Oxygen-vacancy-rich CoO atomic layers as a nanozyme for highly sensitive antioxidant capacity evaluation

Metal oxide nanozymes hold significant promise as alternatives to natural enzymes, but their widespread use is limited by low catalytic activity and poor substrate specificity. To address this, we developed oxygen-vacancy-rich two-dimensional CoO atomic layers via controlled low-temperature pyrolysis under reduced oxygen partial pressure, a synthesis strategy that ensures high vacancy concentration while maintaining an ultrathin morphology, as confirmed by X-ray photoelectron spectroscopy and electron paramagnetic resonance. The introduced oxygen vacancies markedly enhance the peroxidase-like performance of V_o-CoO, resulting in a lower Michaelis–Menten constant and a higher catalytic turnover relative to pristine CoO. Density functional theory calculations further indicate that the vacancies reduce the adsorption energy of H₂O₂ and promote the desorption of H₂O molecules, elucidating the origin of the activity boost. Capitalizing on these properties, we constructed a highly sensitive and selective colorimetric sensor for ascorbic acid detection. The platform was successfully applied to quantify the total antioxidant capacity in complex real-world samples, demonstrating robust analytical utility. This work underscores defect engineering as a powerful approach for tailoring nanozyme activity and expands the scope of metal-oxide-based nanozymes in advanced sensing applications.