Unraveling the Proximity Effects of a Co–P Dual Site in Phosphorus-Coordinated Cobalt Single-Atom Nanozymes

Heteroatom coordination in single-atom nanozymes is considered a promising strategy to promote their enzyme-like performance, but the proximity effect of active metal sites and heteroatoms on their catalytic efficiency is still elusive. Herein, we demonstrate that the enzyme-like performance of phosphorus-coordinated cobalt single-atom nanozymes (CoN 4– x P 1, x = 0,1) exhibits a strong dependence on the atomic distance between the Co site and the coordinated P atom (Co–P dual site), where the activity continuously improves with decreasing Co–P distance. Theoretical calculations reveal the proximity effect of the Co–P dual site in optimizing the oxygen adsorption/desorption energy and rate-determining step barrier. Guided by this principle, we synthesize a series of CoN 4– x P 1 nanozymes with different Co–P dual-site distances and show that CoN 3 P 1 nanozymes with direct Co–P coordination exhibit superior catalytic efficiency. In-situ electron paramagnetic resonance spectroscopic (EPR) studies unveil that the phosphorus coordination could switch oxygen activation from a nonradical to hybrid radical/nonradical pathway, enabling efficient reactive oxygen species generation. As a potential application, the optimal CoN 3 P 1 nanozymes with superior oxidase-like activity are successfully applied to the colorimetric-photothermal dual-mode enzyme-linked immunosorbent assay of neuron-specific enolase. The present study highlights the importance of the proximity effect in heteroatom-coordinated single-atom nanozymes and provides insights into the strategic engineering for high-performance nanozymes.