Defect-engineered Pd@Cu/Zn/ZrO2/Pt core-shell nanodendrites with enhanced oxidase-mimicking catalytic efficiency for colorimetric immunoassay.

Oxidase-like nanozymes hold great potential for biomedical diagnostics; however, their low catalytic efficiency and poor anti-poisoning performance limit sensitive trace biomarker detection. Herein, we rationally designed and synthesized defect-engineered core-shell Pd@Cu/Zn/ZrO2/Pt alloy nanodendrites (NDs) by incorporating Zn doping-derived substitutional defects and amorphous ZrO2-induced oxygen vacancies. This dual-defect structure coupled with multi-metal synergy endowed the nanozyme with exceptional oxidase-mimetic activity, enhanced catalytic efficiency, and robust anti-poisoning ability. The catalytic constant ((Kcat) reached 9.23 × 105 s-1, which was 34-, 29-, and 5-fold higher than those of Pd@Cu/Pt, Pd@Cu/Zn/Pt, and Pd@Cu/ZrO2/Pt NDs, respectively. Mechanistic investigations revealed that oxygen vacancies activated O2 to produce singlet oxygen species (1O2) and superoxide anions (O2•-) as dominant reactive oxygen species for substrate oxidation. When applied in a colorimetric immunoassay for carcinoembryonic antigen, the proposed biosensor exhibited an ultralow detection limit of 5 pg mL-1, along with high specificity, satisfactory reproducibility, and good serum sample applicability. This work offers a feasible defect-engineering strategy for developing high-performance oxidase-like nanozymes in advanced biosensing and clinical diagnosis.