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-xP₁, 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-xP₁ nanozymes with different Co-P dual-site distances and show that CoN₃P₁ 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 CoN₃P₁ 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.