Highly Active Carbon–Platinum-Based\nNanozymes:\nSynthesis, Characterization, and Immunoassay Application

Nanozymes (nanomaterials with intrinsic enzyme-like characteristics)\nhave gained much attention for diagnostics and therapy due to their\nexcellent enzyme-mimicking capability, great stability in environments,\nand facile and low-cost production. However, developing nanozymes\nwith a high catalytic constant, <i>K</i><sub>cat</sub>,\nhas been challenging. Herein, we report a class of nanozyme-mimicking\nperoxidases, which are formed by depositing ultrasmall platinum nanoparticles\n(Pt NPs) 1–2 nm in size on the surface of hydrophilic nitrogen-doped\ncarbon nanoparticles (CN NPs). These nanozymes defined as CN-Pt NPs\nshow a high peroxidase-like activity with <i>K</i><sub>cat</sub> values of 1.27 M·mL/s·g for 3,3,5,5′-tetramethylbenzidine\n(TMB) and 1.97 M·mL/s·g for hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>), respectively, which are at least one or two orders\nhigher than many other reported carbon–noble metal-based nanozymes.\nOur developed CN-Pt NPs were further utilized in a colorimetric immunoassay\nas signal amplifiers for the biomarker detection of Burkholderia pseudomallei, a Gram-negative bacterial\npathogen classified as a tier 1 select agent by the US CDC. The assay\nachieved lower limits of detection of 0.11 ng/mL in phosphate-buffered\nsaline (PBS) and 0.16 ng/mL in human serum, when compared to many\nother assays in detecting the same biomarker.