R.B. Fair, L.J. Chen
Keywords: lab-on-chip, sensor, microfluidics, cell analysis
Summary:The use of a digital microfluidic platform is described for performing cell analysis. A unique challenge in cell analysis is the detection of existing cells in a complex sample when the concentration of target cells is low and the sample volume is large, resulting in poor signal-to-noise ratios. Thus, improved cell concentrations can be achieved by selective cell extraction from milliliter volumes followed by concentration in microliter volumes, which are suitable for microfluidics. Once target cell extraction is completed, the concentrated are loaded on chip. For steps performed on chip, magnetic bead manipulation, fluorescent signal measurement and immunological binding must be compatible. Magnetic bead manipulation uses the structure of half-circle shaped current-carrying wires embedded in an actuation electrode of an EWD device. The current wire structure serves as a micro-electromagnet, which is capable of collecting and concentrating labeled magnetic beads to increase the SNR of sample detection. Immunological binding requirements make it necessary to use reaction kits that ensured the compatibility of target cells, magnetic bead function and EWD function. The magnetic bead choice ensures the binding efficiency and survivability of target cells. The SNR of fluorescent measurements is enhanced 30 times by concentrating magnetic beads into a reduced sensing area of tens of square microns. Theoretical limitations of the entire sparse sample detection system is as low as 1 Colony Forming Unit/mL (CFU/mL).