MoO₂ and N-Doped Carbon Nano-Octahedron Nanozymes for Sensitive Detection of Alkaline Phosphatase

As a typical biomarker for clinical diagnosis of diseases, alkaline phosphatase (ALP) plays a crucial role in regulating the dephosphorylation of biomolecules. Consequently, it is necessary to develop an effective and simple method for the determination of ALP activity. In this work, we report a catalytic reaction-based colorimetric method to monitor ALP activity by using a nanostructured MoO 2 @NP-doped carbon nano-octahedron (MoO 2 @NPC) as a favorable oxidase mimetic. Because the C–O bond generated in the nano-octahedron MoO 2 @NPC regulates the electronic valence state of Mo between +5 and +6, the as-prepared MoO 2 @NPC regular octahedron with good peroxide-like (POD-like) properties and colorless 3,3′,5,5′-tetramethylbenzidine dihydrochloride hydrate (TMB) can be catalyzed to dark-blue oxTMB. When ALP hydrolyzes the substrate AAP, the produced AA with a certain reducing ability can not only reduce oxTMB to TMB but also consume hydroxyl radicals (•OH) generated in the MoO 2 @NPC/H 2 O 2 /TMB system, which significantly inhibits the color reaction of TMB. On this basis, a simple and efficient colorimetric method for ALP was constructed based on carbon-based nanozymes. Furthermore, the system goes for the detection of ALP with high sensitivity for the first time. The linearity is good in the range of 0.5–30 U/L, and the detection limit was 0.02 U/L and had good stability and reproducibility. Reliable and accurate measurements of analytes in real samples were also validated by our analytical method, showing that it can provide a reliable, convenient, and efficient nanoplatform for clinical diagnosis of ALP activity.