Quick colorimetric determination of choline in milk and serum based on the use of MoS2 nanosheets as a highly active enzyme mimetic

The authors have synthesized molybdenum disulfide nanosheets (MoS2 nanosheets) by using a bottom-up hydrothermal method. The nanosheets display strong catalytic (enzyme mimetic) activity in catalyzing the oxidation of peroxidase substrate of 3,3',5,5'-tetramethylbenzidine (TMB) in presence of H2O2 to produce a blue product. The peroxidase mimicking properties of MoS2 nanosheets depend on temperature, H2O2 concentration and pH value. A choline assay was worked out where choline was oxidized by choline oxidase in presence of oxygen to produce H2O2 which is colorimetrically detected, best at 652 nm. The method works in the 1 to 180 mu M choline concentration range with a 0.4 mu M detection limit. Color changes may also be detected visually. The assay is simple, highly sensitive, selective and rapid. It was applied in the determination of choline in (spiked) milk and serum.