Electrokinetic transport and separations in fluidic nanochannels

Abstract

This article presents a summary of theory, experimental studies, and results for the electrokinetic transport in small fluidic nanochannels. The main focus is on the effect of the electric double layer on the EOF, electric current, and electrophoresis of charged analytes. The double layer thickness can be of the same order as the width of the nanochannels, which has an impact on the transport by shaping the fluid velocity profile, local distributions of the electrolytes, and charged analytes. Our theoretical consideration is limited to continuum analysis where the equations of classical hydrodynamics and electrodynamics still apply. We show that small channels may lead to qualitatively new effects like selective ionic transport based on charge number as well as different modes for molecular separation. These new possibilities together with the rapid development of nanofabrication capabilities lead to an extensive experimental effort to utilize nanochannels for a variety of applications, which are also discussed and analyzed in this review.

Electroosmotic flow in single PDMS nanochannels

“…However, as the dimensions of nanochannels are comparable with the thickness of EDL, EDLs may overlap and consequently many new transport phenomena such as current rectification [1][2][3][4] , ion enrichment and depletion 5 , new dynamics of pressure driven flow [6][7][8] have been discovered. These new transport phenomena facilitate various novel applications and studies of the nanofluidics [9][10][11][12] . Theoretically, in nanochannels with overlapped EDLs, traditional Poisson-Boltzmann equation and Helmholtz-Smoluchowski equation used in microchannel systems are not applicable anymore 13 .…”

Dielectric properties of a single nanochannel investigated by high-frequency impedance spectroscopy

“…[1], [2], [3], [4], [5], [6], [7], [8], [9] In such systems characterized by at least one nanometer dimension, the role of the surface charge is exacerbated, [10], [11] and new phenomena such as surface-charge mediated transport and permselectivity occur. The unbalanced ionic transport between anionic and cationic species through a nanofluidic structures initiates a polarization effect related to the concentration domain, which can be applied for focusing and locally preconcentrate ionic species.…”

Investigation on entrance length for electroosmotic flow in circular and noncircular cross section nanochannel

“…With the assumption of thin Debye layers, an electroosmotic slip velocity parallel to the channel walls is produced. The resulting flow velocity is described as follows, μ ε ζ E vEOF ( 2 ) 080002-3 where ε is the permittivity of the solution, μ is the viscosity, ζ is the zeta potential at the channel wall and E is the applied electric field strength.…”

“…Therefore, fluid flow in small-scale studies with the aid of the prominent forces on the wall surface due to the EDL has gained much interest among researchers. This study includes the manipulation of wall surface profile by using an electric field to perform a various potential function comprising separation (2), ion-selective channel (3), or similar fluids reactions in microfluidic devices such as fluids pump, actuators and bioparticle diffusers/nozzles (4).…”