1,720,977 research outputs found
Development of Functional Material Scaffolds for Sensing Applications
Get PDFDevelopments in the field of chemical and biological sensors call for sensitive and selective sensing surfaces to provide consistent information about target analytes. Since such sensors are mostly operating in complex multi-component environments, their interaction with interferent can have deleterious effects on their activity. Thus, stable sensing surfaces form the most critical aspect of a biosensor design and their development requires reliable surface morphology and chemistry for allocation of chemical and bio-recognition elements.
Studies in this dissertation were aimed at developing modified titanium dioxide nanoparticles using techniques such as silanization and cross-linking to act as scaffolds for stable immobilization of proteins via direct covalent bonding or encapsulation in silica particles during its bio-inspired lysozyme mediation. Spatially defined presence of protein-reporter agents, on transparent titania nanoparticles coated on glass slides, enabled the development of fluorimetric array biosensors for simultaneous detection of multiple analytes. The different approaches used to develop the functional layers were compared in terms of biosensor sensitivity and stability.
Organophosphorus hydrolase (OPH) was used as the model biosensing enzyme to show the potential application of the above chemistries for the detection of organophosphate (OP) neurotoxins. Reporter pH responsive fluorophores conjugated to enzyme transduced the catalytic hydrolysis of OPs by OPH, into a measurable optical signal. The developed sensor has potential applications for the detection of OP pesticides in environmental samples. As an extension to OP detection, the principle of molecular recognition based on thermodynamic-complex formation of fluoride ions with aluminum(III) octaethylporphyrin contained in a plasticized film with chromoionophore was exploited for the detection of organophosphofluoridates like Diisopropyl Fluorophosphate (structural analogue of Sarin and Soman chemical nerve agents).
Studies also included the activation of magnesium silicate (florisil) particles with reactive chemicals for the development chemical sensors. Modified Nash reagent was utilized in the form of fluoral-P and adsorbed onto florisil micro-particles. These pre-activated particles were attached to the glass slide surface via tape and via dispersion in polydimethyl siloxane (PDMS) matrix. Fluorimetric quantification of photoluminescent product of formaldehyde and fluoral-P activated florisil, namely, 3,5-diacetyl-1,4-dihydrolutidine (DDL) allowed for the detection of formaldehyde
Electrochemical Sensors for the Detection of Tricresyl Phosphate and Determination of Acid Content in Engine Oils
Get PDFElectrochemical sensors were developed in this study for the detection of tricresyl phosphate (TCP), a toxic chemical found in airline cabins and determination of acid accumulation in engine oils upon extended usage.
A hydrolyzing column was developed that hydrolyzed TCP to electro-active cresols which were detected using a copper-nanoparticle-multi-walled carbon nanotubes modified glassy carbon electrode. The problem arised due to electrode fouling was solved using Sodium 3,5 dibromo-4-nitroso benzene sulfonate (DBNBS) reagent. An automated sensor was developed using LabVIEW® by integrating the hydrolyzing column, modified electrodes and potentiostat for on-site detection of TCP in airline cabins.
With extended usage, engine oil accumulates several acids by incomplete oxidation which increases the acid content of the oil. Iridium oxide coated titanium electrodes were fabricated to determine the increased acid content in artificially aged oils whose trend was in accordance with the Total Acid Number (TAN) values found by potentiometric titration. The pH sensing properties of iridium oxide were exploited for the detection of paraoxon, a toxic organophosphorus compound. An enzyme immobilized multi-channel pH sensing block was fabricated for its detection
Development of Functional Interfaces for Sensing Applications
Get PDFAn electrochemical device has been developed for the detection of gaseous tricresyl phosphate (TCP). Monitoring of neurotoxic TCP is important since it has been widely used as an additive in commercial jet engine oils, acting as a flame retardant and plasticizer. The process of air recirculation in most aircrafts could allow TCP to enter the cabin, if oil leakage occurs, and potentially harm the health and safety of the crew and passengers. Although a few of the new airplanes have begun to use a different air recirculation system which can reduce the possibility of TCP contamination, it is still a big issue for most airplanes that are currently in service throughout the world.
Since TCP has low saturated vapor pressure, a gaseous sample is not readily available and a special procedure was developed in our laboratory for conducting experiments. A TCP methanol solution was heated while N2 was bubbled though a flow system to vaporize the TCP. Since TCP is not electro-active and cannot be detected with electrochemical approaches, it was hydrolyzed to cresol using a special hydrolysis column in the flow system. Both of these operations were also performed with an automatic sampling device that was built in our lab. The presence of TCP in the hydrolysate samples of TCP, as well as real TCP-contained engine oils, was successfully detected by the electrochemical device within the linear range of 30-300 ppb of TCP in gas phase.
However, the electrochemical detection procedure results in oxidative polymerization of cresol on the electrode surface and this significantly distorts the results of measurements. A functional interface of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) composites has been introduced on the electrode surface to prevent electrode fouling. With this modified electrode, a similar linear range was obtained. More importantly, the modified electrochemical device was able to continuously detect gaseous TCP and has reliable responses over a longer period of time than with unmodified electrodes.
