MnTi bimetallic MOF as peroxidase mimic for colorimetric detection of acid phosphatase.

Sensitive and visual detection of acid phosphatase (ACP) is essential for clinical diagnostics. However, the analytical performance of current colorimetric assays is often restricted by the limited catalytic efficiency of conventional single-component nanozymes. To address this issue, we designed a highly active bimetallic metal-organic framework (MnTi-MOF) to serve as a robust peroxidase mimic. By introducing Mn2+ into the Ti-MOF structure, the natural electronegativity difference between the heterometallic nodes generates an internal electric field. This built-in field drives the efficient separation of electron-hole pairs, which works in tandem with the Fenton-like Mn2+/Mn3+ redox cycle to accelerate the production of reactive oxygen species in the presence of H2O2. Relying on the high peroxidase-like activity of MnTi-MOF, we developed an inhibition-style sensing platform for ACP with 3,3',5,5'-tetramethylbenzidine (TMB) as the chromogenic substrate. During the assay, ACP hydrolyzes its substrate to produce ascorbic acid (AA), which readily reduces the oxidized TMB and causes a quantifiable decrease in absorbance. The proposed method yields a linear range of 0.02-1 U/L with a low detection limit of 0.015 U/L, and it proved reliable for detecting ACP in bovine serum. This work not only confirms the great potential of bimetallic MOF nanozymes for constructing sophisticated biosensing platforms but also provides new design principles for developing detection methods for other biological molecules.