Abstract
Precise measurement of single-cell biophysical properties (e.g., mechanical, electrical properties and cell size) can yield useful information on the physiological and pathological state of cells. Mechanical properties of cells, reflective of various biochemical characteristics such as gene expression and cytoskeleton, are promising label-free biomarkers for studying and characterizing cells. Electrical properties of cells, dependent on the cellular structure and content, are also label-free indicators of cell states and phenotypes. In addition, lateral position can signify the biophysical properties of target cells under applied forces in the microfluidic channel and evaluate the efficiency of cell focusing and sorting system. In this dissertation, we have developed microfluidic impedance flow cytometries capable of characterizing the single-cell mechanical and electrical properties simultaneously, and determining the lateral position and size of the flowing single cells and particles in the microchannel.In the first work of this dissertation, a microfluidic device that is able to simultaneously characterize the deformability and electrical impedance of individual biological cells in a high throughput manner (>1000 cells/min) has been developed. The combination of mechanical and electrical properties serves as a unique set of intrinsic cellular biomarkers for single-cell analysis, providing better differentiation of cellular phenotypes, which are not easily discernible via single-marker analysis. In the second work, a differential multiconstriction microfluidic device with 3D electrodes has been developed for high-ii throughput biophysical phenotyping at the single-cell level, referring to the simultaneous characterization of deformability (i.e., total transit time), electrical impedance and relaxation index of single cells. Compared with previously reported impedance-based microfluidic device for the measurement of electrical and mechanical properties of single cells, the employment of multiconstriction channels instead of single constriction enables the evaluation of relaxation index of single cells and the method developed for the creation of self-aligned 3D electrodes greatly reduces the complexity of device fabrication. In the third work of this dissertation, a novel microfluidic impedance cytometry device with N-shaped electrodes has been developed not only for the most accurate lateral position measurement of single cells and particles at the highest flow rate as compared to existing impedance-based methods but also can be used to characterize biophysical properties of cells simultaneously.These developed systems provide great potential for high-throughput and label-free biophysical phenotyping of single cells and thus may be used as a diagnostic tool for certain diseases (e.g., cancer, malaria and diabetes mellitus) associated with biophysical properties changes. Furthermore, integrating our microfluidic impedance flow cytometries with sorting techniques is a promising method to sort the cells with desired biophysical phenotyping for the biological and biomedical research and applications in a label-free manner. The efficiency of these sorting systems may be effectively evaluated by our novel microfluidic impedance cytometry with N-shaped electrodes.