Protein Transport in Nanoporous Membranes Modified with Self-Assembled Monolayers of Functionalized Thiols

Abstract

Control of external pH and ionic strength is used to separate proteins with surface-modified, nanoporous polycarbonate track etched (PCTE) membranes. The porous PCTE membranes were modified with monolayers of self-assembled thiols (HSC10H20COOH) on electroless gold. The hydraulic radius of the pores in the surface-modified membranes was 8.7 nm. Two proteins of nearly identical molecular weight, bovine serum albumin (BSA) and bovine hemoglobin (BHb), were used as the permeants. The fluxes of BSA and BHb through the membranes show maximum values at the isoelectric points (pI) of the proteins. At pH values above and below the pI, charge interactions between the proteins, their counterions, and the pore surface leads to a decrease in flux. The imposition of a difference in ionic strength across the membrane causes osmotic flow and leads to a significant increase in the protein fluxes and an enhancement of the selectivity of BSA over BHb. In protein separation experiments, the BSA and BHb fluxes are nearly 3 times larger than those observed with no ionic strength difference.

Electrochemical detection of hydrogen peroxide on platinum-containing tetrahedral amorphous carbon sensors and evaluation of their biofouling properties

“…Samples were also immersed in deionized water for reference. The isoelectric point of BSA is 4.7 [50] and that of ta-C is 2.6 [24] which indicates that the surface should in general repel the protein both in neutral pH as well as below pH 1. However, it should also be noted that protein absorption is a complex process and cannot be predicted based on a single parameter such as charging.…”

Transport phenomena in nanofluidics

“…The curve illustrates three zones: for pH Յ 7 and pH Ն 9, the diffusion of lectin through the nanochannel is slow, whereas the diffusion is significantly faster for pH values between 7 and 9. Three peaks are visible in this part of the curve, one at pH = 7.5, a second at pH = 8.2, and a third at pH = 8.8, and they can be attributed to the pI values of the three proteins, showing a maximal diffusion coefficient through the nanochannel if they are neutral and do not have electrostatic interactions with channel walls ͑Burns and Zydney, 1999; Chun and Stroeve, 2002;Ku and Stroeve, 2004͒. For pH Ն 9, all three proteins are negatively charged and excluded from the nanochannel according to the EEE ͓Eq.…”

Protein diffusion through charged nanopores with different radii at low ionic strength

“…We have shown previously for the case of narrow pores that, by adjusting the solution pH to the pI of one of the proteins, the transport of the other is hindered by the electrostatic interaction between the protein and the surface pore charges. 5 Protein flux reaches a maximum at pI while the electrostatic interaction decreases this flux at higher or lower pH values. 5 In addition to the pH, the ionic strength of the solution can also modify the electrostatic interaction between the protein and the pore as well as the protein conformation.…”

“…5 Protein flux reaches a maximum at pI while the electrostatic interaction decreases this flux at higher or lower pH values. 5 In addition to the pH, the ionic strength of the solution can also modify the electrostatic interaction between the protein and the pore as well as the protein conformation. Note that the ionic strength dictates the Debye screening length in the solution.…”

“…Protein diffusion through nanoporous membranes is affected by a multitude of parameters such as osmotic pressure, 1 electric field, 2 membrane thickness, 3 protein size (molecular weight), pore diameter, protein electrostatic charge and concentration, 4 charge distribution and shape of the protein, pore shape and functional groups on the pore surface, ionic strength, 5 pH, and temperature. In principle, the combination of these parameters may provide tools to control the transport of the protein.…”