(291e) A Spiral-Shaped Microfluidic Separation Channel with Integrated Microelectrodes for Cell Sorting and Position Analysis.

Cell/particle soring within a heterogeneous population is a crucial preparatory step in many science and medicine fields, including hematology, immunology, health/disease diagnosis, drug development, and cancer research. Various passive cell separation microfluidic devices have been developed in the domain of microfluidics. In these devices, heterogeneous cells develop distinctive migration patterns according to their physical properties (e.g., size and shape) inside specially designed microfluidic channels while under pressure-driven flow. As a result, cells elute from the channel at different rates and positions (like liquid chromatography but with cells). These devices have many unique advantages over conventional cell separation methods (e.g., size-based filtration), including low cost, small footprint, ease of instrumentation, label-free, reduced sample waste, and high sample throughput. However, many devices still require external methods, such as high-speed camera imaging or fluorescent flow cytometry, to analyze separated cells.

In contrast, impedance flow cytometry (IFC) analyzes cells based on the impedance change caused by cells traversing across electrodes. The ease of integration into the microfluidic channel and other advantages make the IFC an ideal end-column-detection method for these devices. In this work, we demonstrated for the first time a cell sorting device combining a spiral-shaped inertial-based microfluidic channel for cell separation and integrated microelectrodes for cell counting and focusing efficiency identification. A unique electrode design was proposed to detect both cells and their lateral positions inside the channel.

Methods and Results

Polystyrene microspheres were injected into the channel, while a high-speed camera was used to record their trajectories across the electrodes. The detector output amplitude signals were extrapolated to measure the positions of individual particles. The ability of the spiral-shaped microfluidic channel to focus particles was examined against various sample flowrates by measuring individual microspheres’ lateral positions. The focusing of 10 μm microspheres was around 20 µL/min flowrate. A low (500 kHz) and a high (4 MHz) frequencies were applied to the electrodes to detect Giardia and cryptosporidium cysts electrically. The difference in the electrical amplitude and phase ratio was found to be most prominent at low frequencies, demonstrating the differentiation of the two parasite types using the electrodes.

Significance

The preliminary results from our work represent an advance in microfluidic cell sorting with onboard cell detection while indicating an alternative to the gold standard flow cytometry. The proposed electrodes can be a universal detector for various microfluidic chromatography or separation systems. While having a comparably small footprint, the device is readily field deployable. For instance, it could be utilized to monitor the presence of bacteria and parasites in drinking or recreational water.