High‐sensitivity detection using isotachophoresis with variable cross‐section geometry

Abstract

We present a theoretical and experimental study on increasing the sensitivity of ITP assays by varying channel cross-section. We present a simple, unsteady, diffusion-free model for plateau mode ITP in channels with axially varying cross-section. Our model takes into account detailed chemical equilibrium calculations and handles arbitrary variations in channel cross-section. We have validated our model with numerical simulations of a more comprehensive model of ITP. We show that using strongly convergent channels can lead to a large increase in sensitivity and simultaneous reduction in assay time, compared to uniform cross-section channels. We have validated our theoretical predictions with detailed experiments by varying channel geometry and analyte concentrations. We show the effectiveness of using strongly convergent channels by demonstrating indirect fluorescence detection with a sensitivity of 100 nM. We also present simple analytical relations for dependence of zone length and assay time on geometric parameters of strongly convergent channels. Our theoretical analysis and experimental validations provide useful guidelines on optimizing chip geometry for maximum sensitivity under constraints of required assay time, chip area and power supply.

Recent advances in enhancing the sensitivity of electrophoresis and electrochromatography in capillaries and microchips (2010–2012)

“…In cationic ITP mode, similar concentration factor was achieved for the biomarker cardiac troponin I and its phosphorylated forms, which were successfully separated from human serum in the presence of serum proteins . This approach was also used with indirect fluorescence detection by Bahga et al who also performed numerical simulations to validate the model and the effectiveness was demonstrated for bis‐tris, as a model compound, with a sensitivity of 100 nM . According to the results presented, short channels with decreasing dimensions offered comparable sensitivity to that achieved with longer uniform channels within shorter analysis time.…”

Microfluidic isotachophoresis: A review

“…The mathematical equations, which assume that the acid–base reactions are instantaneous, pay particular attention to calculating total concentrations of species rather than individual ionic states; and boundary conditions that allow solution in a moving frame of reference were described in a later paper . SPRESSO now includes an extended Onsager–Fuoss correction to determine effective electrophoretic mobilities, and an extended Debye–Hückel formula to calculate and correct ionic activities as well as modifying the governing equations to take into account variable cross‐sectional area geometries in the context of a 1D geometry . GENTRANS has been modified to handle ITP separations with a complexing agent and a version of SIMUL (SIMUL 5 Complex) can simulate affinity ZE with a complexing agent .…”

Recent progress in analytical capillary isotachophoresis

“…Bagha et al reinvestigated the column coupling (volume coupling) technique from the viewpoint of constraints on geometry, detection time, and applied voltage that are important for on‐chip systems. Explicit formulas for resulting zone length and detection time were derived and the theory exemplified by computer simulations and experiments.…”