Ion transport and selectivity in biomimetic nanopores with pH-tunable zwitterionic polyelectrolyte brushes

Zeng, Zhenping; Yeh, Li‐Hsien; Zhang, Mingkan; Qian, Shizhi

doi:10.1039/c5nr05828g

Cited by 81 publications

(79 citation statements)

References 53 publications

(130 reference statements)

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“…The phenomena and mechanisms associated with nanochannels/nanopores rest mainly on the nonuniform distribution of ion species and the overlapping of the electric double layer (EDL) in their interior [11, 12]. The overlapping of EDL influences significantly the transport of ions inside a nanochannel/nanopore, yielding interesting and important phenomena such as ion concentration polarization [13, 14], ion selectivity [15, 16], and ionic current rectification (ICR) [17–19].…”

Section: Introductionmentioning

confidence: 99%

Ion current rectification behavior of a nanochannel having nonuniform cross‐section

2020

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Ion current rectification behavior of a nanochannel having nonuniform cross-sectionDue to its versatile applications in biotechnology, ion current rectification (ICR), which arises from the asymmetric nature of the ion transport in a nanochannel, has drawn much attention, recently. Here, the ICR behavior of a pH-regulated nanochannel comprising two series connected cylindrical nanochannels of different radii is examined theoretically, focusing on the influences of the radii ratio, the length ratio, the bulk concentration, and the solution pH. The results of numerical simulation reveal that the rectification factor exhibits a local maximum with respect to both the radii ratio and the length ratio. The values of the radii ratio and the length ratio at which the local maximum in the rectification factor occur depend upon the level of the bulk salt concentration. The rectification factor also shows a local maximum as the solution pH varies. Among the factors examined, the solution pH influences the ICR behavior of the nanochannel most significantly.Abbreviations: AAO, anodic aluminum oxide; EDL, electric double layer; ICR, ion current rectification; IEP, isoelectric point been concluded that the ICR phenomenon of nanochannels/nanopores can be attributed to their asymmetric characteristics. These include, for instance, geometry [20][21][22][23][24][25][26][27][28], surface charge [29, 30], chemical composition [31, 32], wettability [33], and external applied fields such as pH gradient [34], electrolyte concentration gradient [35], and pressure gradient [36]. Among these, geometry-induced ICR draws much attention because the associated nanochannel fabrication methods are convenient and controllable. These include, for example, track-etching [37], focused ion beam sculpting [38], and electron-beam lithography [39]. Through these methods, various types of nanochannels have been fabricated such as cylindrical [27], conical [22], hourglass-shaped [26], cigar-shaped [20], bullet-shaped [25], dumbbell-shaped [21], and funnelshaped nanochannels [23]. The ICR behavior of an asymmetric nanochannel can be influenced by factors including ionic species [40], ion concentration [35, 41], applied electric potential [40], pH [42, 43], temperature [44], and nanochannel length and its opening radii [24,45,46]. The cone angle [24] and the ratio of cylindrical segment/conical segment [23] are important to conical and funnel-shaped nanochannels, respectively.Previous studies regarding asymmetric nanochannel focused mainly on polymeric material such as polycarbonate Color online: See article online to view Figs. 1-8 in color.

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Section: Introductionmentioning

confidence: 99%

Ion current rectification behavior of a nanochannel having nonuniform cross‐section

2020

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“…The second important issue probed in this study is the use of this mean‐field thermodynamics and electrostatics model in quantifying an external electric field driven ionic current. While ionic current has been previously studied in PE‐brush‐grafted nanochannels theoretically , this is for the first time a theoretical model on ionic current, appropriately accounting for the PE configuration and thermodynamics, has been developed. The key result is a most remarkable enhancement of ionic current for smaller pH, despite a smaller magnitude of EDL potential at such pH values.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamics, electrostatics, and ionic current in nanochannels grafted with pH‐responsive end‐charged polyelectrolyte brushes

