Gold Nanoparticle Extraction Followed by Capillary Electrophoresis to Determine the Total, Free, and Protein-Bound Aminothiols in Plasma

This study describes the use of Tween 20-capped gold nanoparticles (Tween 20-AuNPs) for the selective extraction and enrichment of five aminothiols, including glutathione, gamma-glutamylcysteine, cysteine, homocysteine, and cysteineglycine, prior to analysis by capillary electrophoresis with UV detection. Tween 20-AuNPs are capable of extracting aminothiols from a complicated matrix because a Tween 20 capping layer can inhibit effectively the nonspecific adsorption. Moreover, Tween 20-AuNPs had better aminothiol loading compared to Zonyl FSN-100- and Triton X-100-capped AuNPs. The extraction efficiency of aminothiols was highly dependent on the number of Tween 20-AuNPs, the concentration of dithiothreitol, and the type of surfactant (i.e., capping agent). Under optimal extraction conditions, the limits of detection at a signal-to-noise ratio of 3 for five aminothiols were down to 10-65 nM. Total and free aminothiols in plasma were determined by varying the order of disulfide reduction with tris(2-carboxyethyl)phosphine. Efficient separation of total and free aminothiols with baseline resolution was successfully achieved by the addition of cationic polyelectrolyte, poly(diallyldimethylammonium chloride), to the background electrolyte. Because this extraction method provided no matrix effect, the concentrations of total and free aminothiols in plasma can be quantified with an external calibration method. On the basis of the advantages of simplicity, high selectivity, high sensitivity, and good reproducibility, this proposed method may have great potential for disease diagnosis.