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Dissertations / Theses on the topic 'Colorimetric chemistry'
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1
Crenshaw, Erik Daniel. "Stimuli Responsive Colorimetric Elastomers via Thiol-yne Chemistry." University of Akron / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron1555580690422118.
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Bring, Torun. "Red Glass Coloration : a Colorimetric and Structural Study." Doctoral thesis, Stockholm : Oorganisk kemi, KTH Kemi, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4176.
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Zhang, Yunfei Ph D. Massachusetts Institute of Technology. "Development of stimulus-responsive polydiacetylene systems for molecular colorimetric detection." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/118284.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 110-116).
Direct and convenient detection of hazardous molecules in the environment, agriculture, and industry plays a critical role in humanity's health and safety. In order to achieve this goal, I have rationally designed polydiacetylene systems that possess unique optical properties such as color changing in the presence of external stimulus. These advanced polydiacetylene systems are conjugated with functional groups having specific targeting ability toward targeted hazardous molecules to build up a stimulus-responsive structure for molecular colorimetric detections. In the first part of the work, pyridine-2-aldoxime, capable of binding pesticide malathion, was conjugated with diacetylene monomer, followed by the conjugate polymerization under UV irradiation to form a stimulus-responsive system. The rapid, specific and sensitive colorimetric detection of malathion was demonstrated both in aqueous suspension and on solid support. Within seconds, the successful detection of malathion through color changes observed by the naked eye was accomplished, with a detection limit of mmol/L for liquid suspensions and nmol/cm 2 for solid membranes. Furthermore, density functional theory (DFT) calculations on this system before and after binding to malathion unveiled the mechanism of spectral change as the detection progressed. The second part of the work describes the conjugation of dipicolylamine to diacetylene and the polymerization of as-conjugated diacetylene. This polydiacetylene-dipicolylamine system has visible colorimetric response to lanthanide ions exposure within one minute, and this response is highly selective toward lanthanide ions evidenced by the absence of colorimetric response to the control metal ion Hg²⁺. Remarkably, through the color change observation by naked eye, the lanthanide ions (Gd³⁺ Ce³⁺ Er³⁺) detection limit was shown to be as low as [mu]mol/L in aqueous suspensions and nmol/cm2 on solid supports. In summary, two polydiacetylene systems were developed and demonstrated to be rapid, sensitive and selective sensors for the colorimetric detection of their target molecules. The mechanism of the colorimetric response elucidated by DFT calculations, which is beneficial for future molecular sensor design. These research results not only develop the efficient sensor systems for the detection of pesticide and lanthanide ions but also be valuable for the design of more advanced polydiacetylene sensors of varying target molecules in the future.
by Yunfei Zhang.
Ph. D.
4
Ghanty, Uday. "TOWARDS DEVELOPMENT OF A NONINVASIVE & COLORIMETRIC GLUCOSENSOR." University of Akron / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=akron1185825768.
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Thomas, Elizabeth Marie. "The Development of Colorimetric Assays to Determine the Identity and Frequency of Specific Nucleobases in DNA Oligomers." UKnowledge, 2016. http://uknowledge.uky.edu/chemistry_etds/64.
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Colorimetric methods combined with color-changing chemical probes are widely used as simple yet effective tools for identifying and quantifying a wide variety of molecules in solution. For nucleic acids (DNA and RNA), perhaps the most commonly used colorimetric probe is potassium permanganate, which can be used to identify single-stranded pyrimidines (thymine and cytosine) in polymers. Unfortunately, permanganate is not an effective probe for identifying purines (adenine and guanine), especially in the presence of the more reactive pyrimidines. Therefore, robust methods for discriminating between the purines remain elusive, thereby creating a barrier toward developing more complex colorimetric applications. In this dissertation, we demonstrate that chromophores such as permanganate and bicinchoninic acid (BCA) and copper, however, when combined with nucleobase-specific chemical cleavage reactions, can be a colorimetric probe for the identification and quantification of cytosines, adenines and/or guanines in single-stranded DNA oligomers, even in the presence of thymines. Furthermore, the reactions are stoichiometric, which allows for the quantification of cytosine, adenine and/or guanine frequency in these oligomers. The BCA/copper reagent detects the reducing sugar, 2-deoxyribose, resulting from the chemical cleavage of a given nucleotide’s N-glycosidic bond. Therefore, these colorimetric assays are effectively detecting abasic sites in DNA oligomers, which are known to occur in damaged DNA. Our analytic approach termed colorimetric identification of exposed nucleic acids (CIENA) combines the use of BCA/copper, permanganate, and diphenylamine chromophores along with digital image capture to identify and quantify each nucleobase within DNA. The digital image color properties are quantified in terms of the image’s hue, saturation, and lightness using the CIELAB color space and ΔE quantification of color. CIENA is a simple, low-cost tool that could be applicable in various types of nucleic acid analyses, such as the quantification of nucleobase composition and the identification of damaged DNA.
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Gulamussen, Noor Jehan. "Electrospun sorbents for solid phase extraction (SPE) and colorimetric detection of pesticides." Thesis, Rhodes University, 2014. http://hdl.handle.net/10962/d1013241.
