Browsing by Subject "Liquid Crystal"

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    DNA Nanotechnology: Developing and Analyzing a New Tool for Sensing Allergens
    (2016-06) Brumann Clemente, Ana Paula
    Allergens are a major problem especially concerning public health and economy. There are more than 150 foods that can initiate allergic reactions, these reactions can elicit a mild response or a dangerous life threatening condition and in some extreme cases death. Milk and milk ingredients are one of the 8 foods that are responsible for about 90% of all food related allergic reactions. Food containing undeclared allergens in the label are misbranded and adulterated, and in accordance with the FSMA law must be recalled. It is estimated that the food industry can spend up to $10 millions dollars in direct costs from a recall. It was hypothesized that aptamer-amphiphile, a synthesis product from ssDNA aptamer and a hydrocarbon tale, in conjunction with liquid-crystal could be used as a sensor for detection of -lactoglobulin, an allergenic whey protein. The sensor was based on the self-alignment properties of liquid crystals based on the environment that it is exposed and on the capabilities of DNA aptamers to specific binding to targets. Results of this work showed that the aptamer-amphiphile of choice, amphiphile synthesized without a spacer between the DNA head group and the hydrocabon tail, had a great affinity to target, Kd= 45 ± 1.68 nM. In addition to it, it was possible to demonstrate that the interaction of the aptamer-amphiphile with the target protein, -lactoglobulin, using the sensor assembly resulted in images that can be easily identified under the polarizing microscope, sensor exposed to the aptamer-amphiphile alone gave a black image, once the protein was introduced the image was bright. Furthermore, the sensor developed has a limit of detection of 18.4ng of -lactoglobulin. It was also able to selectively identify the target protein, since when aptamer-amphiphile supported on the sensor was exposed to a random protein the image did not change as it did with -lactoglobulin. In conclusion, this sensor developed proves the concept that aptamer-amphiphile and the liquid crystal can potentially be used as a sensor technique in food plants to detect allergens in food contact surfaces.
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    Investigating the orientational order in smectic liquid crystals.
    (2010-06) Wang, Shun
    This thesis is composed of two projects. The first one is the investigation of a reversed phase sequence, which subsequently leads to the discovery of a novel Smectic-C liquid crystal phase. The 10OHFBBB1M7 (10OHF) compound shows a reversed phase sequence with the SmC∗ d4 phase occurring at a higher temperature than the SmC∗ phase. This phase sequence is stabilized by moderate doping of 9OTBBB1M7 (C9) or 11OTBBB1M7 (C11). To further study this unique phase sequence, the mixtures of 10OHFBBB1M7 and its homologs have been characterized by optical techniques. In order to perform the resonant X-ray diffraction experiment, we have added C9 and C11 compounds to the binary mixtures and pure 10OHF. In two of the studied mixtures, a new smectic-C∗ liquid crystal phase with six-layer periodicity has been discovered. Upon cooling, the new phase appears between the SmC∗ #11; phase having a helical structure and the SmC∗d4 phase with four-layer periodicity. The SmC∗ d6 phase shows a distorted clock structure. Three theoretical models have predicted the existence of a six-layer phase. However, our experimental findings are not consistent with the theories. The second project involves the mixtures of liquid crystals with different shapes. The role of different interactions in stabilizing the antiferroelectric smectic liquid crystal phases have been a long-standing questions in the community. By mixing the antiferroelectric smectic liquid crystal with achiral liquid crystal molecules with rod and hockey-stick shapes, distinct different behaviors are obtained. In the case of the mixtures of chiral smectic liquid crystals with rod-like molecules, all the smectic-C∗ variant phases vanish with a small amount of doping. However, the hockey-stick molecule is much less destructive compared to the rod-like molecule. This suggests that the antiferroelectric smectic liquid crystal molecules may have a shape closer to a hockey-stick rather than a rod.