VO x Quantum Dots with Multienzyme-Mimic Activities and the Application in Constructing a Three-Dimensional (3D) Coordinate System for Accurate Discrimination of the Hydrogen Peroxide over a Broad Concentration Range.

The construction of efficient nanozyme with multienzyme activities in a simple way is vital for the wide biological and chemical applications. Generally, the mimic enzyme activities depend on their sizes, surface states, and materials types. Quantum dots (QDs), one type of zero-dimensional nanomaterials, are much appealing due to their abundant catalytically active surface deficiency. The vanadium oxide (VO x) is one special transition metal oxides possessing different valence states. Inspired by these views, we synthesized VO xQDs herein via a one-pot top-down ethanol-thermal method using bulk VO2 as the precursor. The VO xQDs showed not only oxidase- and peroxidase-like activities in ethanol as the main background solution (ethanol-BGS), but also exhibited additional superoxide dismutase mimetic activity in phosphate buffer solution. Furthermore, the TMB-VO xQDs system in the ethanol-BGS produced three distinct colors in the presence of hydrogen peroxide (H2O2) at three different concentration gradients (10-90 μM, 0.1-10 mM, and 20-100 mM). Accordingly, we constructed a three-dimensional (3D) coordinate system (3D-CS) by using the three variables: the initial velocities, the maximum absorption values and the visual colors of the enzymatic reaction system. As a result, the rapid detection of H2O2 can be achieved while effectively avoiding the faked appearance due to the inhibition effects to the enzymatic system at too high H2O2 concentration. The applicability of the VO xQDs based 3D-CS was further proved via the facile and accurate H2O2 assays in three different practical samples.