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The thesis presents the evaluation of polysulfone sorbents for solid phase extraction (SPE) and the development of colorimetric probes for pesticides analysis in water. Through electrospraying and electrospinning techniques, different morphologies of sorbents (particles, beaded fibers and bead-free fibers) were fabricated. The sorbents were morphologically characterized by scanning electron microscopy. Adsorption capacities of sorbents were evaluated by conducting recoveries studies for model pesticides; atrazine, chlorpyrifos and DDT using batch and column SPE modes. Better recovery results were achieved by employing the batch mode of fibers, as values ranged from 98 to 105percent. Further sorbent evaluation was conducted using breakthrough experiments and static experiments. The breakthrough studies indicated that 1700 μL was the sample volume that could be percolated with no breakthrough of the analyte that correspond to a concentration of 150 mg/g of sorbent that can be extracted without any loss of analyte. From static studies, quantities of each model compound adsorbed into the fiber at the equilibrium time were evaluated. The adsorbed atrazine was 65, chlorpyrifos 250 and DDT 400 mg/g of sorbent. Kinetic studies suggested retention mechanism following pseudo first and second order model observed by high correlation coefficients (> 0. 96), demonstrating the fiber affinity to retain both polar and non-polar compounds opening a possibility to be used as sorbent for sample preparation of different classes of pesticides in water. For the second part of the study simple strategies for colorimetric sensing based on silver nanoparticles and polivinylpyrrolidone capped nanoparticles were developed, respectively for atrazine and chlorpyrifos detection. The limits of detection of the methods were 3.32 and 0.88 mg/L for atrazine and chlorpyrifos respectively. The applicability of the probe in real samples was demonstrated by the recoveries studies of tap water varying from 94 to 104 percent. The versatility of the probe was demonstrated by affording a simple, rapid and selective detection of atrazine and chlorpyrifos in the presence of other pesticides by direct analysis without employing any sample handling steps. Attempt to incorporate the probes in a solid support was achieved by using nylon 6 as solid support polymer proving to be fast and useful for on-site detection.
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Paudyal, Janak 9255967. "Carbon Nanotube- and Gold Nanoparticle-Based Materials For Electrochemical and Colorimetric Sensing Applications." FIU Digital Commons, 2016. http://digitalcommons.fiu.edu/etd/2996.
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Carbon nanotubes (CNTs) and gold nanoparticles (AuNPs) are widely used for sensing applications due to their distinctive electrical and optical properties, and we have explored the development of methods that enable the incorporation of these nanomaterials into new and improved sensing devices.
As a means for fabricating simple, low-cost and fast detection platforms for various applications, we have developed paper-based electrochemical detection platforms based on CNTs or platinum nanoparticle (PtNP)-CNT composite materials. We describe the use of a paper-based, low density, a three-dimensional thin film of interconnected CNTs as an electrode material. We studied the electrochemical properties of these paper-based CNT electrodes and demonstrated their use as an electrochemical sensor for the sensitive detection of guanine-based nucleotides. We further describe the functionalization of this paper-based electrode by fabricating a PtNP-SWCNT hybrid film via a vacuum filtration-based method. The interconnected PtNP structure formed on top of the CNT-coated paper was directly used as an electrocatalyst for methanol oxidation. Compared to paper-based PtNP-SWCNT hybrid films formed by electrochemical deposition, hybrid films formed by vacuum filtration showed a higher electrochemical surface area and enhanced electrocatalytic response to methanol oxidation.
We have also developed methods based around DNA-modified AuNPs, which offer an excellent colorimetric platform for target detection. The DNA density on the surface of modified AuNPs affects enzymatic activity, colloidal stability of AuNPs, the orientation of the probe DNA and its hybridization efficiency. The combination of all these factors ultimately dictates the reaction time and sensitivity of colorimetric assays. We demonstrate the use of DTT as a modulator to control DNA surface coverage on the surface of AuNPs. Using this DTT treatment and a novel probe for exonuclease III activity, we have developed a colorimetric assay based on DTT-treated, DNA-modified AuNPs that can achieve more sensitive and rapid detection of DNA and enzymes relative to existing sensor platforms.
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Egleton, James Edward. "Small molecule colorimetric and fluorescent probes for specific protein detection." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:0a1a1c80-8055-491a-920a-3e17f7919e93.
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This thesis describes the design, synthesis, analysis, mechanistic evaluation and optimisation of small molecule probes for the specific detection of proteins, focusing on the target protein human arylamine N-acetyltransferase type 1 (HUMAN(NAT1)) and its murine homologue, mouse arylamine N-acetyltransferase type 2 (MOUSE(NAT2)). The HUMAN(NAT1) gene is reported to be one of the most highly overexpressed genes in estrogen-receptor-positive (ER+) breast tumours, leading to its potential use as both a novel diagnostic biomarker and a novel therapeutic target for this disease. Chapter 1 reviews the literature on optical methods for the specific detection of a protein target, exploring strategies both based on biosensors and on chemical probes, before introducing the arylamine N-acetyltransferases as a family of enzymes. In Chapter 2, a family of naphthoquinone inhibitors of HUMAN(NAT1) are introduced, which undergo a colour change from red to blue upon binding specifically to the enzyme. The mechanism of this colour change, a proton transfer-mediated process, is discussed via the synthesis, pharmacological and colorimetric evaluation of close analogues of the hit compound lacking a key acidic sulfonamide-NH proton. During these studies, it was found that direct O-methylation of a sulfonamide is possible under certain conditions; such a reaction has not previously been reported. Furthermore, upon heating in polar solvents the O-methylated sulfonamide was observed to undergo rearrangement, and the mechanism of this process is investigated via NMR and kinetic studies. In Chapter 3, the design, synthesis and evaluation of HUMAN(NAT1) inhibitors with improved pharmacological and colorimetric profiles over the initial hit are described. From this optimisation, structure-activity relationships and an in silico model of interactions between the inhibitors and enzyme are evaluated. Testing of these compounds in cellular environments, however, exposes some limitations of this approach, notably the lack of sensitivity of the probes when dosed at low concentrations in cellular samples. In order to overcome this limitation, in Chapter 4 fluorescent analogues of the hit compound are designed and synthesised. Initial compounds developed in this series possess promising properties, but each compound generated suffers from either a low fluorescent intensity, lack of a pH-dependent switch in fluorescence or a low fluorescence excitation wavelength, which overlaps with those of tryptophan or tyrosine residues in proteins. Insights into the mechanism of molecular fluorescence and application of some simple quantum mechanical principles, however, lead to the design of a species which possesses all the required properties. The fluorescent emission intensity of this probe correlates linearly with [MOUSE(NAT2)] in E. coli cell extracts, and can quantify as little as 0.64% MOUSE(NAT2) in the samples; furthermore, the probe is capable of unambiguously detecting HUMAN(NAT1) within a cell extract from the ER+ breast cancer cell line ZR-75-1; future work on this probe may therefore enable its clinical use in improved early diagnosis of breast tumours. This study also represents, to the best of our knowledge, the first ever example of a small molecule, non-covalent probe capable of quantifying the concentration of a target protein in cellular extracts. In Chapter 5, the series of naphthoquinone probes is further optimised in order to study the roles of HUMAN(NAT1) in a cellular environment. Firstly, structure-activity relationships are utilised to design inhibitors with improved physical properties such as aqueous solubility and cell membrane permeability, in order to test the effect of HUMAN(NAT1) inhibitors in tumour cell models, which could have implications for the future use of a HUMAN(NAT1) inhibitor as a therapeutic agent in oncology. Secondly, the effect of the cofactor folic acid on the function and activity of HUMAN(NAT1) is explored. Finally, in Chapter 6, the conclusions of this study are outlined and a hypothesis as to how the concepts developed in this thesis might be applied to alternative, more ubiquitous biological targets is discussed, paving the way for future investigations.
