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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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