Micromachined Coulter counter for dynamic impedance study of time sensitive cells

This paper describes the design, modeling, fabrication and characterization MEMS Coulter counter that can detect and monitor the dynamic cell impedance changes in situ as a function of time after mixing isolated cell populations with different extracellular media within 0.3 s 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, which has not been reported before. The devices were tested with both fluidic and electrical functionality using yeast cells in cryoprotectant agent (diluted dimethyl sulfoxide), red blood cells, microbeads with different dimensions, and dyed fluids. The results demonstrate rapid changes of cell volume within the first 0.6 s after mixing followed by a stable and a fixed cell volume. The micromixer was initially simulated using COMSOL finite element tool. Image processing technique was used to quantitatively evaluate mixing efficiency by analyzing color intensities variation of captured images of 2 dyed fluids mixed in the channel at flow rates between 0.1-0.4 μl/min, the mixing efficiencies were between 87 %-95 %, respectively.