Design and Fabrication of Microfluidic Chip for Temperature Control Applications in Biomedical

This paper proposes an On-chip microfluidic system specially designed for temperature control reactions in biomedical, for example, polymerase chain reaction (PCR) applications. The microfluidic chip and thin film heaters have been designed using COMSOL Multiphysics. The proposed system is fabricated on a glass substrate of size 5×5 cm², taking advantage of the thermally conductive and electrically insulating substrate. The microfluidic system made in Polydimethylsiloxane (PDMS) consists of a reaction chamber for PCR, a microchannel for fluid handling, and two thermally actuated valves for fluid control. On the other side of the glass substrate, it has three thin film metal heaters made in Cr/Al/Cr layers which are intergraded with the microfluidic network over the glass substrate. The middle heater is used for performing PCR reactions and the left and right heaters are fabricated for the actuation of valves. Therefore, the channel can be closed, and the PCR chamber can become isolated for the reaction to take place. However, after closing the channel, the shape mismatching between the rectangular cross-section of the channel and the balloon-shaped valve membrane (after actuation) results in the sample's leakage. Therefore, after some time the reaction chamber becomes empty which leads to the device failure. To overcome this issue, a semicircular cross-section PDMS channel has also been made using the AZ 40 XT positive photoresist mold. The fabricated microfluidic network has been integrated with the thin film heaters over the glass substrate using the different thin and thick film technological steps. Finally, the system has been tested for further verification of leakage from the microfluidic channel.