Nickel Core-Thin Iridium Shell Nanoparticles as Cost-Effective and Highly Active Peroxidase-Mimicking Nanozymes

Peroxidase-mimicking nanozymes have emerged as powerful catalytic alternatives to natural enzymes for a wide range of applications. Among them, iridium (Ir)-based nanozymes exhibit exceptional intrinsic peroxidase-like activity. However, the high cost and scarcity of noble-metal Ir severely limit practical and large-scale use. Herein, we address this challenge by engineering a core-shell Ni-Ir nanozyme in which inexpensive nickel (Ni) serves as the core and catalytically active Ir forms a thin surface shell, resulting in a low Ir content of only 4.9 at.% (denoted as Ir_4.9%Ni). This architecture maximizes Ir utilization while preserving excellent catalytic performance. Importantly, the resulting Ir_4.9%Ni nanozyme was successfully applied as a catalytic label in both sandwich and competitive ELISA formats for sensitive detection of a prostate cancer biomarker and the food contaminant aflatoxin B1, respectively. In both assays, the nanozyme-based platforms outperformed conventional enzyme-based assays in analytical sensitivity. This work provides an effective strategy for engineering highly active yet cost-efficient nanozymes for bioanalytical and diagnostic applications.