Ultrafine VO-anchored 3D N-doped carbon nanocomposite with augmented dual-enzyme mimetic activity for evaluating total antioxidant capacity.

Total antioxidant capacity (TAC) can be evaluated by detecting the content of antioxidants, such as ascorbic acid, based on the enzyme-mimetic activity of nanomaterials. Herein, we fabricated a 3D-VO/NC nanocomposite using a self-templating strategy, which achieved ultrafine particles (∼2.5 nm), a porous carbon layer, large specific surface area (152.4 m/g), N-doping and heterogeneous structure. The strong catalytic activity of 3D-VO/NC resulted from the integrated effect between the ultrafine structure of VO nanoparticles and the 3D porous nitrogen-doped carbon framework, effectively increasing the number of active sites. This nanozyme presented a higher catalytic activity than its components or precursors in the nanocomposite (e.g., VN/NC, NC, VO, and VO/g-CN). ROS scavenging experiments confirmed that the dual enzyme-like activity of 3D-VO/NC (catalase-like and oxidase-like) resulted from their co-participation of ‧O, h and ‧OH, among which ‧O played a crucial role in the catalytic color reaction. By virtue of the 3D-VO/NC nanoenzyme activity and TMB as a chromogenic substrate, the mixed system of 3D-VO/NC + TMB + HO provided a low detection limit (0.03 μM) and suitable recovery (93.0-109.5%) for AA. Additionally, a smartphone-based colorimetric application was developed employing "Thing Identify" software to evaluate TAC in beverages. The colorimetric sensor and smartphone-detection platform provide a better or comparable analytical performance for TAC assessment in comparison to commercial ABTS test kits. The newly developed smartphone-based colorimetric platform presents several prominent advantageous, such as low cost, simple/rapid operation, and feasibility for outdoor use.