MnO2 nanosheets based catechol oxidase mimics for robust electrochemical sensor: Synthesis, mechanism and its application for ultrasensitive and selective detection of dopamine

Nanozymes have favorable activity and good stability, which are potential alternatives to natural enzymes and widely applied in biosensing. However, nanozymes based electrochemical sensors are fewer, because many nanozymes are not easy to form efficient electrocatalytic interface and experience interference from the possible oxidizable species. Herein, ultrathin MnO2 nanosheets (MnO2 NSs) were synthesized by reduction of KMnO4 in acidic environment by chemical precipitation method. The MnO2 NSs show excellent catechol oxidase mimicking activity. The steady-state kinetics of MnO2 NSs shows a higher Vmax of 3.441 µM s−1. Additionally, the catalytic mechanism is that in the presence of oxygen, catechol or its analogues are oxidized to quinone or quinoids, while oxygen is reduced to H2O. Afterwards, the possible mechanism of dopamine (DA) at MnO2 NSs-modified electrode is investigated. DA is first catalytically oxidized to dopamine quinone (DQ) by MnO2 NSs based catechol oxidase, which further undergoes irreversible electrochemical reduction to DA involving two protons and two electrons transfer during the process. On the basis of this, a selective and ultrasensitive amperometric detection of DA at 0.0 V (vs. SCE) was explored, which have two linear parts, 0.01–20 μM and 20–100 μM DA with the LOD of 4.1 nM (S/N = 3). Most importantly, the presence of oxidizable species including ascorbic acid, uric acid and cysteine may coexist with DA in biological systems do not exhibit any appreciable interference. The as-proposed method was applicable to detect DA in human serum samples with good satisfactory accuracy and recovery. This research casts prospect to apply nanozymes for electrochemical sensor with excellent analytical performance.