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Liang, Pingping. "Gold Nanoparticle-Based Colorimetric Sensors for Detection of DNA and Small Molecules." FIU Digital Commons, 2016. http://digitalcommons.fiu.edu/etd/2595.
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Biosensors have proven to be a powerful tool for detecting diverse targets, such as proteins, DNA, and small molecules representing disease biomarkers, toxins, drugs and their metabolites, environmental pollutants, agrichemicals, and antibiotics with high sensitivity and specificity.
The major objective of the research described in this dissertation was to develop low cost, low sample volume, highly sensitive and specific AuNP-based colorimetric sensor platforms for the detection of DNA and small molecules. With this in mind, we propose an instrument-free approach in chapter three for the detection of NADH with a sensor constructed on a paper substrate, based on the target-induced inhibition of AuNP dissolution. The successful detection of this important molecule opens the door to numerous possibilities for dehydrogenase characterization, because NAD+/NADH are essential cofactors for more than 300 dehydrogenase enzymes. To further increase the sensitivity of our hybridization-based assay for DNA detection, we developed an enzyme-assisted target recycling (EATR) strategy in chapter four and have applied such an EATR-based colorimetric assay to detect single-nucleotide mismatches in a target DNA with DNA-functionalized AuNPs. This assay is based on the principle that nuclease enzymes recognize probe–target complexes, cleaving only the probe strand. This results in target release, enabling subsequent binding to and cleavage of another probe molecule. When the probe is conjugated onto AuNPs, complete cleavage from the AuNP surface produces a detectable signal in high ionic strength environments as the nanoparticles undergo aggregation. With such enzyme-assisted amplification, target detection can occur with a very low nM detection limit within 15 minutes. The extent of DNA loading on the AuNP surface plays an important role in the efficiency of DNA hybridization and aptamer-target assembly. Many studies have shown that high surface-coverage is associated with steric hindrance, electrostatic repulsive interactions and elevated surface salt concentration, whereas low surface-coverage can result in nonspecific binding of oligonucleotides to the particle surface. In chapter five, we investigated DNA surface coverage effects, and apply this optimization in conjunction with a highly-specific aptamer to develop a sensitive colorimetric sensor for rapid cocaine detection based on the inhibition of nuclease enzyme activity.
10
Shesham, Vaishnavi. "Assessing Diphenyl Polyenes as PH Sensitive Colorimetric Probes of Proton Gradients in Polymer Coatings." University of Dayton / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1620133505202436.
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Shaw, Tiana C. "Preparation of Derivatized Polyaniline for Biosensing Applications." DigitalCommons@Robert W. Woodruff Library, Atlanta University Center, 2016. http://digitalcommons.auctr.edu/cauetds/54.
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Conducting polymers have emerged as a promising material for optoelectronics and chemical sensing application. Polyaniline (PANI) is a conductive polymer which can be easily functionalized to be specific for various biomolecules and has ideal sensor characteristics. The protonation and deprotonation of the polyaniline’s backbone by derivatization can result in color and conductive change responses. This makes it ideal for the construction of a real time, naked eye sensor. Derivatized polyaniline has previously been reported as a colorimetric sensor in solution. We plan to create a more practical sensor by synthesizing hydroxyl functionalized polyaniline thin films. In this study, we designed a process to functionalize polyaniline and deposit it as a thin film on quartz or silicon substrate via a dip coating process. To demonstrate the use of derivatized PANI in biosensing applications, derivatized and underivatized PANI thin films were treated with solutions of L-aspartic (Asp) acid at concentrations ranging from 10-8 mM to 103 mM and monitored utilizing UV-Vis spectroscopy. We found that the derivatized thin films change from deep blue to green color upon addition of Asp solution and showed a decrease in the characteristic quinoid ring peak at 600nm and the appearance of a new polaron peak at 425nm. The underivatized PANI films showed no colorimetric response indicating the hydroxyl functionalized PANI films are a more ideal material for a biosensing and naked eye detection. The polyaniline derivative was characterized using FT-IR spectroscopy, 1H NMR spectroscopy, UV-VIS spectroscopy, and Scanning Electron Microscopy. Additionally, conductivity studies were utilized to explore the material’s effectiveness as an electronic sensor using a 4-point probe to measure resistance.
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Tancu, Yolanda. "Electrospun nanofibers as solid phase extraction sorbents and support for alkylphenols colorimetric probes." Thesis, Rhodes University, 2014. http://hdl.handle.net/10962/d1012997.
