Highly exposed Cu active sites as efficient peroxidase mimics for colorimetric analysis

Nanozymes are nanomaterials with intrinsic enzyme-mimic activity, but their large-scale application is generally limited by their low catalytic activity. Herein, we demonstrated that highly exposed Cu active sites on two-dimensional (2D) nitrogen-doped carbon (Cu_x/NC) can serve as efficient peroxidase-like (POD) catalysts with high atomic utilization. Specially, the uniformly distributed Cu active sites could react with H₂O₂ to produce singlet oxygen (¹O₂) under acidic conditions, which can efficiently oxidizes colorless 3,3′, 5,5′-tetramethylbenzidine (TMB) to blue oxidized TMB (oxTMB). Among various Cu_x/NC nanozymes studied, the Cu_0.14/NC exhibited smaller maximum catalytic velocities (V_max) and Menten constant (K_m) for TMB and H₂O₂. Benefiting from the highly active peroxidase-like activity, the Cu_0.14/NC nanozyme could be successfully applied for the hydroquinone (HQ) and ascorbic acid (AA) detection applications through the inhibitory effect of HQ and AA. More interestingly, α-glucosidase (α-Glu) detection sensing platform could be constructed based on HQ as a signal transmitter, with the detection range ranging from 0 to 12 U/L and the minimum detection limit being 0.68 U/L. This work provides not only an idea for the rational design of highly exposed Cu active sites but also fabricate an effective detection sensing platform for HQ, AA, and α-Glu detection.