Date of Award
Doctor of Philosophy (PhD)
The sorting of targeted cells or particles from a sample is a crucial step in the sample preparation process used in medical diagnosis, environmental monitoring, bio-analysis and personalized medicine. Current cell sorting techniques can be broadly classified as label based or label-free. Label-based techniques mostly rely on fluorophores or magnetic nanoparticles functionalized to bind with targeted cells. Although highly specific, this approach can be expensive and suffers from limitations in the availability of suitable markers. Label-free techniques exploit properties inherent to the cell, such as density and size, to simplify the sorting protocol and reduce cost by eliminating the need to incubate samples with labels. However, the specificity of separation is low due to minor differences between the density and size of many cells of interest. In this work, the use of dielectrophoresis (DEP) is emphasized as a label-free technique that exploits the combination of size and membrane capacitance of a cell as a marker. DEP is the movement of dielectric particles in the presence of a non-uniform electric field, which can be towards the electrode (positive DEP) or away from electrode (negative). The cell membrane capacitance used in this project can distinguish between cells based on their type, age, fate, and circadian rhythm to provide higher specificity than other label free sorting techniques. DEP has been demonstrated to separate various bio particles including viruses, plant and animal cells, biomolecules as well as stem cells. The work presented here integrates fabrication, numerical simulations, analysis and experimentation to focus on three main objectives 1) addressing the gaps of knowledge in electrode fabrication 2) developing analytical system for rapid cell sorting of cell population 3) demonstrating feasibility of automated single cell sorting. These are addressed in the following paragraphs in that order.
Carbon electrodes are excellent alternatives for DEP because of the ease of fabrication of 3D electrode geometries and low voltages involved. Previous works have used these electrodes for applications like DEP, electrochemical bio sensing applications, fuel cells and micro-capacitors. The fabrication process involves photo patterning of SU-8 posts followed by carbonization in an inert atmosphere. During pyrolysis, the structures retain their shape, but show shrinkage. Though the fabrication process is reproducible, limited knowledge is available about the shrinkage process. Shrinkage affects the design of devices where these structures are used because the electrode dimensions after pyrolysis vary from the design and resulting electric field in the domain is affected. Previous works observed dependence of shrinkage on structure height and width, but a defining relation between shrinkage and the geometry was lacking. In this work, shrinkage is studied as an effect of degassing through the lateral and top surface area of the electrodes. Empirical relations are to enable prediction of shrinkage in the design stage
StreamingDEP refers to focusing particles into narrow streams with a proper play of positive DEP and drag force. This is important in continuous sorting because of the high throughput, limited exposure of cells to electric field and ability of integration to further analysis steps. Though streamingDEP has been demonstrated previously, the dependence of the particle focusing on system parameters has not been studied. In this work, an analytical model is built to study the effect of electrode geometry, flow and electric field parameters as well as cell properties. The analytical expression developed here is validated by experiments and simulations.
Robotic transfer is required for efficient handling of cells and integration with analysis steps. Liquid handling robots are currently used in laboratories to transfer cells between different steps. Though they have precise control over the transfer of cells, the sorting ability is limited. To address these limitations, a proof-of-concept of roboticDEP device was innovated to enable transfer of targeted cells. The development of this system required studying the influence of DEP parameters in pick up and transfer of cells. The device was studied for elimination of contamination by using flow and electric field. The robotic DEP platform demonstrates a novel and unique approach to automated cell sorting with potential applications for single cell analysis, cell sorting and cell patterning.
Natu, Rucha, "Investigating the Use of Streaming and Robotic Dielectrophoresis to Enable Continuous Cell Sorting and Automatic Cell Transfer in Sample Preparation" (2018). All Dissertations. 2559.