Coordinatively unsaturated cobalt single-atom nanozymes for visual pesticides detection by smartphone-based platform

By adjusting the coordination environment of single-atom catalysts, the enzyme-like activity can be finely tuned for highly sensitive biosensing. Herein, we demonstrated that coordinatively unsaturated cobalt-nitrogen sites doped within porous carbon (SA-CoN3) could serve as highly efficient oxidase mimic. Compared with the typical planar four-coordination structure (SA-CoN4), the as-obtained single-atom Co nanozymes anchored by three nitrogen atoms are found to display much higher oxidase-like catalytic efficiency. Combined theoretical and experimental analysis revealed that the coordinatively unsaturated Co sites could facilitate adsorption and activation of O2 molecule and thus improve their oxidase-like activity. Based on the enhanced oxidase-like activity of SA-CoN3, a paper/smartphone sensor for organophosphorus pesticides (OPs) was successfully constructed and used to quantify glyphosate in environmental and food samples with a low detection limit of 0.66 µM. This work not only highlights the important role of coordination unsaturation of SA nanozymes for promoting oxidase-like activity, but also provides an easy and cost-effective way to conduct effective quantification of OPs in the field.