Reversible pH switchable oxidase-like activities of MnO2 nanosheets for a visual molecular majority logic gate

Abstract

Although the enzyme-like activities of MnO₂ nanosheets have been investigated, effective strategies for modulating their activities are still lacking. Herein, inspired by the pH-dependent activity of natural enzymes, we demonstrate that the oxidase-like activities of the MnO₂ nanosheets are pH switchable and reversible. The MnO₂ nanosheets show oxidase-like activities in an acidic medium, which can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to form blue oxidized TMB (oxTMB), while the corresponding activities are greatly weakened under alkaline conditions. The reaction mechanism is attributed to the fact that the MnO₂ nanosheets can be transformed into hexagonal Na₄MnO₄ with a low reaction activity in an alkaline environment. Using the pH switchable oxidase-like activities of the MnO₂ nanosheets and other reaction processes, we construct a visual three-input molecular majority logic gate with a single-vote veto function. In addition, an OR-INH cascade logic circuit is successfully realized as well.