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The thesis reports on fabricating alternative solid phase extraction (SPE) sorbents and colorimetric probes based on electrospun nanofibers for alkylphenols (APs). Hydroxyl methylated styrene [poly(co-styrene-CH₃OH)] and 3-oxobutanoate styrene [poly(co-styrene-OCOCH₃COCH₃)] copolymers were synthesized and fabricated into sorbent materials by electro-spinning/spraying. The fabricated morphologies consisting of bead free fibers, beaded fibers and particles were evaluated as SPE sorbents using batch experiments. Electropun fibers proved to be better sorbents as they exhibited extraction efficiency that exceeded 95% compared to 60% for beaded fibers and 40% for particles. In view to reduce sample and solvent volumes, smooth fibers were packed into pipette tips as SPE devices that yielded quantitative recoveries of APs from spiked wastewater samples. Recoveries ranged from 70% to 125% with LOD of 0.008, 0.01 and 0.1 μg mL⁻¹ for 4-tert octylphenol (4-t-OP), 4-octylphenol (4-OP) and 4-nonylphenol (4-NP) respectively, when using high performance liquid chromatography-fluorescence detector (HPLC-FLD). Furthermore, amino functionalised polydiacetylene polymers (PDAs), citrate capped gold (AuNPs) and silver nanoparticles (AgNPs) were evaluated as colorimetric probes for visual detection of APs. In colloidal studies, AuNPs probe showed a colour change from wine red to green upon introduction of analyte. UV-vis spectroscopy revealed the shifting of the surface plasmon resonance (SPR) peak from 525 nm to 729 nm induced by aggregation of AuNPs. For AgNPs probe, a colour change was observed from yellowish green to brown. Transmission electron microscopy (TEM) studies showed growth of AgNPs. A presumed oxidation of the analyte, forming an absorbing compound at 279 nm in both AgNPs and PDAs probes was also observed. For PDAs probe the colour change was from purple to pink. Concentrations as low as 30 μg mL⁻¹ were detectable in all colloidal based probes. Further colorimetric investigations were conducted with electrospun AuNPs-nylon 6 fiber mat. A colour change from purplish red to navy blue at concentrations of 1000 μg mL⁻¹ was observed. Electrospun AgNPs –nylon 6 fiber mat did not show a distinct colour change. High resolution scanning electron microscopy (HRSEM) revealed the analyte inducing the assembly of AuNPs and AgNPs as they covered the surface of the nanofiber mat. Electrospun nanofibers are a platform for analysis and thus tuning their chemistry will lead to sensitive and selective methods
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Guntupalli, Bhargav. "Nanomaterial-Based Electrochemical and Colorimetric Sensors for On-Site Detection of Small-Molecule Targets." FIU Digital Commons, 2017. http://digitalcommons.fiu.edu/etd/3488.
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An ideal biosensor is a compact and in-expensive device that is able to readily and rapidly detects different types of analytes with high sensitivity and specificity. The affectability of a biosensing methodology is subject to the limit of nanomaterials to transduce the target binding process to an improved perceptible signal, while the selectivity is accomplished by considering the binding and specificity of certain moieties to their targets. Keeping these requirements in mind we have chosen nanomaterials such as carbon nanotubes (CNTs) and gold nanoparticles (AuNPs) that has catalytic properties combined with their size, shape and configuration dependent chemical and physical properties as essential precursors and signaling components for creation of biosensors with tremendous sensitivity. The primary goal of the research work described in this dissertation is to develop and evaluate novel methods to detect various analytes using nanomaterials, at the same time making an affordable architecture for point-of-care (POC) applications. We report here in chapter 3 a simple and new strategy for preparing disposable, paper-based, porous AuNP/M-SWCNT hybrid thin gold films with high conductivity, rapid electron transfer rates, and excellent electrocatalytic properties to achieve multiple analyte electrochemical detection with a resolution that greatly exceeds that of purchased flat gold slides. We further explored the use of nanomaterial-based paper films in more complex matrices to detect analytes such as NADH, which can act as a biomarker for certain cellular redox imbalances and disease conditions. Carbon nanotubes with their large activated surfaces and edge-plane sites (defects) that are ideal for performing NADH oxidation at low potentials without any help of redox mediators minimizing surface fouling in complex matrices is described in chapter 4. With an instrument-free approach in mind we further focused on a colorimetric platform using split cocaine aptamers and gold nanoparticles (AuNPs) to detect cocaine for on-site applications as described in chapter 5. In chapter 5, the split aptamer sequences were evaluated mainly on three basic criteria, the hybridization efficiency, specificity towards the analyte (cocaine), and the reaction time to observe a distinguishable color change from red to blue. The assay is an enzyme-assisted target recycling (EATR) strategy following the principle that nuclease enzyme recognizes probe–target complexes, cleaving only the probe strand releasing the target for recycling. We have also studied the effect of the number of binding domains with variable chain lengths on either side of the apurinic (AP) site. On the basis of our results, we finally shortlisted the sequence combination with maximum signal enhancement fold which is instrumental in development of colorimetric platform with faster, and specific reaction to observe a distinctive color change in the presence of cocaine.
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Wang, Ling. "Applications of Paper Microfluidic Systems in the Field Detection of Drugs of Abuse." FIU Digital Commons, 2017. http://digitalcommons.fiu.edu/etd/3381.
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Over the years, colorimetric reagents and immunology have been widely used in screening tests for illicit drugs; however, the test kits are not always convenient for field use and often require the user to mix and develop a specific set of reagents. In our project, we have been working on alternative platforms based on paper microfluidic devices (uPADs) for field testing. These devices utilize wax channels printed on paper to direct the analyte towards a specific set of chemical reagents. Using the procedure, we have developed a six-channel chip that adapts known colorimetric reagents targeting cocaine, opiates, amphetamines and ketamine for multiplex detection. For more sensitive and specific determinations than the colorimetric reagents, we have also developed a paper device that utilizes the interaction between gold nanoparticles and drug specific aptamers.
The µPADs using colorimetric reagent are designed as a six-channel multiplexed system. Sequences of different reagents applied to each channel to produce a series of reactions and the color changes appear at the end of each channel. The entire process takes less than five minutes. The adjusted reagents produce specific color changes for seized drugs on the paper microfluidic devices. Procedures have been developed for the detection of cocaine, ketamine, codeine, ephedrine, morphine, amphetamine, methamphetamine, and MDMA. These devices have been tested for sensitivity, specificity and stability against a variety of potential interferences and test conditions.
Gold nanoparticles (AuNPs)/ aptamers µPADs were developed to detect cocaine. The presence of cocaine cause the binding with aptamers, and the gold nanoparitcles produced a salt-indicated aggregations and gave a color change of AuNPs from red to black. The absence of cocaine allowed the aptamers freely to bind gold nanoparticles, and no color change occured. The device had a preliminary validation of sensitvity and specificity against a variety of potential interferences.
