Mass Transfer and Flow in Electrically Charged Micro- and Nanochannels

Conlisk, A. T.; McFerran, Jennifer; Zheng, Zhi; Hansford, Derek J.

doi:10.1021/ac011198o

Cited by 124 publications

(96 citation statements)

References 17 publications

(23 reference statements)

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“…When the diameter of the pore is small compared to the EDL, the situation is theoretically more complex. In this case, v eo varies across the diameter of the tube, never reaching the value obtained in a wide tube, and as a consequence the overall flow rate is greatly reduced (15). Difficulties in estimating have led to approaches that relate the measured current rather than the applied potential to solvent flow.…”

Section: Discussionmentioning

confidence: 99%

“…For example, electroosmosis has been used to produce solvent flow through channels in microfluidic systems, which range from a few to several hundred micrometers in diameter (11)(12)(13). In these systems, the electrical double layer (EDL) is small compared to the diameter of the channel, generating convective plug flow (14,15) that includes dissolved neutral molecules. Despite its apparent simplicity, the theoretical basis of electroosmotic flow in relatively wide channels remains under active discussion and experimental evaluation (16)(17)(18)(19).…”

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Electroosmotic enhancement of the binding of a neutral molecule to a transmembrane pore

Cheley

Bayley

2003

Proc. Natl. Acad. Sci. U.S.A.

131

151

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The flux of solvent water coupled to the transit of ions through protein pores is considerable. The effect of this electroosmotic solvent flow on the binding of a neutral molecule [␤-cyclodextrin (␤CD)] to sites within the staphylococcal ␣-hemolysin pore was investigated. Mutant ␣-hemolysin pores were used to which ␤CD can bind from either entrance and through which the direction of water flow can be controlled by choosing the charge selectivity of the pore and the polarity of the applied potential. The K d values for ␤CD for individual mutant pores varied by >100-fold with the applied potential over a range of ؊120 to ؉120 mV. In all cases, the signs of the changes in binding free energy and the influence of potential on the association and dissociation rate constants for ␤CD were consistent with an electroosmotic effect. W e have been interested in the interaction of the staphylococcal ␣-hemolysin (␣HL) pore with ␤-cyclodextrin (␤CD) and other small, rigid host molecules, because they can act as molecular adapters after becoming lodged in the lumen of the pore. There, they alter conductance (1, 2) and ion selectivity (3) and act as sites where blockers can bind (1). The latter allows ␣HL⅐␤CD complexes to act as components of stochastic sensors for organic analytes (1, 4). In a recent study, we suggested that the interaction of the neutral ␤CD molecule with the ␣HL pore could be strengthened or weakened by electrokinetically driven water flow (5). Here, we test this idea thoroughly by using mutant ␣HL pores to which ␤CD can bind from either entrance.The WT ␣HL pore is a heptamer of known structure (6) with a unitary conductance of 650 pS at Ϫ40 mV in 1 M NaCl at pH 7.5 (7). If the pore were completely charge-selective (it is not; see Results), the current at Ϫ40 mV would translate into a unidirectional movement of 1.6 ϫ 10 . Therefore, even where charge selectivity is modest (for the WT ␣HL pore P Naϩ ͞P ClϪ ϭ 0.78, pH 7.5), the water flux is well above 10 8 molecules s Ϫ1. Here, we show that this flux, i.e., electroosmotic flow, can provide a driving force that significantly alters the binding strength of the neutral ␤CD molecule within the lumen of the ␣HL pore.Electroosmotic flow has been examined previously for channels with a wide range of dimensions. For example, electroosmosis has been used to produce solvent flow through channels in microfluidic systems, which range from a few to several hundred micrometers in diameter (11-13). In these systems, the electrical double layer (EDL) is small compared to the diameter of the channel, generating convective plug flow (14, 15) that includes dissolved neutral molecules. Despite its apparent simplicity, the theoretical basis of electroosmotic flow in relatively wide channels remains under active discussion and experimental evaluation (16)(17)(18)(19). Individual polymer-filled cation-selective pores of Ϸ100-m diameter have been studied by White and colleagues (20, 21). They used a scanning electrochemical microscope tip to measure the rate of transport of neutral ...

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Electroosmotic enhancement of the binding of a neutral molecule to a transmembrane pore

Cheley

Bayley

2003

Proc. Natl. Acad. Sci. U.S.A.

131

151

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“…͑52͒ are compared in Fig. 14͑a͒ for different ionic strengths ͑Qu and Conlisk et al, 2002;Conlisk, 2005͒. It is known that the DebyeHückel approximation generally overestimates the electric potential.…”

Section: Model Of the Exclusion-enrichment Effectmentioning

confidence: 99%

Transport phenomena in nanofluidics

2008

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The transport of fluid in and around nanometer-sized objects with at least one characteristic dimension below 100 nm enables the occurrence of phenomena that are impossible at bigger length scales. This research field was only recently termed nanofluidics, but it has deep roots in science and technology. Nanofluidics has experienced considerable growth in recent years, as is confirmed by significant scientific and practical achievements. This review focuses on the physical properties and operational mechanisms of the most common structures, such as nanometer-sized openings and nanowires in solution on a chip. Since the surface-to-volume ratio increases with miniaturization, this ratio is high in nanochannels, resulting in surface-charge-governed transport, which allows ion separation and is described by a comprehensive electrokinetic theory. The charge selectivity is most pronounced if the Debye screening length is comparable to the smallest dimension of the nanochannel cross section, leading to a predominantly counterion containing nanometer-sized aperture. These unique properties contribute to the charge-based partitioning of biomolecules at the microchannel-nanochannel interface. Additionally, at this free-energy barrier, size-based partitioning can be achieved when biomolecules and nanoconstrictions have similar dimensions. Furthermore, nanopores and nanowires are rooted in interesting physical concepts, and since these structures demonstrate sensitive, label-free, and real-time electrical detection of biomolecules, the technologies hold great promise for the life sciences. The purpose of this review is to describe physical mechanisms on the nanometer scale where new phenomena occur, in order to exploit these unique properties and realize integrated sample preparation and analysis systems.

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“…Karlsson et al [10] have presented fluidic control in lipid nanotubes 50-150 nm in radius, conjugated with surface immobilized unilamellar lipid bilayer vesicles (5-25 mm in diameter). Conlisk et al [11] have examined the fluid flow and mass transfer under an electric field in a rectangular microchannel and nanochannel. In fact, as early as middle 1960s, Burgreen et al [12] had already reported a similar study of electrokinetic flow (EKF) in very fine capillary channels of rectangular cross section, just like those channels in chips nowadays, which was a natural extension of the general theory of EKF.…”

Section: Introductionmentioning

confidence: 99%