A composite prepared from MnO₂ nanosheets and a deep eutectic solvent as an oxidase mimic for the colorimetric...

A composite was fabricated from deep eutectic solvent and MnO₂ nanosheets (DES/MnO₂) and is shown to be a viable oxidase mimic. The property, morphology and composition of DES/MnO₂ was characterized. DES/MnO₂ displays oxidase-like activity and can oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to form a blue product (oxTMB) with an absorption maximum at 652 nm. Due to the presence of the DES, the polyanionic and negatively charged DNA is easily adsorbed on the surface of the composite by hydrogen bonding and electrostatic interactions. This leads to the inhibition of the oxidase-mimicking activity of DES/MnO₂. This finding was used to design a colorimetric method for the determination of DNA. The assay work in the 10-100 μg mL^-1 DNA concentration range and has a detection limit of 0.37 μg mL^-1. The inhibiting mechanism was further studied by zeta potential measurements, dynamic light scattering and transmission electron microscopy. The selectivity study shows the DES/MnO₂-TMB system to be highly selective for DNA when compared with many proteins, carbohydrates, salts and amino acid. RNA, on the other hand, interferes. The real sample analysis result illustrates that the new method can be used for the detection of DNA in bovine whole blood. Graphical abstractA novel oxidase mimic based on deep eutectic solvent-functionalized MnO₂ nanosheets was synthesized, which can directly catalyze oxidation of 3,3',5,5'-tetramethylbenzidine (TMB, colorless) to oxTMB (blue). A sensitive and convenient colorimetric strategy for visual detection of DNA was established through DES/MnO₂-TMB sensing system.