Microfluidics

Sickle Cell Disease (SCD) is a genetic disease that affects approximately 100,000 people in the USA and millions worldwide. The disease is defined by a mutation in hemoglobin, the red blood cell’s oxygen carrying component. Under hypoxic (low oxygen) conditions, the mutated hemoglobin (known as HbS) polymerizes into rigid fibers that stretch the cell into a sickle shape. These rigid cells can occlude blood vessels and cause an individual immense pain. Currently, no point-of-care devices exist in the market for assisting those with SCD. Using microfluidics with custom designed portable impedance measuring hardware we can achieve label-free in vitro analyses of SCD rheology.
This dissertation presents two impedance-based devices for finger-prick volume blood testing, including a microflow cytometer for SCD diagnostics and a vaso-occlusion tester for monitoring blood flow activities. First, the microflow cytometer is validated by measuring the electrical impedance of individual cells flowing through a narrow microfluidic channel. Cellular impedance is interpreted by changes in subcellular components due to oxygen association-dissociation of hemoglobin, using an equivalent circuit model and Multiphysics simulation. Impedance values of sickle cells exhibit remarkable deviations from normal blood cells. Such deviation is quantified by a conformity score, which allows for measurement of SCD heterogeneity, and potentially disease severity. Findings from this study demonstrate the potential for SCD screening via electrical impedance. Second, a vaso-occlusion tester is validated by measuring the impedance response of blood flow within a microfluidic mimic of capillary bed.

The study of the electrical properties of red blood cells (RBCs) plays a crucial role in advancing our understanding of human health. As RBCs age, they undergo changes that affect hemorheology and blood microcirculation, which have far-reaching implications for disease research. Furthermore, the shortage of RBC storage units can be a major issue for patients, underscoring the importance of characterizing RBC aging with respect to cell densities. In individuals with abnormal hemoglobin disease, alterations in hemoglobin and its functionality can modify the volume and density of RBCs, making their study even more crucial. To this end, our aim is to investigate the impedance alterations of RBCs after distributing them into different layers based on their densities. We have developed a novel method for non-invasive, rapid, and real-time single-cell analysis of RBCs. Our approach involves the use of electrical impedance spectroscopy (EIS) to study the cells after performing cell fractionation. Our studies indicate an increasing trend for RBC resistance and a decreasing trend for the cell membrane as the density of the layer increases. Additionally, we have developed a method for extracting hemoglobin with high purity from fresh samples of RBCs. By passing lysed RBCs through ultrafiltration devices and removing debris and membranes, we were able to isolate hemoglobin. Using the EIS technique, we studied the alterations of impedance over a frequency range, obtaining valuable insight into the electrical properties of hemoglobin.

In recent years, point-of-care (POC) microfluidic platforms have transformed the healthcare landscape as they offer rapid, low-cost, and easy operational benefits. POC diagnostics play an important role in expediting the testing process in resource-constrained areas. These platforms have become a powerful tool as they offer comparable results with gold-standard methods. The gold standard methods require sophisticated lab locations and expensive equipment, to process the samples which is a significant challenge particularly for people living in low-income countries. To address these limitations, herein, in my dissertation, I have developed POC microfluidic platforms that can be operated outside the laboratory using lesser equipment statistically hence reducing the testing cost and time. The developed POC chips are used for infectious diseases diagnosis for viruses such as Zika, Hepatitis C Virus (HCV), and severe acute respiratory syndrome coronavirus 2 (SARSCoV-2). The entire virus detection process was executed inside a uniquely designed, inexpensive, disposable self-driven microfluidic chip with high sensitivity and specificity. In addition to this, I have also developed a microfluidic platform for functional sperm cell sorting from raw semen samples. The microfluidic chip offers a platform where the sperm cells experience different shear stress in different parts of the chip that facilitates isolation of competent sperm cells without impacting their integrity. Simultaneously, it also allows effortless collection of sorted sperm cells from the collection chamber which holds clinical significance. All things considered, the developed devices are inexpensive, disposable, easy-to-use, and rapid that provide results within one hour.

