(614b) Field Effect Flow Control In Pdms Microchips

In Lab-on-a-Chip microfluidic devices, electroosmotic flows (EOF) are most widely used to drive samples. The magnitude of EOF velocity in a microchip can be controlled either by changing the external electric field applied along the flow direction or by modifying the electrokinetic potential at the Stern plane (also known as zeta potential). It is relatively easy to control the overall flow rate in a straight microchannel by adjusting the external electric field applied in the flow direction. This kind of control is generally global, and it affects the entire electric field region. However, it cannot be applied to a local area of interest or in complex micro-geometries. But, the selective manipulation of zeta potential has promises to control the flow locally. To test this hypothesis, a field-effect transistor is developed to alter the zeta potential in microfluidic chips. Here, microchannel structures and field-effect transistors are formed on poly-di-methyl siloxane (PDMS) using soft lithography techniques, and a micro particle image velocimetry technique is used to obtain high resolution velocity distribution in the controlled region. The flow control is observed at relatively low gate voltage (less than 50 [V]), and this local flow control is primarily due to current leakage through the interface between PDMS and glass layers. A leakage capacitance model is introduced to estimate the modified zeta potential for the straight channel case, and an excellent agreement is obtained between the predicted and experimental zeta potential results. This leakage-current based field-effect is then applied to a T-channel junction to control flow in the branch channel. Experiments show that the amount of discharge in the branch channel can be controlled by modulating gate voltage.