Matching Items (123)
Description
Single molecules in a tunnel junction can now be interrogated reliably using chemically-functionalized electrodes. Monitoring stochastic bonding fluctuations between a ligand bound to one electrode and its target bound to a second electrode ("tethered molecule-pair" configuration) gives insight into the nature of the intermolecular bonding at a single molecule-pair level, and defines the requirements for reproducible tunneling data. Importantly, at large tunnel gaps, there exists a regime for many molecules in which the tunneling is influenced more by the chemical identity of the molecules than by variability in the molecule-metal contact. Functionalizing a pair of electrodes with recognition reagents (the "free analyte" configuration) can generate a distinct tunneling signal when an analyte molecule is trapped in the gap. This opens up a new interface between chemistry and electronics with immediate implications for rapid sequencing of single DNA molecules.
ContributorsChang, Shuai (Author) / Lindsay, Stuart (Thesis advisor) / Ros, Robert (Committee member) / Zhang, Peiming (Committee member) / Tao, Nongjian (Committee member) / Shumway, John (Committee member) / Arizona State University (Publisher)
Created2012
Description
Air pollution is one of the biggest challenges people face today. It is closely related to people's health condition. The agencies set up standards to regulate the air pollution. However, many of the pollutants under the regulation level may still result in adverse health effect. On the other hand, it is not clear the exact mechanism of air pollutants and its health effect. So it is difficult for the health centers to advise people how to prevent the air pollutant related diseases. It is of vital importance for both the agencies and the health centers to have a better understanding of the air pollution. Based on these needs, it is crucial to establish mobile health sensors for personal exposure assessment. Here, two sensing principles are illustrated: the tuning fork platform and the colorimetric platform. Mobile devices based on these principles have been built. The detections of ozone, NOX, carbon monoxide and formaldehyde have been shown. An integrated device of nitrogen dioxide and carbon monoxide is introduced. Fan is used for sample delivery instead pump and valves to reduce the size, cost and power consumption. Finally, the future work is discussed.
ContributorsWang, Rui (Author) / Tao, Nongjian (Thesis advisor) / Forzani, Erica (Committee member) / Zhang, Yanchao (Committee member) / Karam, Lina (Committee member) / Arizona State University (Publisher)
Created2012
Description
Hydrogenases catalyze the interconversion of protons, electrons, and hydrogen according to the reaction: 2H+ + 2e- <-> H2 while using only earth abundant metals, namely nickel and iron for catalysis. The enzymatic turnover of Clostridium acetobutylicum [FeFe]-hydrogenase has been investigated through the use of electrochemical and scanning probe techniques. Scanning tunneling microscopy (STM) imaging revealed sub-monolayer surface coverage. Cyclic voltammetry yielded a catalytic, cathodic hydrogen production signal similar to that observed for a platinum electrode. From the direct observation of single enzymes and the macroscopic electrochemical measurements obtained from the same electrode, the apparent turnover frequency (TOF) per single enzyme molecule as a function of potential was determined. The TOF at 0.7 V vs. Ag/AgCl for the four SAMs yielded a decay constant for electronic coupling (β) through the SAM of ~ 0.82 Å -1, in excellent agreement with published values for similar SAMs. One mechanism used by plants to protect against damage is called nonphotochemical quenching (NPQ). Triggered by low pH in the thylakoid lumen, NPQ leads to conversion of excess excitation energy in the antenna system to heat before it can initiate production of harmful chemical species by photosynthetic reaction centers. Here a synthetic hexad molecule that functionally mimics the role of the antenna in NPQ is described. When the hexad is dissolved in an organic solvent, five zinc porphyrin antenna moieties absorb light, exchange excitation energy, and ultimately decay by normal photophysical processes. However, when acid is added, a pH-sensitive dye moiety is converted to a form that rapidly quenches the first excited singlet states of all five porphyrins, converting the excitation energy to heat and rendering the porphyrins kinetically incompetent to perform useful photochemistry. Charge transport was also studied in single-molecule junctions formed with a 1,7-pyrrolidine-substituted 3,4,9,10-Perylenetetracarboxylic diimide (PTCDI) molecule. A reduction in the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbitals energy gap due to the electronic properties of the substituents is seen when compared to an unsubstituted-PTCDI. The small HOMO-LUMO energy gap allows for switching between electron- and hole-dominated charge transport with a gate voltage, thus demonstrating a single-molecule ambipolar field effect transistor.
ContributorsMadden, Christopher (Author) / Moore, Thomas A. (Thesis advisor) / Jones, Anne (Committee member) / Tao, Nongjian (Committee member) / Arizona State University (Publisher)
Created2012
Description
CpG methylation is an essential requirement for the normal development of mammals, but aberrant changes in the methylation can lead to tumor progression and cancer. An in-depth understanding of this phenomenon can provide insights into the mechanism of gene repression. We present a study comparing methylated DNA and normal DNA wrt its persistence length and contour length. Although, previous experiments and studies show no difference between the physical properties of the two, the data collected and interpreted here gives a different picture to the methylation phenomena and its effect on gene silencing. The study was extended to the artificially reconstituted chromatin and its interactions with the methyl CpG binding proteins were also probed.
