Optical control of electroosmosis

Principal Investigator: Pál Ormos
This project is part of the EU-FP6 cooperation ATOM-3D

Electroosmosis can be effectively used to manipulate fluid in microfluidic systems. The flow can be controlled by the geometry of the system, the zeta-potential of the channel walls, and the structure of the electric field itself which drives electroosmosis. In our concept we use light to dynamically modify the spatial structure of the electric field to control the flow. The conductivity of a photoconductor film parallel to a microfluidic channel is changed dynamically by appropriate illumination. A local increase in the conductivity upon excitation results in the reduction of the electric field in the corresponding microchannel region, and thus the local electroosmotic driving force. This way it is possible to realize a range of functions needed for the manipulation of fluids like switching of flow, (re)directing flow and mixing. The concept is demonstrated experimentally, modeled and interpreted.

Below you can see the microfluidic sample used in the experiments. As the photoactive layer we used CdS (cadmium-sulfidem, chemically deposited onto the glass surface). The sample was created by the soft lithography method. At the two ends of the microchannel there are two reservoirs open to the outside containing the electrodes.



Reference:
L. Oroszi, A. Dér, H. Kirei, V. Rakovics, and P. Ormos, Control of electroosmostic flow by light, Appl. Phys. Lett. 89 263508 (2006)