Importance of Polyelectrolyte Modification for Rectifying the Ionic Current in Conically Shaped Nanochannels

doi:10.1039/c6cp07693a

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Title:	Importance of Polyelectrolyte Modification for Rectifying the Ionic Current in Conically Shaped Nanochannels
Authors:	Hsu, J.P., Wu, H.H., C.Y. Lin, and S. Tseng
Date:	2017-02
Issue Date:	2018-04-14 12:10:36 (UTC+8)
Abstract:	Due to its capability of mimicking ion channels in living organisms, the ionic transport in artificial nanochannels/nanopores has drawn the attention of researchers in various fields.1–3 Recent advances in nanochannel/nanopore fabrication technology also make relevant applications versatile. These include, for example, sensing of biomolecules and ions,4–12 ionic gates,13–15 energy conversion,16–18 and water desalination.19 Fu et al.4 showed that nanopipettes can be used in DNA sequencing through monitoring the ionic current shift. Ali et al.5 studied the binding capability of calcium ions by a conical nanopore coated with poly acid chains. Umehara et al.6 proposed the use of various materials and methods for nanopipettes based biosensing. German et al.8 and Lan et al.9 investigated the translocation of nanoparticles in a glass nanopore. Vogel et al.10 estimated the size of a nanoparticle by its translocation in a polymeric conical nanopore. As the size of a nanochannel is down to the order of the Debye length (or the thickness of an electric double layer, EDL), the overlapping of EDLs yields distinctive electrokinetic phenomena including, for example, ion concentration polarization (ICP),20,21 ion selectivity,22,23 and ionic current rectification (ICR).24–27 ICR is the phenomenon that a nanochannel/ nanopore shows a diode-like current–voltage behavior, or the preference for ionic current in a certain direction when an electric potential bias is applied. In biological science, ICR is observed in ion channels such as those of K+ and Na+.28–30 For charged nanochannels, ICR might arise from, for instance, asymmetric pore geometry,26,31–34 the imposed salt gradient,22,35–37 and bipolar surface properties.38–41 Polyelectrolyte (PE) is often used to modify the surface of inorganic13,36,42,43 and organic nanochannels,14,44,45 providing them a versatile characteristic and, therefore, an ICR nature.44,46 Zhang et al.,13 for example, found that a glass conical nanopore modified by poly[2-(dimethylamino)ethyl methacrylate], a smart homopolymer capable of undergoing conformational transitions stimulated by pH and temperature, exhibits ICR behavior. Umehara et al.42 showed that after coating with poly-L-lysine a quartz nanopipette is capable of amplifying ionic current and giving a rectification direction opposite to that of an uncoated nanopipette. In a study of the ICR of a glass nanopipette coated with PEI, Deng et al.36 found that its rectification factor has a local maximum as the bulk salt concentration varies, regardless of whether a salt gradient is applied. The coating of materials on a nanopore also provides a way for estimating the pKa of the coating materials through the experimentally measured pH–ionic current relationship. Liu et al.,43 for instance, estimated the pKa of polyethyleneimines (PEIs) by coating them on a glass nanopipette.
Relation:	Physical Chemistry Chemical Physics 19, 5351-5360
DOI:	10.1039/c6cp07693a
Appears in Collections:	[Graduate Institute & Department of Mathematics] Journal Article

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