Development of a Low-Cost Electrical Impedance-Based Microflow Cytometer

Sickle Cell Disease (SCD) is a genetic condition caused by a mutated hemoglobin molecule (HbS) found in red blood cells (RBCs). HbS polymerizes in low oxygen environments and contribute to painful vaso-occlusion in patients. Laboratory diagnosis of SCD is typically made by detection of the presence of sickle cells by peripheral blood smear, and presence of HbS by electrophoresis and high-performance liquid chromatography. Recently, flow cytometry technique in companion with sickling assays has demonstrated the capability in quantitative measurements of sickle cells at single-cell level, using software algorithm for cell-imaging analysis (Van Beers et. al. American Journal of Hematology 2014), and electrical impedance (Liu et. al. Sensors and Actuators B: Chemical 2018). Here, we show a portable, cost-efficient electrical impedance-based sensor and its capability to be used in conjunction with microfluidics-based sickling assay for microflow cytometry of sickle cells.

The impedance microflow cytometer is based on a commercially available integrated circuit (IC), the AD5933. Using a microcontroller and additional circuitry on a custom designed printed circuit board, we are able to produce sinusoidal signals of up to 100kHz in frequency and sample up to 200 data points per second, at a cost under $60 in materials to create. The impedance measurement range is optimized to work in companion with microfluidic chips in general. In order to measure sickle cells, the impedance microflow cytometer is used in companion with our unique Polydimethylsiloxane (PDMS) microfluidic cell sickling assay (Du et. al. PNAS 2014). Cells are suspended in phosphate buffered saline (PBS) medium and move in the microchannel using a pressure driven flow. Impedance measurement is achieved using two Ti/Au electrodes embedded in the microchannel as cells flow past the electrodes. Data is captured and made available for post processing using a customized MATLAB script. RBCs from healthy donors and SCD patients were used to demonstrate the capability of the developed system. The results showed that our system can separate between normal RBCs and sickle cells, as well as between sickled and unsickled cells. The performance in detection of sickle cells is comparable to a commercial impedance analyzer. This proof-of-concept design aims to minimize the physical space needed for cytometry as well as bring affordable and reliable cytometry results within its given limitations.

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