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-CoN_(3))could serve as highly efficient oxidase mimic.Compared with the typical planar four-coordination structure(SA-CoN_(4)),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 O_(2) molecule and thus improve their oxidase-like activity.Based on the enhanced oxidase-like activity of SA-CoN_(3),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 0.66μM.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.