Among various sources for biofuels, microalgae provide at least three-orders-of-magnitude higher production rate of biodiesel at a given land area than conventional crop-based methods. However, microalgal biodiesel still suffers from significantly lower harvesting efficiency, making such a fuel less competitive. To increase the separation efficiency of microalgae from cultivation solution, an orbital microchannel was utilized that enabled the isolation of biofuel-algae particles from the effluent. The results obtained showed that the separation efficiency in the microfluidic centrifugal separator can be as high as 76% within a quick separation time of 30 seconds. Multiple parameters of algae behaviors and separation techniques such as initial concentration, pH and temperature were studied and manipulated to achieve better efficiencies. It was found that changing these factors altered the separation efficiency by increasing or decreasing flocculation, or “clumping” of the microalgae within the microchannels. The results suggested that an acidic condition would enhance the separation efficiency since in a basic environment, large flocs of microalgae would block and hinder the separation process. Furthermore, a hot temperature solution (around 33 °C) yielded to a higher separation efficiency. The important characteristics of the separator geometry and the infusion rate on algae separation were also very effective in the separation process. This study revealed that there is an opportunity to improve the currently low efficiency of algae separation in centrifugal systems using much smaller designs in size, ensuring a much more efficient algae harvesting.

The purpose of this research is to explore and investigate the biophysical properties of living cells using microfluidics based electrical impedance sensing (EIS) technique. It provides a non-invasive approach to detect label-free biological markers in the regulation of cellular activities even at a molecular level. We specifically focus on the development, testing, and theoretical modeling of electrical impedance spectroscopy for neuroblastoma cells and endothelial cells. First, we demonstrate that the EIS technique can be used to monitor the progressive mitochondrial fission/fusion modification in genetically modified human neuroblastoma cell lines. Our results characterize quantitatively the abnormal mitochondrial dynamics through the variations in cytoplasm conductivity. Secondly, we employ a real time EIS method to determine the biophysical properties of the junctions which join one endothelial cell with one another in a monolayer of endothelial cells. In particular, we examine the role of the protein, c-MYC oncogene, in the barrier function. Our results show that the downregulation of c-MYC oncogene enhances the endothelial barrier dysfunction associated with inflammation. Finally, we measure and find that the electrical admittance (the reciprocal of the impedance) of the monolayer of endothelial cellular networks exhibits an anomalous power law of the form, Y ∝ ωα, over a wide range of frequency, with the value of the exponent, α, depending on the severity of the inflammation. We attribute the power law to the changes of the intercellular electric permeability between neighboring endothelial cells. Thus, the inflammation gives rise to relatively smaller values of α compared to that of the no-inflammation group. Furthermore, we propose a simple percolation model of a large R-C network to confirm the emergent of power law scaling behavior of the complex admittance, suggesting that the endothelial network behaves as a complex microstructural network and its electrical properties may be simulated by a large R-C network.

Electrical impedance of cells is a sensitive indicator of changes in cellular structure and biophysical characteristics. Integration of electrical impedance sensing in microfluidics can be a useful tool for characterization of blood cells for their disease state, such as sickle cell disease and malaria. The first part of this dissertation presents application of a microfluidics-based electrical impedance sensor for the study of sickle cell disease. Dynamic cell sickling-unsickling process of blood cells in response to cyclic hypoxia was measured. Strong correlation was found between the electrical impedance data and patients’ hematological parameters such as levels of sickle hemoglobin and fetal hemoglobin. In addition, application of electrical impedance spectroscopy in narrow microfluidic channel was used for label-free flow cytometry and non-invasive assay of single sickle cells under controlled oxygen level. We demonstrate the capability of this new technique in differentiating normal red blood cells from sickle cells, as well as sickled cells from unsickled cells, using normoxic and hypoxic conditions. The second part of this dissertation reports an application of electrical impedance sensing for the study of placental malaria. Testing conditions were optimized so that electrical impedance can be used for real time monitoring of different cellular and molecular level variations in this in vitro model of placental malaria. Impedance characteristics of cell proliferation, syncytial fusion and long-term response of BeWo cells to adhesion of infected erythrocytes were obtained and related to the immunostaining results and inflammatory cytokines measurements. Comparing to the conventional optical microscope-based methods, electrical impedance sensing technique can provide a label-free, real-time monitoring tool to study erythrocytes and cytoadhesion, and can further be extended to other disease models and cell types.

