Colorimetric acid phosphatase sensor based on MoO3 nanozyme

Nanozymes, or nanomaterials that mimic the behaviors of enzymes, are highly promising materials for biomedical applications because of their excellent chemical stability under harsh conditions, simple preparation method and lower costs compared with natural enzymes. We herein report the intrinsic oxidase-mimicking activity of molybdenum oxide nanoparticles (MoO3 NPs). MoO3 NPs catalyzed the oxidation of colorless 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) to green product. The catalytic mechanism of the oxidase-mimicking activity of the MoO3 NPs was investigated in detail using electron spin resonance and a radical inhibition method. The oxidation of ABTS stems from 1O2 generated from the interaction between MoO3 NPs and dissolved oxygen in the solution. Acid phosphatase (ACP) catalyzes the hydrolysis of the ascorbic acid 2-phosphate (AAP) substrate to produce ascorbic acid (AA). AA was found to fade the coloration process of the MoO3 NP-mediated ABTS oxidation. By combining the oxidase-mimicking property of the MoO3 NPs and the ACP-catalyzed hydrolysis of AAP, a novel and simple colorimetric method for detecting ACP was established. The linear range for ACP determination is 0.09-7.3 U/L with a detection limit of 0.011 U/L. This new colorimetric method was successfully applied to the detection of ACP in diluted human serum samples and screening of ACP inhibitors. The present study proposes MoO3 NPs as a new oxidase mimic for establishing various biosensing method.