A sensitive colorimetric assay for cholesterol based on the peroxidase-like activity of MoS.sub.2 nanosheets

The authors describe a colorimetric method for the determination of cholesterol in human serum. Cholesterol is enzymatically oxidized by oxygen in the presence of cholesterol oxidase (ChOx) to produce 4-cholestene-3-one and hydrogen peroxide (H.sub.2O.sub.2). Due to the peroxidase-like activity of MoS.sub.2 nanosheets, H.sub.2O.sub.2 can oxidize the chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) to give a blue product. The increase in the absorbance of the acidic oxTMB solution at 450 nm is used for quantification of cholesterol. Under the optimal conditions, the increase in absorbance is proportional to the concentration of cholesterol in the range from 2 to 200 [mu]mol·L.sup.-1, and the limit of detection is 0.76 [mu]mol·L.sup.-1. The color change from pale yellow to blue color can also be detected visually for cholesterol concentrations as low as 20 [mu]mol·L.sup.-1. Such an enzyme mimetic-based assay possesses advantages over enzyme-based assays in terms of costs, stability against denaturation, and protease digestion. The assay was applied to the determination of free cholesterol and of total cholesterol (after hydrolysis using an esterase) in spiked human serum, and it gave satisfactory recoveries.