Carbon capture and sequestration (CCS) has been considered a promising technology for mitigating heavy atmospheric carbon dioxide (CO2) concentration as an immediate response to global climate change and ocean acidification. Despite various previous studies on CCS, there has been a paucity of research to overcome many of the challenges. In geological carbon sequestration, there are two major issues in achieving a feasible means of storing CO2. The first is the slow reaction of carbonic acid (H2CO3) formation from the reaction between injected CO2 and brine. Another technical challenge to the realization of industrial-scale carbon sequestration is the drying-out of brine induced by CO2 advection. The resident brine near a wellbore area is rapidly evaporated while precipitating significant amounts of salt at pores when gaseous CO2 is continuously injected into these aquifers. On the other hand, in industrial post-carbon capture processes, monoethanolamine (MEA) has been dominantly used as an absorption solvent. However, it generates significant amounts of toxic wastewater containing chemicals difficult to treat. The objectives of this thesis are to address these challenges in CCS, making the CCS technology feasible and competitive. An innovative method for geologic carbon sequestration, namely nickel nanoparticles (Ni NPs) addition to the injection fluid was developed and evaluated, to address issues of the slow reaction in deep saline aquifers. The catalytic activity of Ni NPs was evaluated using the microfluidic technique to confirm their possibility of additive for enhancing CO2 hydration in deep saline aquifers. First of all, to achieve acceleration of CO2 dissolution under reservoir-specific conditions, the catalytic effect of Ni NPs was investigated by monitoring change in CO2 bubble size at various Ni NPs concentration, pH, and different levels of salinity. Then, steric stabilization of Ni NPs by adsorbing polymers has been studied to further enhance Ni NPs’ catalytic activity. Second, to overcome the brine drying-out challenge, a new strategy of sequential water injection with CO2 was proposed. This sequential injection strategy showed great potential for preventing aquifer formation damage by decreasing brine drying-out and enhancing CO2 dissolution significantly. Lastly, the CO2 capturing performance of Ni NPs as a possible additive in an MEA solvent was evaluated to meet CO2 reduction and environmental protection demands. The results were promising: the catalytic potential of Ni NPs accelerates the average CO2 absorption rate by 34% and 54% in the limited mixing and the high mixing conditions, respectively. The results presented in this dissertation could help alleviate global concerns raised by CCS technology and would offer strategies for stable CCS technology with improved efficiency.

Droplet microfluidics generates and manipulates microdroplets in microfluidic devices at high manufacturing efficiency and controllability. Microdroplets have proven effective in biomedical applications such as single-cell analysis, DNA sequencing, protein partitioning and drug delivery. Conventionally, a series of aqueous microdroplets containing biosamples is generated and controlled in an oil environment. One of the critical challenges in this system is that recovery of the aqueous samples from the oil phase is very difficult and often requires expensive and cumbersome post-processing. Also, the low Reynolds (Re) number characteristic of this system results in low throughput of droplet generation. To circumvent challenges and fully utilize microdroplets for practical clinical applications, this research aims to unpack the fundamental physics that governs droplet generation in oil-free systems including an aqueous two-phase system (ATPS) and a high inertial liquid-gas system.

In order for microfluidics devices to be marketable, they must be inexpensive and easy to use. Two projects were pursued in this study for this purpose. The first was the design of a chip alignment system for visual feedback, in which a two-layer microfluidic chip was placed under a camera and an image processing and linear algebra program aligned a computer model to it. The system then translated the new locations of air valves and could detect valve activation in a chip filled with food coloring. The second was the design of a cheap, portable system to detect phosphorus in water. This system could not be completed due to time constraints, but the methods were detailed, and design ideas were laid out for future work.