A. James Clark School of Engineering
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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item CONFINED PHOTOTHERMAL HEATING OF NANOPARTICLE DISPLAYED BIOMATERIALS(2021) Hastman, David A; Medintz, Igor L; Aranda-Espinoza, Helim; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Controlling the temperature of biological systems has long been utilized as a tool for regulating their subsequent biological activity. Recently, photothermal heating of gold nanoparticles (AuNPs) has emerged as an efficient and remote method to heat proximal biological materials. Moreover, this technique has tremendous potential for controlling biological systems at the subcellular level, as specific components within the system can be heated while the larger system remains unaffected. The small size, biocompatiblilty, and optical properties of AuNPs make them attractive nanoscale heat sources for controlling biological systems. While the utility of photothermal heating has significantly advanced through the optimization of AuNP size, shape, and composition, the choice of incident light source utilized has largely been unexplored. One of the more interesting excitation sources is a femtosecond (fs) pulsed laser, as the subsequent temperature increase lasts for only a few nanoseconds and is confined to the nanoscale. However, it is not yet clear how biological materials respond to these short-lived and ultra-confined nanoscale spaciotemporal temperature increases. In this dissertation, we utilize fs laser pulse excitation to locally heat biological materials displayed on the surface of AuNPs in order to understand the corresponding heating profiles and, in turn, interpret how this can be used to modulate biological activity. Due to its unique temperature sensitive hybridization properties, we exploit double-stranded deoxyribonucleic acid (dsDNA) as our prototypical biological material and demonstrate precise control over the rate of dsDNA denaturation by controlling the laser pulse radiant exposure, dsDNA melting temperature, bulk solution temperature, and the distance between the dsDNA and AuNP surface. The rate of dsDNA denaturation was well fit by a modified DNA dissociation equation from which a “sensed” temperature value could be obtained. Evaluating this sensed temperature in the context of the theoretical temperature profile revealed that the ultra-high temperatures near the AuNP surface play a significant role in denaturation. Additionally, we evaluate this technique as a potential means to enhance enzyme activity and report that enhancement is governed by the laser repetition rate, pulse width, and the enzyme’s inherent turnover number. Overall, we demonstrate that the confined and nanosecond duration temperature increase achievable around AuNPs with fs laser pulse excitation can be used to precisely control biological function and establish important design considerations for coupling this technique to more complex biological systems.Item A Microfluidic Programmable Array for Label-free Detection of Biomolecules(2011) Dykstra, Peter Hume; Ghodssi, Reza; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)One of the most promising ways to improve clinical diagnostic tools is to use microfluidic Lab-on-a-chip devices. Such devices can provide a dense array of fluidic components and sensors at the micro-scale which drastically reduce the necessary sample volumes and testing time. This dissertation develops a unique electrochemical sensor array in a microfluidic device for high-throughput, label-free detection of both DNA hybridization and protein adsorption experiments. The device consists of a patterned 3 x 3 grid of electrodes which can be individually addressed and microfluidic channels molded using the elastomer PDMS. The channels are bonded over the patterned electrodes on a silicon or glass substrate. The electrodes are designed to provide a row-column addressing format to reduce the number of contact pads required and to drastically reduce the complexity involved in scaling the device to include larger arrays. The device includes straight channels of 100 micron height which can be manually rotated to provide either horizontal or vertical fluid flow over the patterned sensors. To enhance the design of the arrayed device, a series of microvalves were integrated with the platform. This integrated system requires rounded microfluidic channels of 32 micron height and a second layer of channels which act as pneumatic valves to pinch off selected areas of the microfluidic channel. With the valves, the fluid flow direction can be controlled autonomously without moving the bonded PDMS layer. Changes to the mechanism of detection and diffusion properties of the system were examined after the integration of the microvalve network. Protein adhesion studies of three different proteins to three functionalized surfaces were performed. The electrochemical characterization data could be used to help identify adhesion properties for surface coatings used in biomedical devices or for passivating sensor surfaces. DNA hybridization experiments were performed and confirmed both arrayed and sensitive detection. Hybridization experiments performed in the valved device demonstrated an altered diffusion regime which directly affected the detection mechanism. On average, successful hybridization yielded a signal increase 8x higher than two separate control experiments. The detection limit of the sensor was calculated to be 8 nM.Item Microcantilever Biosensors with Chitosan for the Detection of Nucleic Acids and Dopamine(2007-05-07) Koev, Stephan; Ghodssi, Reza; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Microcantilever biosensors allow label-free detection of analytes within small sample volumes. They are, however, often limited in sensitivity or specificity due to the lack of proper bio-interface layers. This thesis presents the use of the biopolymer chitosan as a bio-interface material for microcantilevers with unique advantages. Sensors coated with chitosan were designed, fabricated, and functionalized to demonstrate two distinct applications: detection of DNA hybridization and detection of the neurotransmitter dopamine. The first demonstration resulted in signals from DNA hybridization that exceed by two orders of magnitude values previously published for sensors coated with SAM (self assembled monolayer) interface. The second application is the first reported demonstration of using microcantilevers for detection of the neurotransmitter dopamine, and it is enabled by chitosan's response to dopamine electrochemical oxidation. It was shown that this method can selectively detect dopamine from ascorbic acid, a chemical that interferes with dopamine detection in biological samples.