Extremely highly efficient on-line concentration and separation of gold nanoparticles using the reversed electrode polarity stacking mode and surfactant-modified capillary electrophoresis

Abstract

In this study, gold nanoparticles (Au NPs) were separated using the reversed electrode polarity stacking mode (REPSM) of a capillary electrophoresis (CE) system for on-line enhancement prior to performing surfactant-modified CE separation. Under optimized conditions [running electrolyte buffer, sodium dodecyl sulfate (70 mM) and 3-cyclohexylamino-1-propanesulfonic acid (10 mM) at pH 10.0; applied voltage, 20 kV; operating temperature, 25 °C; REPSM strategy for sample on-line concentration; REPSM applied prior to initializing separation], two parameters were varied to further enhance the concentration and separation of the Au NPs: (i) the rate of polarity switching (from −20 to +20 kV) between the REPSM and surfactant-modified CE separation modes and (ii) the length of the capillary column. At a polarity switching rate of 1333 kV min −1 and a column length of ca. 83.5 cm, the resolution of the separation of a mixture of 5.3- and 40.1-nm Au NPs was greater than 19; in addition, the numbers of theoretical plates for the 5.3- and 40.1-nm-diameter Au NPs were greater than 15,000 and up to 1.15 × 10 7, respectively—the latter being extremely high. Thus, this CE-based method for separating Au NPs provided high performance in terms of separation resolution and the number of theoretical plates, both of which were improved by greater than fivefold relative to those published previously. Notably, the sensitivity enhancement factors for the 5.3- and 40.1-nm-diameter Au NPs were improved (by ca. 20- and 500-fold, respectively) relative to those obtained using conventional surfactant-modified CE separation.