Microfluidic flow control setup for testing optical resonators Bisra, Gurpal; Johl, Shaina; Teoh, Wei Kee
Optical biosensors have many applications including biomedical research, healthcare, pharmaceuticals, environmental monitoring, homeland security, and the battlefield. Before these biosensors can be used effectively, they need to be characterized first with several fluids. The Microsystems and Nanotechnology Research Group in the Electrical and Computer Engineering Department at the University of British Columbia (UBC) currently does not efficiently characterize fluids. We have developed a prototype device for a microfluidic flow control system that will be used in experiments for testing optical resonators. This device is capable of mixing microliters of fluids and routing them to specified output channels. If ring resonators integrated with microfluidic channels are exposed to these output fluids, a shift in resonance peak can be correlated with the fluids’ known refractive indices, thus calibrating the sensor. The fabrication of the microfluidic flow system was based on three main objectives. The first objective was to implement a microfluidic control system. The user is now able to communicate and control up to 42 solenoid valves through a graphical user interface in MATLAB with this system. Our second objective was to fabricate a microfluidic chip that can mix and deliver different concentrations of two reagents to 4-8 output channels. Three different microfluidic chips were designed, using CleWin software, and were fabricated into PDMS microfluidic chips. The third and final objective was to enhance the current mechanical fixture housing the complete flow control system and biosensor test chip. The newly built fixture was designed using SolidWorks software and is more robust, compact, and organized. The benefits of a new fixture consist of allowing the entire system to be more accessible to the user and the system is more transportable than the current setup. In order to have achieved these objectives, we required access to several technical resources that were available at the UBC campus. The computers in Kaiser 4060 had MATLAB, CleWin and PCB Artist programs that were required to construct the various parts of the prototype. We also required access to AMPEL 146 to fabricate the different layers of the mixing chip. Some notable conclusions for this project are that the PCB is capable of running 4 peristaltic pumps at different rates simultaneously and the user does not need to figure out which solenoid valves to actuate to achieve a certain routing scheme. In particular, a three-valve peristaltic pump, using the standalone router, was used to characterize the flow rate of peristaltic pumps. The authors achieved a lower limit of flow rate was 0.0445nL/s and an upper limit of flow rate was 1.519nL/s. Furthermore, the mechanical fixture was fabricated and all components can be attached onto it once the remaining solenoid valves and manifolds arrive. The authors have made a few recommendations at the end of the report. First, during the mask design step, care should be taken such that the features of the microfluidic chip are not too close to the edge of the silicon wafer. Also, due to restraints in time, the authors were unable to characterize the mixing channels. These tests should be carried out in the future. Now that our project is complete, we anticipate that our device will be able to successfully deliver mixtures of concentrations of reagents to our project sponsor’s ring resonator biosensor apparatus. Thus, the benefit of fabricating the microfluidic flow system is that it will expedite the characterization process of the ring resonators. The resulting prototype will be delivered to the client in a form that will be easily operable by researchers and non-technical staff of the Microsystems and Nanotechnology Research Group in the Electrical and Computer Engineering Department at UBC. In particular, Dr. Karen Cheung’s graduate students can characterize their ring resonator designs more efficiently.
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