Charge-Selective Transport of Protein Molecules through Solid-State Nanochannels

In recent years, molecular transport through solid-state nanochannels mimicking selective transport properties of biological ion channels has attracted considerable attention. In both synthetic and biological channels, these properties strongly depend on size and surface charge. Especially, heavy ion track-etched nanochannels are widely used for selective transport and separation of molecules, including biomolecules. Up to now, surface charge manipulation of nanochannels, fabricated in polymer membranes, is mostly achieved by electroless gold plating and subsequent chemisorption of thiomolecules having variable charge polarity [1]. In this report, we describe a facile and straightforward approach for the manipulation of surface charge of nanochannels in polyethyleneterephthalate (PET) membranes via carbodiimide chemistry (Figure 1) [2]. At about neutral pH, carboxyl (-COO) groups which were generated during the track-etching process, import negative charge to the channel surface. After functionalization of these groups with ethylendiamine, the channel surface was positively charged due to protonation of terminal amino (NH3) groups. For the selective transport of charged biomolecules, the membranes with areal density of ~ 3 x 10 channels/cm were used. The diameter (75 ± 4 nm) of cylindrical nanochannels was confirmed through FESEM images of gold nanowires deposited in these nanochannels. Charged protein molecules such as lysozyme and bovine serum albumin (BSA) were selected for masstransport experiments. Briefly, the membrane was mounted between the two halves of a conductivity cell. The feed half-cell contains 10 M of a biomolecule in electrolyte solution, the permeate half-cell contains pure electrolyte solution. Both solutions were continuously stirred during the whole process. After a preset time, the biomolecule concentration in the permeate half-cell was determined by measuring the UV absorbance.