Current Monitoring in a Microchannel with Repeated Constrictions for Accurate Detection of Sample Location in Isotachophoresis

Abstract

We present a new method for accurate detection of sample location in peak mode isotachophoresis (ITP). The technique is based on the design of a microchannel with multiple constrictions and on detecting the passage of the ITP interface through these constrictions. We achieve this by monitoring the electric current across the channel, which exhibits sharp decreases as the ITP interface moves more rapidly through the higher current density constrictions. We show that cross-correlation between the electric current signal and a predefined step function is an effective method for detecting changes in the slope of the electric current curve in real-time and is robust to changes in the composition of the buffers. We demonstrate the use of the technique to deliver sample to a designated location in the channel with an accuracy as low as 50 μm. Importantly, the method does not require the use of any optics and thus can be used to monitor the location of unlabeled species for application in a variety of ITP assays.

Isotachophoresis-Based Surface Immunoassay

“…The CF-ITP mode benefits from a higher ratio between the accumulation and depletion time scales, which could be achieved by further optimizing the focusing rate. The SD-ITP mode, giving an approximately 10-fold higher LoD than the PO-ITP mode, would be the method of choice any implementation in which the location of the interface is dynamically trackable, e.g., by current monitoring or by image analysis. In contrast, the CF-ITP mode is recommended for applications in which the need of extreme limits of detection justifies a more complex setup to create and control the flow.…”

Oxidized Porous Silicon Nanostructures Enabling Electrokinetic Transport for Enhanced DNA Detection

“…Alternatively, the location of the ITP interface could be monitored by electric current readings. [ 64 ] The use of fl uorescently labeled DNA also presented diffi culties in determining the full dynamic range of the assay, as at low target concentrations (<1 × 10 −9 M ), the intensity of the ITP peak is too weak to be detected by our optical setup. Thus, the actual LoD of the ITP-PSiO 2 system may be lower than the values reported here.…”

Analytical capillary isotachophoresis after 50 years of development: Recent progress 2014–2016

“…The instrumentation allows investigating the separability of components and of the required capillary length for a specified analytical task, and is also able to provide feedback for performing realistic computer simulations. Karsenty et al described a new method for monitoring of the position of an ITP boundary in a microchannel containing several constrictions of lower cross‐section. The method is based on operation in constant voltage mode and monitoring the time dependence of electric current.…”