Combining CeVO oxidase-mimetic catalysis with hexametaphosphate ion induced electrostatic aggregation for photometric sensing of alkaline phosphatase activity.

In the present work, a novel alkaline phosphatase (ALP) activity colorimetric assay is proposed by integrating the oxidase-mimicking catalytic characteristic of CeVO nanoparticles with the hexametaphosphate ion (HMPi) mediated electrostatic aggregation. The CeVO nanoparticles exhibit good oxidase-mimetic catalytic ability to promote the 3,3',5,5'-tetramethylbenzidine (TMB) oxidation to TMBox, offering a significant change from colorless to blue. After a small amount of HMPi is added, the strong electrostatic interaction between the negatively charged HMPi species and the positively charged TMBox product leads to the aggregation of the latter, generating an aubergine HMPi-TMBox agglomerate. After the agglomerate is filtered out, the reaction solution turns to be almost colorless. When ALP is used to hydrolyze the HMPi species in advance, the electrostatic aggregation process is remarkably restrained, thus retaining the blue color of the CeVO catalyzed TMB solution. According to the new sensing strategy, highly selective and sensitive analysis of ALP activity was realized, providing a wide detection range from 1 to 210 U/L and a detection limit of 0.68 U/L. Accurate measurement of ALP activity in clinical serum matrices was also validated, demonstrating the practicability of the proposed assay in practical applications.