Tunable Ionic Mobility Filter for Depletion Zone Isotachophoresis

Abstract

We present a novel concept of filtering based on depletion zone isotachophoresis (dzITP). In the micro/nanofluidic filter, compounds are separated according to isotachophoretic principles and simultaneously released selectively along a nanochannel-induced depletion zone. Thus, a tunable low-pass ionic mobility filter is realized. We demonstrate quantitative control of the release of fluorescent compounds through the filter using current and voltage actuation. Two modes of operation are presented. In continuous mode, supply, focusing, and separation are synchronized with continuous compound release, resulting in trapping of specific compounds. In pulsed mode, voltage pulses result in release of discrete zones. The dzITP filter was used to enhance detection of 6-carboxyfluorescein 4-fold over fluorescein, even though it had 250× lower starting concentration. Moreover, specific high-mobility analytes were extracted and enriched from diluted raw urine, using fluorescein as an ionic mobility cutoff marker and as a tracer for indirect detection. Tunable ionic filtering is a simple but essential addition to the capabilities of dzITP as a versatile toolkit for biochemical assays.

Droplet encapsulation of electrokinetically-focused analytes without loss of resolution

“…Since then a vast amount of research has been performed in ion concentration polarization (ICP) and ICPF. 5,17,[21][22][23][24][25][26][27][28][29][30] We refer the reader to a short theoretical background of ICPF in the ESI † in order to define the requirements of the droplet generator. For a deeper theoretical background of ICPF the reader is referred to our previous work 1 or the work of Ouyang et al 31 and the more recent work of Gong et al 6,7 There are two operating modes in ICPF namely peak and plateau mode.…”

Continuous focusing, fractionation and extraction of anionic analytes in a microfluidic chip

“…Such a compound is usually named electrophoretic spacer which has been previously reported in ICPF. 3,40…”

“…Since its introduction vast amount of research has been performed with this technique, where Quist et al 2 demonstrated that apart from concentration also separation occurred. [3][4][5][6][7]34 Though the technique offers a very powerful and simple analytical tool, a disadvantage is that the focused and separated analytes are "trapped" inside the chip in picoliter volumes. Further analysis, for example by mass spectrometry, thus is impossible.…”

Recent advances in enhancing the sensitivity of electrophoresis and electrochromatography in capillaries and microchips (2012–2014)

“…In the previous review, the introduction of depletion zone ITP (dzITP) by Quist et al was highlighted as an interesting approach to sample treatment because it leverages CF gradient focusing to create a depletion zone using only a single electrolyte. Since then, the authors used this approach with a novel filtering principle in combination with dzITP . The filtering method is based on the balance of fluxes such that selectivity can be obtained as the dzITP orders compounds into distinct zones before they pass the depletion zone.…”