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

ABSTRACT 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.