(464a) A Pressure-Driven Separation Device with An Integrated Microfluidic Pump

Fluid and solute samples are commonly moved in microchannels using either electro-osmotic or pressure driven flow. While electroosmotic flow is relatively easier to control in microfluidic channels, pressure-driven flow is often applied in microfluidic applications where electro-osmotic flow is undesirable e.g. liquid chromatography. Steady pressure-driven flow has been realized in microfluidic channels using syringe pumps in this past. Although this method is easy to implement, the difficulty encountered with maintaining and dynamically controlling the pressure generated flows in this design have resulted in poor efficiency and reproducibility of separations. In this work, we report an on chip pressure generation capability that uses a porous membrane made using a sodium silicate precursor. The proposed micro-pump consists of 3 channel segments in a tee geometry one of which has the sodium silicate membrane. Our experimental study has shown that this membrane although has a high electrical conductivity tends to block electro-osmotic flow (EOF) very effectively. In this situation, by applying appropriate electric fields across this design, the EOF generated in one of the open channel segments was blocked by the sodium silicate membrane in the other, to generate a pressure-gradient in the system. The resulting pressure-driven flow could be then effectively maintained and guided into an electric field-free separation channel for performing pressure-driven chromatographic separations. More interestingly, it was shown that for an applied voltage in the system this pressure-driven velocity was independent of channel depth in the microfluidic network. This implies that the proposed strategy for generating pressure-gradients can be equally effective in realizing pressure-driven separations in micro- as well as nanoscale separation channels.