Characterization of a Spiral Microfluidic Focusing Device for Continuous Single Cell Impedance-Based Cytometry Applications

A major focus in the field of cell characterization is the quantification of cell dielectric properties in order to develop low-cost, portable microfluidic devices that can, among other things, perform point-of-care detection of rare diseases and complete blood counts. Impedance-based cytometry has become an advantageous tool to ascertain these properties, wherein it is important that cells pass through the same point in a channel cross-section one at a time to ensure accurate and repeatable readings. This study documents the assessment of an 8-loop 160 μm (W) x 80 μm (H) spiral microchannel used to focus 10 μm polystyrene particles. In addition, the distances between focused particles are measured in order to optimize measurement electrode geometries in future devices. Particles were observed through an inverted microscope via fluorescent illumination and photographed with a high-resolution digital SLR camera. Quantification of focusing effectiveness and separation distances versus varying flow rates and volume fractions was performed in MATLAB. Flow rate and volume fraction were shown to play strong roles in the focusing effectiveness and how the particles distribute themselves within the microchannel. The simple nature of the particle focusing ability of this device makes it an excellent candidate for integration into lab-on-a-chip impedance cytometers.