Stabilization and isotachophoresis of unmodified gold nanoparticles in capillary electrophoresis

Capillary zone electrophoresis (CZE) of gold nanoparticles (Au NPs) was investigated in terms of dispersion stability during the analysis process. It was shown that CZE of Au NPs can be performed under dynamic coating conditions depending on the background electrolyte (BGE) composition. The influence of both the co-ion and counter-ion in the BGE was evaluated. It was proven that the application of relatively large buffering counter-ions provides steric stability to NPs during CZE. Among the investigated co-ions, citrate and MOPS were found to be advantageous for the CZE of Au NPs. On the other hand, the presence of zwitterionic substances and multiply charged counter-ions in BGE was shown to promote the aggregation and adsorption of the NPs to the capillary wall. A correlation between the particle stability in CZE and isotachophoresis (ITP) performance was observed and discussed. A sensitivity improvement by two orders of magnitude was achieved using the developed ITP methods.