A colorimetric heparin assay based on the inhibition of the oxidase mimicking activity of cerium oxide nanoparticles

A colorimetric method is described for the sensitive detection of heparin (Hep). It is based on the finding that Hep can effectively inhibit the oxidase mimicking activity of cerium oxide nanoparticles (nanoceria). In the presence of Hep, the catalytic activity of nanoceria toward the oxidation of the chromogenic substrate 3,3', 5,5'-tetramethylbenzidine by oxygen is strongly decreased. The inhibition mechanism is attributed to the fact that Hep is adsorbed on the surface of the nanoceria. Under optimal condition, the absorbance (measured at 652 nm) decreases with increasing Hep concentrations in the range from 30 to 700 nM. The detection limit is 20 nM. The method was applied to the determination of Hep in medical injection sample and serum sample with satisfactory results.