Analyte transport past a nanofluidic intermediate electrode junction in a microfluidic device

Abstract

A glass microfluidic device is presented in which a microchannel is split into two regions with different electric fields by a nanochannel intermediate electrode junction formed by dielectric breakdown. The objective is to sink current through the nanochannel junction without sample loss or broadening of the band as it passes the junction. This type of performance is desired in many microfluidic applications, including the coupling of microchannel/CE with ESI-MS, electrochemical detection, and electric field gradient focusing. The voltage offsets in this study are suitable for microchannel/CE-ESI-MS. Imaging of the transport of model anions and cations through the junction indicates that the junction exhibits nanofluidic behavior and the mean depth of the nanochannel is estimated to be approximately 105 nm. The ion permselectivity of the nanochannel induces concentration polarization and enriched and depleted concentration polarization zones form on opposite sides of the nanochannel, altering the current and electric field distributions along the main microchannel. Anion transport efficiency past the junction was high, 96.0%, and varied little over the pH range of 4.0-8.0. In contrast, cation transport is much lower, and decreases from 72 to 11% from pH 4.0 to 8.0. Band broadening increases with increasing pH less than 70% over the pH range of 4.0-8.0. It is anticipated that this characterization will aid in the understanding and optimization of such junctions made from permselective membranes and porous glass.

On-Line Coupling of Chip-Electrochromatography and Ion Mobility Spectrometry

“…On the one hand, the integration of a photo-polymerized membrane is a rather complex process and on the other hand, these hydrogel membranes can degrade at the expense of long-term stability. To circumvent these challenges, we now developed a chip layout, implementing a nanofluidic junction instead of the hydrogel membrane, inspired by the work of Mao et al for MCE . Therefore, the column channel (II in Figure ) as well as the adjacent contact channel (III in Figure ) were filled with electrolyte and contacted using SST unions.…”

Ion concentration polarization near microchannel–nanochannel interfaces: Effect of pH value

“…Experimental evidence suggests that channels with a depth of less than ∼100 nm demonstrate a unique ion‐selective property at low ionic strengths since at such characteristic scales, the thickness of the electrical double layer (EDL) is nonnegligible compared to the nanochannel depth []. Therefore, when dilute background electrolyte (BGE) and sample species are introduced into such channels, they exhibit quite different phenomena from those observed within microchannels, including an ion exclusion‐enrichment effect [], ion depletion‐enrichment effect [], an amplified electrokinetic response [] near the microchannel–nanochannel interface, and so forth. These particular phenomena all are related to the ion selectivity of a nanochannel (or membrane).…”

Tuneable nanochannel formation for sample-in/answer-out devices

“…It is manifested as formation of fissures accompanied with increased ion transport and measured current. This has been reported for integrating nanochannels into microfluidic devices using different materials such as PDMS, 17,18 glass, 19,20 and toner. 21 Typically, the chip design includes a micrometer thick gap separating two microchannels filled with electrolyte solution.…”