ContributorsKaur, Parminder (Author) / Lindsay, Stuart (Thesis advisor) / Ros, Robert (Committee member) / Tao, Nongjian (Committee member) / Vaiana, Sara (Committee member) / Beckenstein, Oliver (Committee member) / Arizona State University (Publisher)
Created2012
Description
Parental care provides many benefits to offspring. One widely realized benefit is enhanced regulation of offspring's thermal environment. The developmental thermal environment during development can be optimized behaviorally through nest site selection and brooding, and it can be further enhanced by physiological heat production. In fact, enhancement of the developmental thermal environment has been proposed as the initial driving force for the evolution of endothermy in bird and mammals. I used pythons (Squamata: Pythonidae) to expand existing knowledge of behavioral and physiological parental tactics used to regulate offspring thermal environment. I first demonstrated that brooding behavior in the Children's python (Antaresia childreni) is largely driven by internal mechanisms, similar to solitary birds, suggesting that the early evolution of the parent-offspring association was probably hormonally driven. Two species of python are known to be facultatively thermogenic (i.e., are endothermic during reproduction). I expand current knowledge of thermogenesis in Burmese pythons (Python molurus) by demonstrating that females use their own body temperature to modulate thermogenesis. Although pythons are commonly cited as thermogenic, the actual extent of thermogenesis within the family Pythonidae is unknown. Thus, I assessed the thermogenic capability of five previously unstudied species of python to aid in understanding phylogenetic, morphological, and distributional influences on thermogenesis in pythons. Results suggest that facultative thermogenesis is likely rare among pythons. To understand why it is rare, I used an artificial model to demonstrate that energetic costs to the female likely outweigh thermal benefits to the clutch in species that do not inhabit cooler latitudes or lack large energy reserves. In combination with other studies, these results show that facultative thermogenesis during brooding in pythons likely requires particular ecological and physiological factors for its evolution.
ContributorsBrashears, Jake (Author) / DeNardo, Dale (Thesis advisor) / Harrison, Jon (Committee member) / Deviche, Pierre (Committee member) / McGraw, Kevin (Committee member) / Smith, Andrew (Committee member) / Arizona State University (Publisher)
Created2012
Description
Self-maintenance behaviors, like preening in birds, can have important effects on fitness in many animals. Birds produce preen oil, which is a mixture of volatile and non-volatile compounds, that is spread through their feathers during grooming and influences feather integrity, waterproofing, and coloration. As urban areas grow and present conditions that may demand increased feather self-maintenance (e.g. due to soiling, pollution, elevated UV exposure due to natural habitat alterations), it is important to examine how preening and preen oil may be affected by this process. I assessed variation in preen oil composition in house finches (Haemorhous mexicanus) as a function of sex, urbanization, and plumage hue, a sexually selected indicator of male quality. Preen oil samples from birds captured at urban and rural sites were analyzed using gas chromatography-mass spectrometry. We detected 18 major peaks, which we tentatively identified as esters, and found that, although there were no sex or urban-rural differences in preen oil constituents, there was a significant interactive effect of sex and urbanization, with rural females and urban males having higher amounts of some components. This suggests that factors that vary with sex or urbanization, such as the timing of seasonal cycles, are affecting preen oil composition. There were no significant relationships between coloration and preen oil composition, suggesting that preen oil composition does not vary with male quality.
ContributorsBrooks, Ellen Elizabeth (Author) / McGraw, Kevin (Thesis director) / Liebig, Juergen (Committee member) / Weaver, Melinda (Committee member) / Barrett, The Honors College (Contributor) / School of Life Sciences (Contributor)
Created2015-05
Description
Is it possible to treat the mouth as a natural environment, and determine new methods to keep the microbiome in check? The need for biodiversity in health may suggest that every species carries out a specific function that is required to maintain equilibrium and homeostasis within the oral cavity. Furthermore, the relationship between the microbiome and its host is mutually beneficial because the host is providing microbes with an environment in which they can flourish and, in turn, keep their host healthy. Reviewing examples of larger scale environmental shifts could provide a window by which scientists can make hypotheses. Certain medications and healthcare treatments have been proven to cause xerostomia. This disorder is characterized by a dry mouth, and known to be associated with a change in the composition, and reduction, of saliva. Two case studies performed by Bardow et al, and Leal et al, tested and studied the relationships of certain medications and confirmed their side effects on the salivary glands [2,3]. Their results confirmed a relationship between specific medicines, and the correlating complaints of xerostomia. In addition, Vissink et al conducted case studies that helped to further identify how radiotherapy causes hyposalivation of the salivary glands [4]. Specifically patients that have been diagnosed with oral cancer, and are treated by radiotherapy, have been diagnosed with xerostomia. As stated prior, studies have shown that patients having an ecologically balanced and diverse microbiome tend to have healthier mouths. The oral cavity is like any biome, consisting of commensalism within itself and mutualism with its host. Due to the decreased salivary output, caused by xerostomia, increased parasitic bacteria build up within the oral cavity thus causing dental disease. Every human body contains a personalized microbiome that is essential to maintaining health but capable of eliciting disease. The Human Oral Microbiomics Database (HOMD) is a set of reference 16S rRNA gene sequences. These are then used to define individual human oral taxa. By conducting metagenomic experiments at the molecular and cellular level, scientists can identify and label micro species that inhabit the mouth during parasitic outbreaks or a shifting of the microbiome. Because the HOMD is incomplete, so is our ability to cure, or prevent, oral disease. The purpose of the thesis is to research what is known about xerostomia and its effects on the complex microbiome of the oral cavity. It is important that researchers determine whether this particular perspective is worth considering. In addition, the goal is to create novel experiments for treatment and prevention of dental diseases.
