26 August 2005 Optical control of electro-osmotic flow
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Electro-osmotic pumping is an efficient way to move fluids in microfluidic systems. It is driven by the interaction of the Debye layer formed in the vicinity of the charged channel wall with a tangential electric field. The key parameters that determine the flow properties are the zeta potential of the surface and the electric field that drives the flow. Consequently, the flow can be controlled by appropriately modifying these parameters. Controlling the charge on the channel wall makes it possible to modify fluid flow. Likewise, the electric field close to the surface can be modified by changing the conductivity of the surface. The surface charge of appropriate materials can be changed by light illumination: the application of this phenomenon offers the possibility to optically control flow parameters. We have tested this possibility with several light sensitive surfaces. In the class of materials that change their charge upon illumination TiO2, a well known photoactive material was investigated. Experiments were also performed with the protein bacteriorhodopsin, known to change its surface charge following the release of protons into the solvent upon illumination. CdS was tested as the photoconductive material to modify the electric field by light. Linear microfluidic channels were prepared by soft lithography: a PDMS mold was placed upon a planar glass surface so that a rectangular cross section channel was formed upon the glass. The photosensitive materials covered the bottom glass surface. The experiments show that the flow can be readily modulated by illumination. The results demonstrate that it is possible to dynamically control microfluidic flow, opening up the prospect to create optically controlled complex microfluidic networks.
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Huba Kirei, Huba Kirei, Andras Der, Andras Der, Laszlo Oroszi, Laszlo Oroszi, Karpat Ferencz, Karpat Ferencz, Vilmos Rakovics, Vilmos Rakovics, Pal Ormos, Pal Ormos, } "Optical control of electro-osmotic flow", Proc. SPIE 5930, Optical Trapping and Optical Micromanipulation II, 59301I (26 August 2005); doi: 10.1117/12.616240; https://doi.org/10.1117/12.616240

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