Accelerated Mimetic Oxidase Activity of Polydopamine-Dressed PdCu Nanozyme for the Detection of Ascorbic Acid Related Bioenzymes

The spontaneous accumulating nature and undesirable catalytic activity of nanosized noble-metal nanoparticle-based nanozymes significantly limit their applications in the bioanalytical field. Herein, by combining surface modification and nonprecious metal doping strategies, polydopamine-dressed PdCu alloy (PDA-PdCu) nanozymes with nanochain networks are successfully prepared through a facile one-pot NaBH4 reduction method. It is found that dopamine can shorten the gel formation time and Cu is indispensable for the formation of jelly-like PDA-PdCu samples with chain-like structures. Notably, benefiting from the improved Pd(0)/Pd(II) ratio, the enhanced substrate affinity, and the increased active surface area, the synthesized PDA-PdCu samples exhibit considerably enhanced oxidase mimetic activity compared to PDA-Pd and PdCu nanozymes. By making full use of the enhanced oxidase-like activity of PDA-PdCu and using 3,3′,5,5′-tetramethylbenzidine as a chromogenic substrate, a sensitive and straightforward colorimetric biosensing strategy for ascorbic acid (AA)-related bioenzyme activity, including the AA-generating alkaline phosphatase (ALP) and α-glucosidase (α-Glu) as well as the AA-consuming ascorbic acid oxidase (AA-ox), is elaborately developed. This work not only elucidates that the performance of the nanozyme can be modulated simultaneously by composition and surface modification but also provides a new versatile colorimetric sensing platform for AA-related bioenzymes.