Advances in Microfluidic Impedance Cytometry for Electromechanical Characterization of Cells

Abstract

Single-cell analysis is extremely important for discovering unique characteristics of individual cells, identifying cell populations of interest, and understanding their behaviour during disease conditions. With the advent of flow cytometry - a well-established technique for counting, identifying and sorting cells, single-cell studies have progressed rapidly over the past few decades. Conventional flow cytometers are generally expensive pieces of machinery and utilize complex fluorescent detection systems for the analysis of single cells. Impedance cytometers, in contrast, offer label-free sample preparation, reduced experimental costs, lower sample volumes, simpler operation, and better portability. In the recent past, impedance cytometers have been used to analyse the electrical properties of numerous cell types in a rapid and efficient manner. However, its usage in understanding cell mechanical properties is sparsely explored. Early attempts in this aspect have been accompanied by major limitations in terms of device configurations, electrode geometries, and throughput. This thesis, thus, aims to overcome these limitations by exploring novel techniques for the electromechanical analysis of single-cells. To begin with, we propose a novel microfluidic impedance sensing platform capable of independently and simultaneously characterizing the electrical and mechanical properties of cells. Using healthy and chemically-stiffened erythrocytes, we validate the platform and discuss how it overcomes several challenges associated with traditional impedance cytometers. We then improve upon this platform by introducing a simple yet innovative flow-correction technique to circumvent flow-rate fluctuations in syringe-pump driven fluid flow, thereby accelerating data acquisition and improving accuracy. Using this upgraded platform, we offer valuable insight into the differences in electromechanical properties of human lymphocytes in healthy and diabetic individuals...