Ultrathin two-dimensional carbon nanosheets with highly active Cu-Nx sites as specific peroxidase mimic for determining total antioxidant capacity

We designed the Cu,N-codoped carbon (Cu-NC) nanosheets with highly active Cu-Nx sites through a facile nitrogen-doping strategy that employed copper MOF as a precursor and dicyandiamide as a N source, respectively. The Cu-NC displayed an ultrathin two dimensional sheet structure. The ultrathin nanosheet structure and Cu,N-codoping endowed Cu-NC highly exposed active sites. The Cu-NC showed superior and specific peroxidase-like activity able to greatly promote TMB oxidation by H2O2. Relative to that of Cu doped carbon (Cu-C) and N doped carbon (N-C), the peroxidase mimic activity of the optimized Cu-NC-700 increased by 19.06-fold and 15.84-fold, respectively. The mechanism investigation revealed that the ·OH is the main active oxygen specie for the peroxidase-like activity of Cu-NC-700. The Cu-NC-700 showed high affinity to TMB and H2O2 with Km values of 0.077 mM and 0.928 mM, which were 4.63 and 2.98 times lower than those of HRP, respectively. The high and specific peroxidase mimic activity enables the Cu-NC-700 for sensitively detecting H2O2, glucose, and ascorbic acid with limit detection of 10, 100 and 90 nM, respectively. The assay was successfully used to evaluate the total antioxidant capacity of real drinks.