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Stationary Chemical Gradients for Concentration Gradient-BasedSeparation and Focusing in Nanofluidic Channels.

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Title:	Stationary Chemical Gradients for Concentration Gradient-BasedSeparation and Focusing in Nanofluidic Channels.
Authors:	Hsu, Wei-Lun¹, Inglis, David W.¹, Jeong, Helen¹, Dunstan, David E.¹, Davidson, Malcolm R.¹, Goldys, Ewa M.¹, Harvie, Dalton J. E.¹
Source:	Langmuir. May2014, Vol. 30 Issue 18, p5337-5348. 12p.
Subjects:	Chemicals, Concentration gradient, Separation (Technology), Nanofluidics, Fluorescence, Electrophoretic deposition
Abstract:	Previouswork has demonstrated the simultaneous concentration andseparation of proteins via a stable ion concentration gradient establishedwithin a nanochannel (InglisAngew. Chem., Int. Ed.2001, 50, 7546−7550). To gain a better understanding of how thisnovel technique works, we here examine experimentally and numericallyhow the underlying electric potential controlled ion concentrationgradients can be formed and controlled. Four nanochannel geometriesare considered. Measured fluorescence profiles, a direct indicatorof ion concentrations within the Tris–fluorescein buffer solution,closely match depth-averaged fluorescence profiles calculated fromthe simulations. The simulations include multiple reacting specieswithin the fluid bulk and surface wall charge regulation whereby thedeprotonation of silica-bound silanol groups is governed by the localpH. The three-dimensional system is simulated in two dimensions byaveraging the governing equations across the (varying) nanochannelwidth, allowing accurate numerical results to be generated for thecomputationally challenging high aspect ratio nanochannel geometries.An electrokinetic circuit analysis is incorporated to directly relatethe potential drop across the (simulated) nanochannel to that appliedacross the experimental chip device (which includes serially connectedmicrochannels). The merit of the thick double layer, potential-controlledconcentration gradient as a particle focusing and separation toolis discussed, linking this work to the previously presented proteintrapping experiments. We explain why stable traps are formed whenthe flow is in the opposite direction to the concentration gradient,allowing particle separation near the low concentration end of thenanochannel. We predict that tapered, rather than straight nanochannelsare better at separating particles of different electrophoretic mobilities. [ABSTRACT FROM AUTHOR]
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Database:	Engineering Source

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Abstract:	Previouswork has demonstrated the simultaneous concentration andseparation of proteins via a stable ion concentration gradient establishedwithin a nanochannel (InglisAngew. Chem., Int. Ed.2001, 50, 7546−7550). To gain a better understanding of how thisnovel technique works, we here examine experimentally and numericallyhow the underlying electric potential controlled ion concentrationgradients can be formed and controlled. Four nanochannel geometriesare considered. Measured fluorescence profiles, a direct indicatorof ion concentrations within the Tris–fluorescein buffer solution,closely match depth-averaged fluorescence profiles calculated fromthe simulations. The simulations include multiple reacting specieswithin the fluid bulk and surface wall charge regulation whereby thedeprotonation of silica-bound silanol groups is governed by the localpH. The three-dimensional system is simulated in two dimensions byaveraging the governing equations across the (varying) nanochannelwidth, allowing accurate numerical results to be generated for thecomputationally challenging high aspect ratio nanochannel geometries.An electrokinetic circuit analysis is incorporated to directly relatethe potential drop across the (simulated) nanochannel to that appliedacross the experimental chip device (which includes serially connectedmicrochannels). The merit of the thick double layer, potential-controlledconcentration gradient as a particle focusing and separation toolis discussed, linking this work to the previously presented proteintrapping experiments. We explain why stable traps are formed whenthe flow is in the opposite direction to the concentration gradient,allowing particle separation near the low concentration end of thenanochannel. We predict that tapered, rather than straight nanochannelsare better at separating particles of different electrophoretic mobilities. [ABSTRACT FROM AUTHOR]
ISSN:	07437463
DOI:	10.1021/la500206b