Adding sodium dodecylsulfate to the running electrolyte enhances the separation of gold nanoparticles by capillary electrophoresis

Abstract This paper describes employing capillary electrophoresis (CE) for the separation of gold colloids in nanometer-size regimes. Adding sodium dodecylsulfate (SDS) surfactant to the running buffer enhances the capability of CE to separate gold nanoparticles. We found that the optimized separation conditions involved SDS (70 mM), 3-cyclohexylamoniuopropanesulfonic acid (CAPS) buffer (10 mM), pH 10.0, and an applied voltage of 20 kV. We propose that the charged surfactants associate onto the surface of the gold nanoparticles and cause a change in the charge-to-size ratio of gold nanoparticle, which is a function of the surface area of nanoparticle and the surfactant concentration of running electrolyte. At high concentrations of the surfactant in the running electrolyte—i.e., when the surface of the gold nanoparticles is fully occupied with SDS—a linear relationship exists between the electrophoretic mobility and nanoparticles having diameters ranging from 5.3 to 38 nm. Based on the results of separating the 5.3 and 19 nm nanoparticles, we estimate that the size resolution ( R s =1.0) is 5.0 nm. The relative standard deviations of the electrophoretic mobilities of the 5.3 and 19 nm gold nanoparticles are 0.97 and 0.54%, respectively.