The use of paper microfluidic devices permits the development of rapid, inexpensive and easily operated tests for drug samples in the field. They present a safe and convenient presumptive tool that can be used in the field.
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Peters, Kelley L. "Development of Presumptive and Confirmatory Analytical Methods for the Simultaneous Detection of Multiple Improvised Explosives." FIU Digital Commons, 2014. http://digitalcommons.fiu.edu/etd/1659.
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In recent years, there has been a dramatic increase in the use of improvised explosive devices (IEDs) due to ease of synthesis and improved controls placed on commercial/military explosives. Commonly used materials for IED preparations include fertilizers and industrial chemicals containing oxidizers such as ClO3-, ClO4-, and NO3-, as well as other less stable compounds, such as peroxides. Due to these materials having a wide range of volatility, polarity, and composition, detection can be challenging, increasing the amount of time before any analytical information on the identity of the explosive can be determined. Therefore, this research project developed two analytical methods to aid in the rapid detection of multiple explosive compounds.
The use of microfluidic paper-based analytical devices (µPADs) allows for the development of inexpensive paper devices utilizing colorimetric reactions, which can perform five or more simultaneous analyses in approximately five minutes. Two devices were developed: one for the detection of inorganic explosives including ClO3-, ClO4-, NH4+, NO3-, and NO2-, and the second device detects high/organic explosives including RDX, TNT, urea nitrate, and peroxides. Limits of detection ranged from 0.4 µg – 20 µg of explosive residue with an analysis time of less than five minutes.
Development of a confirmatory method utilizing infusion electrochemical detection-electrospray ionization-time-of-flight mass spectrometry (EC-ESI-TOF MS) and 18-crown-6 ethers to produce guest/host complexes with inorganic ions has also been completed. Utilizing this method the inorganic ions present in many IEDs can be successfully detected as ion pairs, while still allowing for the detection of other high explosives1. Placing an electrochemical detector before the mass spectrometer permits the detection of hydrogen peroxide, an analyte normally difficult to detect through mass spectrometry. Limits of detection ranged from 0.06 ppm - 2 ppm with an analysis time of less than two minutes.
The development of these presumptive and confirmatory analytical methods permits the detection of a wide range of components present in IEDs. These methods decrease the amount of time required to relay information on the type of explosives present by simplifying the analysis process in the field and in a laboratory.
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Dai, Jianming. "Microwave-assisted extraction (MAE) of neem and the development of a colorimetric method for the determination of azadirachtin related limonoids (AZRL)." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0035/MQ64339.pdf.
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Gazda, Daniel Bryan. "Development of colorimetric solid Phase Extraction (C-SPE) for in-flight Monitoring of spacecraft Water Supplies." Washington, D.C. : Oak Ridge, Tenn. : United States. Dept. of Energy. Office of Science ; distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2004. http://www.osti.gov/servlets/purl/835309-K3fMzj/webviewable/.
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Muenyi, Clarisse Sornsay. "Cell Toxicology Study of RRR-Alpha-Tocopheryl Polyethylene Glycol 1000 Succinate (TPGS)." Digital Commons @ East Tennessee State University, 2005. https://dc.etsu.edu/etd/1037.
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This research focused on the cytotoxic properties of RRR-alpha-tocopheryl polyethylene glycol 1000 succinate (TPGS) in transformed and cancerous cell lines. We used RAW264.7 macrophage and prostate cancer (LNCaP) cell lines in this study. TPGS caused cell death and decreased cell viability in a dose and time dependent manner. Cell death was evaluated fluorimetrically by employing the nucleic acid-binding fluorophore; propidium iodide. A colorimetric 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT) assay was used to evaluate cell viability. Cell death can occur through necrosis or apoptosis. Our results suggested that TPGS triggered apoptotic cell death. Induction of apoptosis, as measured by caspase 3 enzymatic activity, was dependent upon the TPGS dose and incubation time. Caspase 8 was activated before caspase 9, suggesting the importance of the death receptor pathway in apoptosis. Our results indicated that TPGS cytotoxicity could also be due to one of its products of hydrolysis, alpha-tocopheryl succinate.
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Otten, Michael P. "Nitrogen in the Environment: Blue Copper Proteins Involved in Ammonia Oxidation and A Novel Smartphone-based Strategy for Colorimetric Water Quality Measurements." Bowling Green State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1467989136.
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Unser, Sarah A. "Improving the Sensitivity and Selectivity of Localized Surface Plasmon Resonance Biosensors Toward Novel Point-of-Care Diagnostics." University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1561997005551383.
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Saki, Neslihan. "Xanthene-based Artificial Enzymes And A Dimeric Calixpyrrole As A Chromogenic Chemosensor." Phd thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12605340/index.pdf.
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This thesis covers the combination of two seperate work accomplished during the throughout the study. In the first part of the study, xanthene based artificial enzymes were synthesized, and kinetic hydrolysis studies done.
Artificial enzyme design is an active field of supramolecular chemistry and metalloenzymes are attractive targets in such studies. Enzymatic catalysis is essentially a &lsquomultifuctional&rsquo
catalysis. As part of our work, we designed and synthesized three novel xanthene derivatives. All three model contain Zn(II) in their active sites. Using the model substrate p-nitrophenyl acetate, we showed that the bifunctional model is at least an order of magnitude more active in catalyzing the hydrolysis of the substrate. Compared to the uncatalyzed hydrolysis reaction of the p-nitrophenyl ester at pH 7.0, the bifunctional model complex showed a 5714-fold rate acceleration. The second part of the thesis involves the design of a dimeric calixpyrrole as a chromogenic chemosensor. Anions are involved in a large number of biological processes and there is an interest in developing molecular sensors for these charged species. The calixpyrroles are a class of old but new heterocalixarene analogues that show considerable promise in the area of anion sensing. In this work, we have designed, synthesized and characterized a calixpyrrole-dimer anion sensor for its anion binding strength. The dimer forms stable complexes with p-nitrophenolate ion. This formed complex is used as a colorimetric sensor by displacing the chromogenic anion with the addition of various anions. like fluoride and acetate. The receptor shows strong affinity and high selectivity for fluoride anion, and also show reasonable affinity toward acetate. Thus, effective optical sensing of biochemically relevant these anions is accomplished using the calixpyrrole dimer.
