Investigating protein translocation in the presence of an electrolyte concentration gradient across a solid-state nanopore.

Electrolyte chemistry plays an important role in the transport properties of analytes through nanopores. Here, we report the translocation properties of the protein human serum transferrin (hSTf) in asymmetric LiCl salt concentrations with either positive (Ctrans /Ccis < 1) or negative chemical gradients (Ctrans /Ccis > 1). The cis side concentration was fixed at 4 M for positive chemical gradients and at 0.5 M LiCl for negative chemical gradients, while the trans side concentration varied between 0.5 to 4 M which resulted in six different configurations, respectively, for both positive and negative gradient types. For positive chemical gradient conditions, translocations were observed in all six configurations for at least one voltage polarity whereas with negative gradient conditions, dead concentrations where no events at either polarity were observed. The flux of Li+ and Cl- ions and their resultant cation or anion enrichment zones, as well as the interplay of electrophoretic and electroosmotic transport directions, would determine whether hSTf can traverse across the pore.