An In-Silico investigation into the Electrode Design in Impedance Flow Cytometry
The aim of this work is to investigate the impact of the structural parameter on the signal of the impedance based microfluidic flow cytometer for cell detection. A well-established optical technique for counting, identifying and sorting cells is flow cyto-fluorimetry, which is an expensive technique, complex to operate and unsuited for handling small sample volumes. However, Impedance based microfluidic cytometers based on Coulter principle e.g. Hematology have recently shown a great potential for point of care biosensors. Label free technique is achieved by using AC instead of DC. Multi-frequency impedance measurements can give multi-parametric, high-content data that can be used to distinguish cell types. Today, the developmental aim for microfluidic systems is to reach the same sensitivity and capability for multi-parametric analyses as delivered by conventional flow cytometers. Many efforts have been made to improve existing devices and to create new miniaturized high-end instruments. In order to design such miniaturised device, a detailed study on the different structural parameters of the sensor has to be taken into consideration to evaluate its impact on sensitivity. The different structural parameters would include size of the electrode, distance between two electrodes, cross sectional area of microfluidic channel and morphology of the cell. The main feature of this paper is in-silico performance investigation of the differential impedance based flow cytometer is done with a finite element method (FEM) using AC/DC module of COMSOL Multiphysics 5.3a. In conventional design, the two configurations (coplanar and parallel facing microelectrode) which are generally used are integrated below the microfluidic channel. An electric field is generated by electric potential or electric current stimuli is used to measure the differential impedance. Parallel facing microelectrode is highly influenced by the cross electric field however it is more sensitive to small cell size (therefore preferred over coplanar configuration). Thus, the gap between the electrodes varying from 1µm to 50 µm is analysed for optimal design of differential impedance measurement to minimize the interference of neighbouring electrode. Multi-frequency impedance measurements in the frequency spectrum of 100 kHz-10 MHz can provide multi-parametric information to characterize different kinds of cells. Nonetheless, at low frequencies (below 500 kHz), the cell film demonstrating a capacitive conductance, offers vital hindrance to electric field and the impedance bounty reveals the cell size. At higher frequencies of above 2-3 MHz, the membrane is insignificantly polarized, and estimations provide information about cytoplasm conductivity and permittivity. Results and analysis will be presented in the final paper.
