MEMS Coulter counter for dynamic impedance measurement of time sensitive cells
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] In this research, a MEMS Coulter counter is designed, modeled, fabricated and characterized, which can detect and monitor the dynamic cell impedance changes in situ as a function of time and cellular volumetric changes after mixing isolated cell populations with different extracellular media within 0.2 second from the start of mixing. The novelty of this design is the use of multi-electrodes with vertical sidewalls to enable the measurements of time sensitive cells with significantly enhanced sensitivity as well as the integration of passive mixing, focusing of cells in line and impedance detection using the vertical electrodes on a single chip that is made mainly using multilayer of SU-8. The device consists of a mixer with a T-shaped and serpentine shape channels, dielectrophoretic focusing region, and electrical impedance detection region. Multiple pairs of electrodes were distributed throughout the microchannel and the impedance of cells was monitored along the whole Coulter channel as cells pass through. The mixing, focusing and sensing functionalities were first simulated using COMSOL finite element tool. The devices were then fabricated using a series of surface micromachining, SU-8 and PDMS processes on glass slides. The fabricated devices were tested by injecting saline water with different standard size latex microbeads as well as various types of cells including fibroblast cells, red blood cells and yeast cells were mixed with cryoprotectant agent and phosphate buffered solution. To quantitatively evaluate mixing efficiency, image processing technique was used to analyze color intensities variation of captured images of 2 dyed fluids mixed in the channel at different flow rates. Both fluidic and electrical testing results validate the performance of the microfabricated Coulter counter.
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