Isotachophoretic phenomena in electric field gradient focusing: perspectives for sample preparation and bioassays

Isotachophoresis (ITP) and electric field gradient focusing (EFGF) are two powerful approaches for simultaneous focusing and separation of charged compounds. Remarkably, in many EFGF methods, isotachophoretic hallmarks have been found, including observations of plateau concentrations and contiguous analyte bands. We discuss the similarities between ITP and EFGF and describe promising possibilities to transfer the functionality and applications developed on one platform to other platforms. Of particular importance is the observation that single-electrolyte isotachophoretic separations with tunable ionic mobility window can be performed, as is illustrated with the example of depletion zone isotachophoresis (dzITP). By exploiting the rapid developments in micro- and nanofluidics, many interesting combinations of ITP and EFGF features can be achieved, yielding powerful analytical platforms for sample preparation, biomarker discovery, molecular interaction assays, drug screening, and clinical diagnostics.