We have shown many potential application to electronic control of concentration and mixing of biomolecules in microfluidic systems, e.g reaction control in chemical replication systems, as electronic barriers to control diffusion or to adjust systems which are strongly dependent on concentration like the formation of micelles at the critical micelle concentration like the electronically controlled µ-fluidic gradient chip for phase screening and so on. Moreover, the developed device could be used as a pumping device as well used e.g. for the controlled dosing of catalytic/initiator chemicals in the fan-reactor.
The current experimental data confirm that the integrated electrodes of the Chemical Microprocessor - ChµP induce flow velocity changes within a homogeneous fluid and a rapid mixing effect if an alternating electric field is provided. Furthermore, the experimental results demonstrate that the developed active mixers permit a high degree of control over the fluid flow and an efficient mixing effect.
We make use of the electronic control of concentration and mixing to follow kinetics of ligation or replication of short oligonucleotides in microfluidic systems using FRET (Fluorescence Resonance Energy Transfer). Therefore we studied the behaviour of two pairs of oligonucleotides either labelled with Alexa 488 or Atto 590 dye, which are known as effective FRET fluorophores.
The experiments for DNA hybridization in a µ-fluidic compartment using FRET transfer in our microfluidic "H"-structure element were performed using a FRET-pair depicted in the opposite figure. The microfluidic "H”"-shaped arrangement consists of two inlet-channels, which are connected by a shallow connection channel (1 µm). The interconnecting channel contains four electrodes and one circular reaction chamber.
The inlet channels are flushed with buffered solutions of Alexa-oligomer (1 µM) and Atto-oligomer (2 µM) in a buffer mixture of 50 mM HIS and 50 mM NaCl with a flow-rate of 4 µL/h at temperature 10°C. The large grey-scale picture is taken by an EMCCD-camera (grey scales) and the small inset with a common digital camera. The experiments showed that in the reaction chamber, where both substrates get mixed the hybridization reaction results in fluorescence intensity and colour changes. The fluorescence images are created within the wavelength from 600-650 nm using a special emission filter (Semrock HC 624/40). By alternate cycling of the electrode potentials either the acceptor (dark red fluorescence of Atto 590) labelled oligonucleotide or the donor (intensive green fluorescence of Alexa 488) labelled oligonucleotide are moved by electroosmotic flow into the reaction chamber resulting in an increase of fluorescence intensity. This finding and the orange fluorescence inside the µ-fluidic compartment (reaction chamber) indicate that an energy-transfer from the Alexa-Donor to the Atto-Acceptor (FRET) occurs.