Constructing a novel strategy for one-step colorimetric glucose biosensing based on Co-Nx sites on porous carbon as oxidase mimetics

Nanozyme-based sensing strategy for glucose generally involves a two-step H2O2-bridged cascade reaction. However, this two-step cascade reaction always shows a limited detection efficiency for glucose, which hardly makes simply operation, rapid detection, and sensitivity all promised. Herein, a novel strategy for one-step glucose detection was proposed based on the efficiently competitive relationship between glucose oxidase catalyzed glucose oxidation and oxidase nanozyme catalyzed 3,3′,5,5′-tetramethylbenzidine (TMB) colorimetric oxidation. As a proof of concept, Co-Nx sites on porous carbon (Co-Nx/PC) derived from ZIF-67 was selected as the oxidase nanozyme with O2-sensitive nature, which can activate O2 to produce 1O2 for TMB colorimetric oxidation. In the presence of glucose, the competitive reaction of glucose oxidase catalyzed glucose oxidation occurs, which will obviously inhibit the Co-Nx/PC catalyzed TMB colorimetric oxidation to construct method for glucose detection. The usage of the same reactant O2 and the production of suppressive H2O2 cause a dual effect to this inhibition. In addition, the available pH range of Co-Nx/PC overlaps with that of glucose oxidase, promising a one pot reaction. The proposed method with Co-Nx/PC as oxidase nanozyme based on one-step competitive strategy for glucose detection possesses high detection efficiency with convenience (one-pot), rapidness (total reaction time of 10 min) and sensitivity (LOD of 0.31 μM) all promised, which is superior among the methods based on two-step one-pot or two-pot cascade strategy. The strategy can be successfully applied into the blood glucose detection in human serums with satisfactory results. Also, the strategy can be scalable to other oxidase nanozyme like Mn3O4.