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Silva, Filho Edson Cavalcanti. "O polissacarideo natural celulose quimicamente modificado no uso da remoção de cations e termoquimica da interação na interface solido/liquido." [s.n.], 2008. http://repositorio.unicamp.br/jspui/handle/REPOSIP/250055.
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Orientador: Claudio AiroldiTese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica
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Resumo: Dentre agentes usados para clorar a celulose, o cloreto de tionila apresentou melhor resultado com grau de substituição 1,00 na hidroxila primária. Esse intermediário reagiu para incorporar as moléculas 1,2-etilenodiamina, 1,4-butilenodiamina, acetilacetona e 2- aminometilpiridina. Na reação com etilenodiamina foram otimizadas as condições de síntese variando a quantidade e os solventes água ou N-N¿-dimetilformamida, demonstrando que quanto menor o volume de solvente 10,0 cm, maior a incorporação. Na ausência de solvente a quantidade incorporada foi maior, com 3,03±0,01 mmol de grupos pendentes por grama de celulose. Com 1,4-butilenodiamina não houve sucesso na ausência de solvente, porém, com a quantidade mínima de solvente foi 0,66±0,04 mmol g. A acetilacetona não reagiu com a celulose clorada, mas apenas após ser modificada com etilenodiamina e 5,70±0,22 mmol de nitrogênio ficou pendente por grama de celulose, após a formação da base de Schiff em ligações cruzadas. A molécula 2-aminometilpiridina foi incorporada na ausência de solvente, conseguindo 0,10±0,01 mmol g. Esses materiais foram caracterizados e aplicados na remoção de metais divalentes em meio aquoso, com as capacidades de adsorção: a) etilenodiamina 1,32±0,07; 1,91±0,07; 1,08±0,04 e 1,31±0,02, b) etilenodiamina/acetilacetona 2,32±0,06; 1,85±0,02; 1,70±0,04 e 1,65±0,02, c) butilenodiamina 0,32±0,03; 0,29±0,01; 0,26±0,03 e 0,25±0,02 e d) 2-aminometilpiridina 0,100±0,012, 0,093±0,021, 0,074±0,011 e 0,071±0,004 mmol g, para cobre cobalto, níquel e zinco, respectivamente. Foram determinadas as interações cátion-centro básico através de titulação calorimétrica em meio heterogêneo com valores exotérmicos de entalpia. A espontaneidade das reações é expressa pelos valores negativos da energia livre de Gibbs. Com exceção do cobre na celulose modificada com etilenodiamina, do cobalto, níquel e zinco com a celulose modificada com a 2-aminometilpiridina, todos os outros valores de entropia foram positivos, havendo assim um favorecimento entrópico
Abstract: Among the agents used to chlorinate cellulose, thionyl chloride gave better results with a degree of substitution 1.00 on primary hydroxyl group. This intermediate reacted to incorporate the molecules 1,2-ethylenediamine, 1,4-butylenediamine, acetylacetone and 2- aminomethylpyridine. For the reaction with 1,2-ethylenediamine the synthetic conditions was optimized, by varying the amounts and the solvents water or N,N¿-dimethylformamide, demonstrating that the lower the volume of solvent 10 cm, the higher is the incorporation. The absence of solvent yielded the highest amount incorporated, 3.03±0.01 mmol of pendant groups per gram of cellulose. For 1,4-butylenediamine the reaction in absence of solvent failed, however, with a minimum amount of solvent, it gave 0.66±0.04 mmol g. Acetylacetone did not react directly with the chlorinated cellulose, but when the precursor was chemically modified with 1,2-ethylenediamine to give 5.70±0.22 mmol of pendant nitrogen atom per gram of cellulose, Schiff base formation with crosslinking bonds was observed. Aminemethylpyridine was incorporated in the absence of solvent to give 0.10±0.01 mmol g. These materials were characterized and applied for divalent cations removal in aqueous solution. The adsorption capacities gave for: a) 1,2-ethylenediamine 1.32±0.07; 1.91±0.07; 1.08±0.04 and 1.31±0.02, b) 1,2-ethylenediamine/acethylacetone 2.32±0.06; 1.85±0.02; 1.70±0.04 and 1.65±0.02, c) butylenediamine 0.32±0.03; 0.29±0.01; 0.26±0.03 and 0.25±0.02 and d) 2-aminemethylpyridine 0.100±0.012, 0.093±0.021, 0.074±0.011 and 0.071±0.004 mmol g, for copper, cobalt, nickel and zinc, respectively. The cation-basic center interactions determined through calorimetric titration in heterogeneous conditions gave exothermic values, with spontaneity of reactions through all negative free Gibbs energies. With the exception of copper with cellulose chemically modified with 1,2-ethylenediamine, cobalt, nickel and zinc with cellulose modified with 2- aminemethylpyridine, all entropy values were endothermic, to give a favorable entropic conditions
Doutorado
Quimica Inorganica
Doutor em Quimica
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James, Dean. "Cavity enhanced spectroscopies for small volume liquid analysis." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:0b47d4a1-7f21-4c80-a8d4-496ca1080d52.