Electrode fouling is a common problem during the electrochemical analysis of phenolic compounds. A potential-drop-based model has been created in order to better understand the mechanism of electrode fouling, and it was able to quantitatively predict the electrode fouling in terms of time, applied potential, and the concentration of cresol. In order to obtain this model, the current-potential relationship was studied, and the amount of potential drop across the fouling layer was measured with a copper deposition method. This scientific model was comparable with experimental results, and would be helpful for the development of anti-fouling strategies
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Novel Sensor for Rapid Detection of Blood Cell Types-Magnetostrictive Microcantilevers
Get PDFMicrocantilevers have been around since the development of atomic force microscopy. The main attraction of cantilevers results from the fact that they can transduce many different signal domains into mechanical signals. Microcantilevers have different operational modes, but the one presented in this thesis is the dynamic microcantilever. Dynamic mode involves oscillation of the microcantilever at its resonance frequency. The main attraction of dynamic microcantilevers is that their resonance frequency is directly related to the mass attached to the microcantilever. Whenever mass is added to the surface of a microcantilever, a shift of resonance frequency will result. By monitoring the resonance frequency shift, the amount of mass added to the microcantilever can be determined. This type of detection can be applied
in different fields including food science, environmental monitoring, and medical industries. Bacteria detection that usually takes up to a couple of days for identification can be analyzed within minutes using sensors like microcantilevers. Recently, more publications are focusing on employing microcantilevers as biosensors to detect anything from Salmonella in food to E-coli in water. The objective of this thesis is to fabricate magnetostrictive microcantilevers and demonstrate the capabilities and advantages by using them to detect blood types. By observing the resonance frequency shift of the magnetostrictive microcantilevers, A and B blood types can be distinguished. Also presented in this thesis is the development of magnetostrictive thin films by electrochemical deposition. The thin film process allows numerous sensors to be fabricated with sizes ranging into the microns. These sensors can be made into microcantilevers. The magnetostrictive microcantilevers presented here can be driven and sensed wirelessly and also have a higher quality-value (Q-value) than other microcantilevers. By observing shifts in its resonance frequency due to blood cell loading, there seems to be some potential in being able to distinguish between certain blood types
Coupled self-assembly and flow alignment of silver nanorods
Get PDFThe recent development of facile routes for the production of inorganic nanorods, nanowires, and nanowhiskers has resulted in an array of materials with intriguing optical, electronic, magnetic and structural properties. However, the production of functional materials from these nanoscale building blocks often requires aligning the nanorods on the micro- to macro- scales. The theoretical foundation for self-assembly of anisotropic rigid materials in solution dates back to Onsager (1949), but understanding the liquid crystalline phase behavior of nanorod dispersions is a nascent field formed by the intersection of nanotechnology, liquid crystalline science and colloid science. This thesis reports the liquid crystalline assembly and flow alignment of silver nanorods. The techniques demonstrated for achieving liquid crystalline phases and shear alignment can be extended to any high aspect ratio rigid nanomaterial. The isotropic to biphasic phase transition was determined by optical microscopy and the biphasic to liquid crystalline phase transition was determined by both differential scanning calorimetry and optical microscopy. Aligned films were prepared and studied by surface enhanced Raman spectroscopy (SERS) and scanning electron microscopy (SEM). This work represents a significant step forward in developing a fundamental understanding about the impacts of nanorod concentration on liquid crystalline phase behavior as well as the potential for liquid crystalline dispersions of nanorods to be processed in to highly aligned macroscale coatings, films and fibers
The Development of Real-time Polymerase Chain Reaction for the Detection of Campylobacter jejuni
Get PDFCampylobacter jejuni (and related species) has been recognized as the most common pathogen that causes human bacterial gastroenteritis worldwide. It is the major cause of food-borne illnesses in the developed countries. Undercook poultry has been reported associated with the outbreak of campylobacter infection in human. Additionally, it has a very low infective dose, which can be as low as few hundred viable cells. Because of its leading role in causing food-borne illness in human, it is of paramount importance to develop methods that can be used to detection and differentiate C. jejuni. Traditional detection methods for Campylobacter jejuni require the enrichment of the food samples to reach a high number of bacterial cells. Therefore a rapid, specific and sensitive detection methods needs to be developed.
In this study, two real-time PCR protocols have been developed to target the C. jejuni-specific HipO gene. The first one was a SYBR Green I based real time PCR. A primer set was designed from the conserved region of the benzoyglycine amidohydrolase (hippuricase) gene of C. jejuni. This assay had a detection limit of 10 CFU/ml, was also capable of differentiating C. jejuni from closely related species, such as C. coli by melting curve analysis in addition to the highly specific detection of C. jejuni.
The second was a dual labeled hydrolysis probe (TaqMan®). A different set of primers was designed from the conserved region of the HipO gene of C. jejuni. The specificity of the assay was then tested with several Campylobacter strain and other Gram-negative bacteria. The PCR protocol was highly specific and only DNA from C. jejuni strains were amplified. Quantitative detection were conducted after generating the standard curve with serially diluted DNA extracted from pure culture and was found to be linear over 9 log units, with a standard curve correlation coefficient of 0.998. The detection limit for the current assay is 4.6 colony forming unit (CFU) per milliliter in pure cultures. This real-time PCR was also been used to tested with inoculated retail samples, and the detection limit of the assay was 100 CFU per milliliter. This assay may reduce the time for detection of C. jejuni in retail broiler samples
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