Isotachophoresis with oscillating sample zones to control the mixing of co-focused species

Microfluidic isotachophoresis (ITP) is a powerful technique that can significantly increase the reaction rate of low-concentration species by co-focusing them in a narrow sample zone. It uses strong gradients in the electric field between two electrolytes to increase the local concentration of the reactants by several orders of magnitude. Therefore, ITP has been utilized to reduce the reaction time in various bioanalytical assays. However, in conventional ITP, it is hardly possible to manipulate the spatial distribution of the reacting species and thus to control the course of a reaction. Here we present experiments that introduce a new approach to compensate this disadvantage. Two samples are initially focused and separated by a spacer in ITP with a DC electric field. By superimposing an oscillating field component with sufficiently high amplitude to the DC field, the spatial overlap of their concentration profiles, i.e. their mixing, is temporarily increased due to electromigration dispersion. The time average of this overlap can be precisely controlled by varying the frequency and amplitude of the oscillation. We suggest that this can be transferred to reactions involving ionic species with sufficiently different electrophoretic mobilities. Tuning the parameters of the oscillatory electric field should allow to directly influence the corresponding reaction rate.