Chen

Das

2017

Electrophoresis

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In this paper, we study the thermodynamics, electrostatics, and an external electric field driven ionic current in a pH-responsive, end-charged polyelectrolyte (PE) brush grafted nanochannel. By employing a mean field theory, we unravel a highly nonintuitive interplay of pH and electrolyte salt concentration in dictating the height of the end-charged PE brush. Larger pH or weak hydrogen ion concentration leads to maximum ionization of the charge-producing group-as a consequence, the resulting the electric double layer (EDL) energy get maximized causing a maximum deviation of the brush height from the value (d ) of the uncharged brush. This deviation may result in enhancement or lowering of the brush height as compared to d depending on whether the PE end locates lower or higher than h/2 (h is the nanochannel half height) and the salt concentration. Subsequently, we use this combined PE-brush-configuration-EDL-electrostatics framework to compute the ionic current in the nanochannel. We witness that the ionic current for smaller pH is much larger despite the corresponding magnitude of the EDL electrostatic potential being much smaller-this stems from the presence of a much larger concentration of H+ ions at small pH and the fact that H+ ions have very large mobilities. In fact, this ionic current shows a steep variation with pH that can be useful in exploring new designs for applications involving quantification and characterization of ionic current in PE-brush-grafted nanochannels.

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“…3–5 Such stimuli-responsive brushes have found numerous applications, including biosensors, 6 separation technologies, 7 and as valves for nanopores. 8 Two important and historically persistent limitations of synthetic polymers are the challenge of precisely controlling chain length and monomeric sequence, both of which strongly influence electrostatic properties. Most polyelectrolytes so far synthesized have therefore either been homopolymers consisting of a single type of charged group, 9,10 random copolymers formed of a combination of two or more chemical species (at least one of which is charged) randomly distributed over the polymer length, 10,11 or block copolymers composed of repeats of discrete charged blocks.…”

Section: Introductionmentioning

confidence: 99%

Site-Specific Modulation of Charge Controls the Structure and Stimulus Responsiveness of Intrinsically Disordered Peptide Brushes

et al. 2016

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Intrinsically disordered proteins (IDPs) are an important and emerging class of materials for tailoring biointerfaces. While the importance of chain charge and resultant electrostatic interactions in controlling conformational properties of IDPs is beginning to be explored through in silico approaches, there is a dearth of experimental studies motivated toward a systematic study of these effects. In an effort to explore this relationship, we measured the conformations of two peptides derived from the intrinsically disordered neurofilament (NF) side arm domain: one depicting the wild-type sequence with four lysine–serine–proline repeats (KSP peptide) and another in which the serine residues were replaced with aspartates (KDP peptide), a strategy sometimes used to mimic phosphorylation. Using a variety of biophysical measurements including a novel application of scanning angle interference microscopy, we demonstrate that the KDP peptide assumes comparatively more expanded conformations in solution and forms significantly thicker brushes when immobilized on planar surfaces at high densities. In both settings, the peptides respond to changes in ambient ionic strength, with each peptide showing distinct stimulus-responsive characteristics. While the KDP peptide undergoes compaction with increasing ionic strength as would be expected for a polyampholyte, the KSP peptide shows biphasic behavior, with an initial compaction followed by an expanded state at a higher ionic strength. Together these results support the notion that modulation of charge on IDPs can regulate conformational and interfacial properties.

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Ion transport and selectivity in biomimetic nanopores with pH-tunable zwitterionic polyelectrolyte brushes

Cited by 81 publications

References 53 publications

Ion current rectification behavior of a nanochannel having nonuniform cross‐section

Ion current rectification behavior of a nanochannel having nonuniform cross‐section

Thermodynamics, electrostatics, and ionic current in nanochannels grafted with pH‐responsive end‐charged polyelectrolyte brushes

Site-Specific Modulation of Charge Controls the Structure and Stimulus Responsiveness of Intrinsically Disordered Peptide Brushes

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