SiO2-Coated Porous Anodic Alumina Membrane for Electroosmotic Pumping

Abstract

Electroosmotic pumping has been extensively used in biomedical lab-on-a-chip devices and micropumps for critical applications such as microelectronic cooling. In many applications, a high flow rate is a key requirement in desired performance so constant efforts have been made to increase the pumping flow rate through unit area to achieve the compact design. We report here an attempt of using SiO2-coated anodic porous alumina membrane as the material to achieve high electroosmotic pumping flow rate. High quality porous alumina membranes of controllable pore diameter in the range of 20-300 nm and pore length of 60 - 100 μm have been fabricated with electrochemical anodization. The pores are uniform and hexagonally packed with a high porosity of up to 50% and a tortuosity of a bare minimum of unity. In addition, the inner surface of the pores could be conformally coated with a thin layer (~ 5 nm) of SiO2 with sol-gel chemistry to achieve a high zeta potential. Scanning electron microscopy of the cross section of the membrane verified these facts. Electroosmotic pumping performance of these membranes has been investigated using standard relevant aqueous electrolyte buffer solutions and results showed that SiO2-coated porous alumina could achieve a higher flow rate compared with other microporous materials such as glass frit and porous silicon reported in the literature.