Full textAbstract:
Cavity enhanced spectroscopies (CES) are currently amongst the most sensitive spectroscopic techniques available for probing gas-phase samples, however their application to the liquid-phase has been more limited. Sensitive analysis of submicrolitre liquid samples is highly desirable, as miniaturisation allows for the reaction and analysis of scarce or expensive reagents, produces less waste, and can increase the speed of separations and reactions, whilst having a small footprint and high throughput. Absorption spectroscopy is a particularly desirable technique due to its universal, label-free nature, however its application to small volume liquid samples is hampered by the associated short absorption pathlengths, which limit sensitivity. CES improve sensitivity by trapping light within a confined region, increasing the effective pathlength through the sample. Three distinct types of optical cavity were constructed and evaluated for the purposes of making optical absorption measurements on liquid samples. The first incorporated a high optical quality flow cell into a "macrocavity" formed from two dielectric mirrors separated by 51.3 cm. Cavity losses were minimised by positioning the flow cell at Brewster's angle to the optical axis, and the setup was used to perform a single-wavelength cavity ringdown spectroscopy experiment to detect and quantify nitrite within aqueous samples. The detection limit was determined to be 8.83 nM nitrite in an illuminated volume of only 74.6 nL. Scattering and reflective losses from the flow cell surfaces were found to be the largest barrier to increased sensitivity, leading us to focus on the integration of cavity mirrors within a microfluidic flow system in the work that followed. In the second set of experiments, cavity enhanced absorption spectroscopy (CEAS) measurements were performed on Thymol Blue using custom-made microfluidic chips with integrated cavity mirrors. Unfortunately, due to the plane-parallel configuration of the mirrors and the corresponding difficulty in sustaining stable cavity modes, the results were underwhelming, with a maximum cavity enhancement factor (CEF) of only 2.68. At this point, attention was focussed toward a more well-defined cavity geometry: open-access plano-concave microcavities. The microcavities consist of an array of micron-scale concave mirrors opposed by a planar mirror, with a pathlength that is tunable to sub-nanometer precision using piezoelectric actuators. In contrast to the other experimental setups described, themicrocavities allow for optical measurements to be performed in which we monitor the change of wavelength and/or amplitude of a single well-defined cavity mode in response to a liquid sample introduced between the mirrors. In the first microcavity experiment, we used 10 μm diameter mirrors with cavity lengths from 2.238 μm to 10.318 μm to demonstrate refractive index sensing in glucose solutions with a limit of detection of 3.5 x 10-4 RIU. The total volume of detection in our setup was 54 fL. Thus, at the limit of detection, the setup can detect the change of refractive index that results from the introduction of 900 zeptomoles (500,000 molecules) of glucose into the device. The microcavity sensor was then adapted to enable broadband absorption measurements of methylene blue via CEAS. By recording data simultaneously from multiple cavities of differing lengths, absorption data is obtained at a number of wavelengths. Using 10 μm diameter mirrors with cavity pathlengths from 476 nm to 728 nm, a limit of detection, expressed as minimum detectable absorption per unit pathlength, of 1.71 cm-1 was achieved within a volume of 580 attolitres, corresponding to less than 2000 molecules within the mode volume of the cavity. Finally, a new prototype was developed with improved cavity finesse, a much more intense and stable light source, and improved flow design. Using a single plano-concave microcavity within the array with a cavity pathlength of 839.7 nm, and 4 μm radius of curvature mirror, absorption measurements were performed on Methylene Blue. Analysis of this data indicated a CEF of around 9270, and a limit of detection based on the measured signal-to-noise ratio of 0.0146 cm-1. This corresponds to a minimum detectable concentration of 104 nM Methylene Blue, which given the mode volume of 219 aL, suggests a theoretical minimum detectable number of molecules of 14.
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Salinas, Soler Yolanda. "Functional hybrid materials for the optical recognition of nitroaromatic explosives involving supramolecular interactions." Doctoral thesis, Editorial Universitat Politècnica de València, 2013. http://hdl.handle.net/10251/31663.
Full textAbstract:
La presente tesis doctoral titulada ¿Materiales funcionales híbridos para el reconocimiento
óptico de explosivos nitroaromáticos mediante interacciones supramoleculares¿ se basa en la
combinación de principios de Química Supramolecular y de Ciencia de los Materiales para el
diseño y desarrollo de nuevos materiales híbridos orgánico-inorgánicos funcionales capaces de
detectar explosivos nitroaromáticos en disolución.
En primer lugar se realizó una búsqueda bibliográfica exhaustiva de todos los sensores
ópticos (cromogénicos y fluorogénicos) descritos en la bibliografía y que abarca el periodo
desde 1947 hasta 2011. Los resultados de la búsqueda están reflejados en el capítulo 2 de esta
tesis.
El primer material híbrido preparado está basado en la aplicación de la aproximación de los
canales iónicos y, para ello, emplea nanopartículas de sílice funcionalizadas con unidades
reactivas y unidades coordinantes (ver capítulo 3). Este soporte inorgánico se funcionaliza con
tioles (unidad reactiva) y una poliamina lineal (unidad coordinante) y se estudia el transporte
de una escuaridina (colorante) a la superficie de la nanopartícula en presencia de diferentes
explosivos. En ausencia de explosivos, la escuaridina (color azul y fluorescencia intensa) es
capaz de reaccionar con los tioles anclados en la superficie decolorando la disolución. En
presencia de explosivos nitroaromáticos se produce una inhibición de la reacción escuaridinatiol y la suspensión permanece azul. Esta inhibición es debida a la formación de complejos de
transferencia de carga entre las poliaminas y los explosivos nitroaromáticos.
