Modulation of electrophoresis, electroosmosis and diffusion for electrical transport of proteins through a solid-state nanopore.

Nanopore probing of molecular level transport of proteins is strongly influenced by electrolyte type, concentration, and solution pH. As a result, electrolyte chemistry and applied voltage are critical for protein transport and impact, for example, capture rate ( ), transport mechanism (, electrophoresis, electroosmosis or diffusion), and 3D conformation (, chaotropic kosmotropic effects). In this study, we explored these using 0.5-4 M LiCl and KCl electrolytes with holo-human serum transferrin (hSTf) protein as the model protein in both low (±50 mV) and high (±400 mV) electric field regimes. Unlike in KCl, where events were purely electrophoretic, the transport in LiCl transitioned from electrophoretic to electroosmotic with decreasing salt concentration while intermediate concentrations (, 2 M and 2.5 M) were influenced by diffusion. Segregating diffusion-limited capture rate ( ) into electrophoretic ( ) and electroosmotic ( ) components provided an approach to calculate the zeta-potential of hSTf ( ) with the aid of and zeta potential of the nanopore surface ( ) with ( - ) governing the transport mechanism. Scrutinization of the conventional excluded volume model revealed its shortcomings in capturing surface contributions and a new model was then developed to fit the translocation characteristics of proteins.