Probing NAD+/NADH-dependent biocatalytic transformations based on oxidase mimics of MnO2

Abstract In the present study, a novel colorimetric sensing platform was constructed for probing the NAD+/NADH-dependent biocatalytic transformations. Manganese dioxide (MnO2) nanosheets as an oxidase-mimicking nanomaterial could directly oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) into oxTMB without the need of H2O2. Importantly, it was found that NADH could easily trigger the decomposition of MnO2 nanosheets, causing the decrease of solution absorbance. This is demonstrated by the enzyme catalysis reactions of two dehydrogenase models, ethanol dehydrogenase (ADH) and lactate dehydrogenase (LDH), where NADH is formed and consumed, respectively, in their physiological enzymatic reactions. A MnO2-TMB sensing platform was thereby proposed for the analysis of their catalytic reaction substrates including ethanol and pyruvic acid. The detection limits of ethanol and pyruvic acid can reach 5.0 μM and 100 nM, respectively. The developed optical biosensing platform can be used to develop other dehydrogenase-based biosensors followed by monitoring their substrates.