green synthesis of the nanocomposites of MnO/graphene as an oxidase mimic for sensitive colorimetric and electrochemical dual-mode biosensing.

Herein we report the colorimetry and an electrochemical for the determination of dopamine (DA) by using MnO nanoparticles and graphene nanosheets composite (MnO@G) that display oxidase mimicking property. MnO@G could directly oxidize colorless 3,3',5,5'-tetramethylbenzidine (TMB) into a blue product (oxTMB) without extra oxidants such as HO. Nevertheless, the presence of DA will inhibit the TMB oxidation due to the presence of the competitive reaction of MnO@G and DA, giving a product color change from blue to colorless. A colorimetric assay for detect the concentration of DA was worked out according to this finding. Response is linear in the 0.1 to 15 μM DA concentration range, and the detection limit is 0.14 μM. Wider detection range is achieved in an electrochemical method which is due to the pronounced electrocatalytic activity of MnO@G. The MnO@G was modified on the surface of the glassy carbon electrode in order to fabricate one type electrochemical sensor. The sensor achieves a wide detection two linear ranges from 0.4 to 70 μM, with the detection limit of 1.16 μM. The detection of DA in real serum sample proved that the nanozyme based on MnO@G could be developed into a colorimetry and electrochemical dual-readout sensing platform.