Ultrasmall Iridium Nanoparticles as Efficient Peroxidase Mimics for Colorimetric Bioassays

In this work, we report a peroxidase mimic composed of iridium (Ir) nanoparticles with an average size of only 1.1 nm that are coupled to a tungsten suboxide (WO2.72) nanorod as support. Such a peroxidase mimic exhibited an area-specific catalytic efficiency as high as 1.5 × 104 s–1 nm–2, outperforming most existing peroxidase mimics of noble metals. As proof-of-concept demonstrations, the peroxidase mimic was applied to colorimetric immunoassays of carcinoembryonic antigen (a cancer biomarker) and aflatoxin B1 (a potent carcinogen), which provided substantially enhanced detection sensitivities compared to conventional enzyme-based assays.