Micro contactor based on isotachophoretic sample transport

It is demonstrated how isotachophoresis (ITP) in a microfluidic device may be utilized to bring two small sample volumes into contact in a well-controlled manner. The ITP contactor serves a similar purpose as micromixers that are designed to mix two species rapidly in a microfluidic channel. In contrast to many micromixers, the ITP contactor does not require complex channel architectures and allows a sample processing in the spirit of "digital microfluidics'', i.e. the samples always remain in a compact volume. It is shown that the ITP zone transport through microchannels proceeds in a reproducible and predictable manner, and that the sample trajectories follow simple relationships obtained from Ohm's law. Firstly, the micro contactor can be used to synchronize two ITP zones having reached a channel at different points in time. Secondly, fulfilling its actual purpose it is capable of bringing two samples in molecular contact via an interpenetration of ITP zones. It is demonstrated that the contacting time is proportional to the ITP zone extension. This opens up the possibility of using that type of device as a special type of micromixer with "mixing times'' significantly below one second and an option to regulate the duration of contact through specific parameters such as the sample volume. Finally, it is shown how the micro contactor can be utilized to conduct a hybridization reaction between two ITP zones containing complementary DNA strands.