Electrically Facilitated Translocations of Proteins through Silicon Nitride Nanopores: Conjoint and Competitive Action of Diffusion, Electrophoresis, and Electroosmosis

Abstract

Solid-state nanopores bear great potential to be used to probe single proteins; however, the passage of proteins through nanopores was found to be complex, and unexpected translocation behavior with respect to the passage direction, rate, and duration was observed. Here we study the translocation of a model protein (avidin) through silicon nitride nanopores focusing on the electrokinetic effects that facilitate protein transport across the pore. The nanopore zeta potential zeta(pore) and the protein zeta potential zeta(protein) are measured independently as a function of solution pH. Our results reveal that electroosmotic transport may enhance or dominate and reverse electrophoretic transport in nanopores. The translocation behavior is rationalized by accounting for the charging states of the protein and the pore, respectively; the resulting translocation direction can be predicted according to the difference in zeta potentials, zeta(protein) - zeta(pore). When electrophoresis and electroosmosis cancel each other out, diffusion becomes an effective (and bias-independent) mechanism which facilitates protein transport across the pore at a significant rate.

Disentangling Steric and Electrostatic Factors in Nanoscale Transport Through Confined Space

“…(iii) Finally, our model does not explicitly consider the effects of electro-osmotic flow (EOF) which has previously been shown to be important in determining DNA translocation kinetics. 50,65,66 However, it is unlikely that EOF plays a major role in our experiments because the average flux of the ions inside the pore blocked by the peptide-DNA conjugate is very low.…”

Probing surface hydrophobicity of individual protein at single-molecule resolution using solid-state nanopores

“…troosmotic (EO) effects were proved to play a vital role in these translocations [48][49][50]. EO effect may enhance or counteract electrophoresis and it is the combined action of electrophoretic (EP) and EO forces that governs the translocation direction of protein across the nanopores [48].…”

“…EO effect may enhance or counteract electrophoresis and it is the combined action of electrophoretic (EP) and EO forces that governs the translocation direction of protein across the nanopores [48]. The protein and wall of SiN nanopore is negatively charged on the whole at pH 9 so the electrophoretic transport is toward the cis side while the EO transport is toward the trans side.…”

Controlling molecular transport through nanopores

“…The surface charge and thus the electroosmotic flow can be tuned by the salt concentration and the pH of the buffer used. Following experiments on protein translocation through solid-state nanopores [78], Rant and co-workers [79] used this idea to facilitate the translocation of proteins through nanopores and could even reverse the translocation direction by adjusting the buffer parameters. This is a direct consequence of the complex interplay between hydrodynamic and electrokinetic forces in nanopores [80].…”