetric Biosensor for Uric Acid Based on PPy-Coated Polyoxometalate-Encapsulated Fourfold Helical Metal–Organic Frameworks

Developing a new cost-effective and reliable approach used for the detection of uric acid (UA) with no requirement of uricase is still very challenging. Herein, an easily realized, cost-effective, and uricase-free approach is reported for selective colorimetric biosensing of UA utilizing polypyrrole (PPy)-coated polyoxometalate-encapsulated fourfold helical metal–organic frameworks Ag₅[bimt]₂[PMo₁₂O₄₀]·2H₂O (Ag₅PMo₁₂) as a monolithic peroxidase mimic. It is demonstrated that the as-obtained Ag₅PMo₁₂@PPy possesses excellent peroxidase-like activity originated from the synergistic effect to induce catalytic oxidation of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to green oxTMB in the presence of H₂O₂. Then, the green oxTMB can be selectively converted to colorless TMB induced by UA; thus, UA can inhibit the catalytic oxidation of TMB. Based on these results, a uricase-free colorimetric biosensor for UA is achieved with a linear detection range of 1–50 μM and a detection limit of 0.47 μM. More importantly, the developed biosensor is suited for simple-operated and good reliable UA detection in clinical samples, showing promising application ability in clinical diagnosis and relative fields.