Dual FeCo single-atom nanozymes with specific oxidase-like activity for sensitive detection of aflatoxin B₁

Single-atom nanozymes (SAzymes) with well-defined metal-nitrogen-carbon coordination structures are of great interest for the development of colorimetric biosensing. However, their catalytic efficiency and specificity is restricted due to the limited number of single metal atoms that can serve as catalytic centre. Therefore, the construction of SAzymes with high activity and specificity is vital but remains challenging. To address these issues, we prepared a bimetallic SAzymes with an independent iron and cobalt structure (FeCo/NC), and the oxidase-like activity was enhanced by >112.8% relative to Fe/NC. This preparation strategy increased the amount of single metal atoms loaded, resulting in a strong synergistic effect and proximity-orientation effects due to the unique structure of single Co and Fe atoms coexisting on graphene. The oxidase-mimicking activity of FeCo/NC was specifically enhanced by co doping, although the activities of peroxidase-, superoxide dismutase-, or catalase-like were not significantly affected. In light of these discoveries, as a symbol of the proof-of-concept, FeCo/NC-based colorimetric immunoassays were developed for sensitive detection of aflatoxin B₁ (AFB₁), achieving a linear range of 0.01-10 ng/mL and a detection limit of 0.005 ng/mL. This study provides a convenient strategy for promoting the catalytic activity and specificity of SAzymes, thereby enhancing their potential in biosensing.