Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Lab-on-CMOS Sensors and Real-time Imaging for Biological Cell Monitoring(2019) Senevirathna, Bathiya; Abshire, Pamela; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Monitoring biological cell growth and viability is essential for in vivo biomedical diagnosis and therapy, and in vitro studies of pharmaceutical efficacy and material toxicity. Conventional monitoring techniques involve the use of dyes and markers that can potentially introduce side effects into the cell culture and often function as end-point assays. This eliminates the opportunity to track fast changes and to determine temporal correlation between measurements. Particularly in drug screening applications, high-temporal resolution cell viability data could inform decisions on drug application protocols that could lead to better treatment outcomes. This work presents development of a lab-on-chip (LoC) sensor for real-time monitoring of biological cell viability and proliferation, to provide a comprehensive picture of the changes cells undergo during their lifecycle. The LoC sensor consists of a complementary metal-oxide-semiconductor (CMOS) chip that measures the cell-to-substrate coupling of adherent cells that are cultured directly on top. This technique is non-invasive, does not require biochemical labeling, and allows for automated and unsupervised cell monitoring. The CMOS capacitance sensor was designed to addresses the ubiquitous challenges of sensitivity, noise coupling, and dynamic range that affect existing sensors. The design includes on-chip digitization, serial data output, and programmable control logic in order to facilitate packaging requirements for biological experiments. Only a microcontroller is required for readout, making it suitable for applications outside the traditional laboratory setting. An imaging platform was developed to provide time-lapse images of the sensor surface, which allowed for concurrent visual and capacitance observation of the cells. Results showed the ability of the LoC sensor to detect single cell binding events and changes in cell morphology. The sensor was used in in vitro experiments to monitor chemotherapeutic agent potency on drug-resistant and drug-sensitive cancer cell lines. Concentrations higher than 5 μM elicited cytotoxic effects on both cell lines, while a dose of 1 μM allowed discrimination of the two cell types. The system demonstrates the use of real-time capacitance measurements as a proof-of-concept tool that has potential to hasten the drug development process.Item Fluorescence Correlation Spectroscopy Studies of DNA Binding to Catanionic Surfactant Vesicles(2010) Lioi, Sara Bethany; English, Douglas; DeShong, Philip; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Catanionic vesicles, made from mixtures of oppositely charged surfactants, have potential in drug delivery and gene therapy applications. Fluorescence correlation spectroscopy (FCS) was utilized to study the electrostatic binding of DNA molecules to vesicles made from cetyltrimethylammonium tosylate (CTAT) and sodium dodecylbenzenesulfonate (SDBS). FCS is employed to make sensitive measurements of bilayer adsorption and compare the adsorption of two single-stranded, dye-labeled DNA molecules of different lengths. Previous experimentation had shown that small organic fluorescent dyes bind to oppositely charged vesicles, thus positively charged CTAT-rich vesicles were used in the study of DNA binding. FCS was performed on samples with a constant DNA concentration and varying surfactant concentrations in order to construct binding isotherms for a 5mer ssDNA molecule and a 40mer ssDNA molecule. The binding constant determined for 40mer ssDNA (~ 106) was larger than the constant for 5mer ssDNA (~ 105), and binding constants for both lengths of DNA were larger than those previously determined for small organic molecule fluorescent dyes, which were on the order of 104. Additionally, 40mer ssDNA was found to probe the critical aggregation concentration, which is the lower limit at which vesicles can form in a surfactant mixture. Ordinarily it would be expected that very few vesicles would form at this surfactant concentration, however the autocorrelation curves indicate that the 40mer is bound only to vesicles. Salt studies were also done with the 40mer ssDNA to determine how the binding of cargo molecules to the exterior of the vesicle would be affected by physiological salt concentrations. Binding affinity of the 40mer ssDNA was reduced with increasing salt concentration; this was thought to be due to the tosylate ion, as it is hydrophobic and intercalates into the vesicle bilayer. Subsequent experiments using cetyltrimethylammonium bromide (CTAB) indicated that the counterion is not a factor in loss of binding affinity under normal saline conditions. Because these surfactant vesicles have been shown to have potential in both drug delivery and gene therapy, it is important that the binding of the cargo molecule be able to withstand normal saline conditions.