Si-supported mesoporous and microporous oxide interconnects as electrophoretic gates for application in microfluidic devices

Microfluidic analysis systems are becoming an important technology in the field of analytical chemistry. An expanding area is concerned with the control of fluids and species in microchannels; by means of an electric field. This paper discusses a new class of Si-compatible porous oxide interconnects for gateable transport of ions. The integration of such thin oxide films in microfluidics devices has been hampered in the past by the compatibility of oxides with silicon technology. A general fabrication method is given for the manufacture of silicon microsieve support structures by micromachining, on which a thin oxide layer is deposited by the spin-coating method. The deposition method was used for constructing gamma-alumina, MCM-48 silica, and amorphous titania films on the support structures, from both water-based and solvent-based oxide sols. The final structures can be applied as microporous and mesoporous interconnecting walls between two microchannels. It is demonstrated that the oxide interconnects can be operated as ion-selective electrophoretic gates. The interconnects suppress Fick diffusion of both charged and uncharged species, so that they can be utilized as ionic gates with complete external control over the transport rates of anionic and cationic species, thus realizing the possibility for implementation of these Si-compatible oxide interconnects in microchip analyses for use as dosing valves or sensors.