ContributorsHalcomb, Michael Jordan (Author) / Chen, Qiang (Thesis director) / Steele, Kelly (Committee member) / Barrett, The Honors College (Contributor) / College of Letters and Sciences (Contributor)
Created2015-05
Description
Testosterone (T) is a steroid hormone that affects behavior and reproductive traits (e.g. spermatogenesis and ornamentation) in vertebrates. In addition to long-term influences, T can rapidly increase in males following aggressive male-male encounters. Less is known how females directly influence male T and behavior, though research with humans suggests that sexually attractive females elicit a greater increase in male T and reproductive behavior than unattractive females. In birds, the influence of female attractiveness on male T and behavior is currently untested. We hypothesized that T and courtship behavior in male zebra finches would correlate with female attractiveness. We used red leg bands to make females "attractive" and green bands to make them "unattractive" (unbanded females were controls) as previous research suggests that zebra finches prefer red colors over green in mating contexts. We collected blood from males before and after "speed-dating" trials to measure changes in plasma T and analyzed male courtship behaviors from trial video recordings. The likelihood of plasma T increasing after a trial was significantly greater in males who were with red-banded females compared to control females, suggesting males may find them more attractive than green or control females. Additionally, independent of band color, males who exhibited greater T differences initiated courtship sooner and spent more time closest to females. However, courtship initiation and time spent near females were not correlated with band color. Overall, our results suggest that female attractiveness can influence male reproductive physiology, but the presence of a female may trigger male courtship behavior.
ContributorsBero-Buell, Brianna Danielle (Author) / McGraw, Kevin (Thesis director) / Deviche, Pierre (Committee member) / Ligon, Russell (Committee member) / Barrett, The Honors College (Contributor) / School of Life Sciences (Contributor)
Created2014-05
Description
The objectives of this review include a discussion of the West Nile Virus phylogeny, transmission history, how the virus functions in the body and how it is a threat to public health, and then discusses these items related to vaccine technology surrounding West Nile Virus. This will include past developments, current research in the field and what it may take to develop such a vaccine safe and economical for human usage.
ContributorsSlinker, Haleigh Renee (Author) / Chen, Qiang (Thesis director) / Huffman, Holly (Committee member) / Oberstein, Bruce (Committee member) / Barrett, The Honors College (Contributor) / School of Letters and Sciences (Contributor)
Created2013-05
Description
Historically, the study of cognition has focused on species-specific learning, memory, problem-solving and decision-making capabilities, and emphasis was placed on the few high-performing individuals who successfully completed cognitive tasks. Studies often deemed the success of a small fraction of individuals as suggestive of the cognitive capacity of the entire species. Recently though, interest in individual variation in cognitive ability within species has increased. This interest has emerged concomitantly with studies of variation in animal personalities (i.e. behavioral syndromes). Cognitive ability may be closely tied to personality because the mechanisms by which an individual perceives and uses environmental input (cognition) should influence how that individual consistently responds to various ecological demands (personality). However, empirical support for links between animal cognition and behavioral syndromes is currently lacking. I examined individual variation in cognition and personality in male veiled chameleons, Chamaeleo calyptratus. I considered three axes of personality (aggression, activity, and exploratory behavior) and cognition in a foraging context using visual cues − specifically, the ability to associate a color with a food reward. I found that aggression was positively correlated with the proportion of correct choices and number of consecutive correct choices. Also, one measure of exploration (the number of vines touched in a novel environment) was correlated negatively with the proportion of correct choices and positively with the number of consecutive incorrect decisions. My investigation suggests that more aggressive, less exploratory chameleons were more successful learners, and that there exists a shared pathway between these personality traits and cognitive ability.
ContributorsBruemmer, Sarah Adele (Author) / McGraw, Kevin (Thesis director) / Rutowski, Ronald (Committee member) / Ligon, Russell (Committee member) / Barrett, The Honors College (Contributor) / School of Human Evolution and Social Change (Contributor) / School of Life Sciences (Contributor)
Created2013-05