title: Sodium silicate based sol-gel structures for generating pressure-driven flow in microfluidic channels.
abstract: In this article, we report the design of a microchip based hydraulic pump that employs a sodium silicate derived sol-gel structure for generating pressure-driven flow within a microfluidic network. The reported sol-gel structure was fabricated in a chosen location of our device by selectively retaining sodium silicate solution within a sub-micrometer deep segment via capillary forces, and then providing the precursor material appropriate thermal treatment. It was shown that while the molecular weight cut-off for these membranes is at least an order of magnitude smaller than their photo-polymerized counterparts, their electrical conductance is significant. Moreover, unlike their polymeric counterparts these structures were found to be capable of blocking electroosmotic flow, thereby generating a pressure-gradient around their interface with an open microchannel upon application of an electric field across the microchannel-membrane junction. In this work, a fraction of the resulting hydrodynamic flow was successfully guided to an electric field-free analysis channel to implement a pressure-driven assay. Our experiments show that the pressure-driven velocity produced in the analysis channel of our device varied linearly with the voltage applied across the sol-gel membrane and was nearly independent of the cross-sectional dimensions of the membrane and the microfluidic channels. With our current design pressure-driven velocities up to 1.7 mm/s were generated for an applied voltage of 2 kV, which easily covers the range of flow speeds that can minimize the plate height in most microfluidic separations. Finally, the functionality of our device was demonstrated by implementing a reverse phase chromatographic separation in the analysis channel of our device using the pressure-driven flow generated on-chip.
authors.affiliation: Department of Chemistry, University of Wyoming, 1000 East University Avenue, Laramie, WY 82071, USA.
authors.forename: Gwendoline M
authors.initials: GM
authors.lastname: Toh
authors.forename: Robert C
authors.initials: RC
authors.lastname: Corcoran
authors.forename: Debashis
authors.initials: D
authors.lastname: Dutta
mesh_terms: D004867:Equipment Design; D044085:Microfluidics / Q000295:instrumentation*; D017640:Silicates / Q000737:chemistry*
chemical_list: D017640:Silicates; C005691:sodium silicate