A low molecular weight cut-off polymer–silicate membrane for microfluidic applications

In this article, we report a novel approach to fabricating a low molecular weight cut-off membrane that could readily be employed for several microfluidic applications. The reported structure was created by selectively retaining a precursor solution [5% (w/v) maleic anhydride, 21% (v/v) (37:1) acrylamide/bisacrylamide, and 0.2% (w/v) VA-086 photoinitiator] in a chosen location of a microfluidic network via capillary forces and then photo-polymerizing the mixture. The pores in the resulting membrane were subsequently filled with 3-aminopropyltriethoxysilane, heated, and then treated with sodium silicate solution and heated again, giving a structure having reduced porosity. The composite membrane thus created has been shown to have a molecular weight cut-off that is at least an order of magnitude smaller than other photo-polymerized microfluidic membranes reported in the literature. Moreover, this polymer–silicate structure was observed to be capable of blocking electroosmotic flow, thereby generating a pressure gradient around its interface with an open microchannel upon application of an electric field across the microchannel-membrane junction. In this study, a fraction of the resulting hydrodynamic flow was successfully guided to an electric field free analysis channel to implement a pressure-driven assay. With our current design pressure-driven velocities, up to 1.8 mm/s was generated in the electric field free analysis channel for an applied voltage of 2 kV in the pumping section. Finally, the functionality of this integrated microfluidic device was demonstrated by implementing a reverse phase chromatographic separation using the pressure-driven flow generated on-chip.