En la segunda parte de esta tesis doctoral se han preparado materiales híbridos con
cavidades biomiméticas basados en el empleo de MCM-41 como soporte inorgánico
mesoporoso (ver capítulo 4). Para ello se ha procedido al anclaje de tres fluoróforos (pireno,
dansilo y fluoresceína) en el interior de los poros del soporte inorgánico y, posteriormente, se
ha hidrofobado el interior de material mediante la reacción de los silanoles superficiales con
1,1,1,3,3,3-hexametildisilazano. Mediante este procedimiento se consiguen cavidades
hidrófobas que tienen en su interior los fluoróforos. Estos materiales son fluorescentes cuando
se suspenden en acetonitrilo mientras que cuando se añaden explosivos nitroaromáticos a
estas suspensiones se observa una desactivación de la emisión muy marcada. Esta
desactivación de la emisión es debida a la inclusión de los explosivos nitroaromáticos en la
cavidad biomimética y a la interacción de estas moléculas (mediante interacciones de ¿-
stacking) con el fluoróforo. Una característica importante de estos materiales híbridos
sensores es que pueden ser reutilizados después de la extracción del explosivo de las
cavidades hidrofóbicas. En la última parte de esta tesis doctoral se han desarrollado materiales híbridos orgánicoinorgánicos funcionalizados con ¿puertas moleculares¿ que han sido empleados también para
detectar explosivos nitroaromáticos (ver capítulo 5). Para la preparación de estos materiales
también se ha empleado MCM-41 como soporte inorgánico. En primer lugar, los poros del
soporte inorgánico se cargan con un colorante/fluoróforo seleccionado. En una segunda etapa,
la superficie externa del material cargado se ha funcionalizado con ciertas moléculas con
carácter electrón dador (pireno y ciertos derivados del tetratiafulvaleno). Estas moléculas ricas
en electrones forman una monocapa muy densa (debida a las interacciones dipolo-dipolo
entre estas especies) alrededor de los poros que inhibe la liberación del colorante. En
presencia de explosivos nitroaromáticos se produce la ruptura de la monocapa, debido a
interacciones de ¿-stacking con las moléculas ricas en electrones, con la consecuencia de una
liberación del colorante atrapado en el interior de los poros observándose una respuesta
cromo-fluorogénicaSalinas Soler, Y. (2013). Functional hybrid materials for the optical recognition of nitroaromatic explosives involving supramolecular interactions [Tesis doctoral]. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/31663
Alfresco
Premiado
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Ojha, Yagya Raj. "Selection and Characterization of ssDNA Aptamers for Salivary Peptide Histatin 3 and Their Application Towards Assay and Point-of-Care Biosensing." University of Toledo / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1575992671104993.
Full text
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Wujcik, Evan K. "Discovery of Nanostructured Material Properties for Advanced Sensing Platforms." University of Akron / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1374414126.
Full text
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Phillips, Paige Gale. "Examining Activity Organization in Plazas through Geochemical Analysis at Tlalancaleca, Puebla, Mexico (800 BC-AD 100)." Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5434.
Full textAbstract:
This research aims to understand the organization of activities across a prehispanic urban center at the Formative period site of Tlalancaleca (800 BC- AD 100), located in Puebla, Mexico. This study analyzes soil samples at the central civic-ceremonial complex of Cerro Grande in an attempt to understand the use of space. This work is a part of the larger Proyecto Arqueológico Tlalancaleca, Puebla (PATP), which is focused on understanding the socio-political organization at Tlalancaleca that led to this site of early urbanism. Soil samples from Tlalancaleca are analyzed using three chemical methods to perform a cross-comparison of analytical methods. These three methods are inductively coupled plasma-optical emission spectrometry (ICP-OES), Mehlich 3 soil phosphorus colorimetry, and portable X-ray fluorescence (pXRF) spectrometry. The final results of this soil analysis confirm that the Cerro Grande Complex was an actively used space, with areas maintained for specific uses and areas where activities changed over time. In the comparison of methods, ICP-OES was found to be the most comprehensive, precise, and accurate method to use, while pXRF and Mehlich colorimetry were found to show differing information with regards to available and natural concentrations of the different elements. An analytical examination of phosphorus, strontium, calcium, and barium revealed evidence of construction of monumental buildings, a cache, and possible separate feasting areas, indicating that physical spaces and constructions were likely attached to social and political organizations.
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Santos, Figueroa Luis Enrique. "New approaches for the development of chromo-fluorogenic sensors for chemical species of biological, industrial and environmental interest." Doctoral thesis, Universitat Politècnica de València, 2015. http://hdl.handle.net/10251/43216.
Full textAbstract:
El presente proyecto de investigación está enfocado al desarrollo de sensores químicos fluoro-cromogénicos, para la detección y determinación de especies químicas de interés biológico, industrial y medioambiental de forma selectiva y con alta sensibilidad.
En forma general, se busca el diseñar nuevos sistemas sensores basados en compuestos (receptores) formados por dos unidades: una unidad coordinante que interacciona con el anión a determinar y una unidad generadora de señal que alerta del reconocimiento molecular efectuado.
Durante este estudio se están preparando diversas moléculas receptoras funcionalizandas con grupos modificadores de estructura para evaluar su influencia sobre las capacidades de detección y selectividad como receptores de especies específicas en diferentes condiciones y medios.
Las diferentes aproximaciones en prueba implican a su vez el diseño y síntesis molecular, así como el análisis de las diferentes señales ópticas producidas en el reconocimiento, con el fin de diseñar sistemas de alta eficacia y eficiencia, y con posibilidades reales de aplicación.Santos Figueroa, LE. (2014). New approaches for the development of chromo-fluorogenic sensors for chemical species of biological, industrial and environmental interest [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/43216
TESIS
Premiado
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Reddy, Anvesh. "Phosphorus Transport and Distribution in Kentucky Soils Prepared Using Various Biochar Types." TopSCHOLAR®, 2012. http://digitalcommons.wku.edu/theses/1210.
Full textAbstract:
Conserving the environment is an issue that is gaining popularity day by day. Phosphorus transfer from agricultural soils is an important environmental issue that is being closely observed as the transport of phosphorous to water bodies is adversely affecting water quality due to accelerated eutrophication. It is important to establish phosphorous models that accurately account for soil test phosphorous. Standard models like SWAT (Soil and Water Assessment Tool) and EPIC (Environmental Policy Integrated Climate) were designed for serving this purpose. They are now used as the basis for developing new models that can more accurately account for the phosphorus transport, depending on local soil conditions and external factors like climate, addition of biochar or other soil amendments. Our research involved development of new methods from published data that are applied to different soils from Kentucky that are incubated for various time periods, with and without the addition of biochar amendments. Changes in the soil labile phosphorus content after phosphorus addition to and depletion from these incubated soils was measured to discern the effect of biochar on the rates of phosphorus transport. The measured labile phosphorus was further analyzed using statistical analysis software drawing comparisons among treatments without biochar, with low temperature biochar and high temperature biochar for specific soil-biochar combinations. Loamy sand soils with both pine chips and switch grass biochar types have shown slightly increased leeching of phosphorus upon addition of biochar whereas clay loam soils have not shown any significant change upon addition of biochar.
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Zhang, Chen. "A colorimetric sensor array for aqueous analyses /." 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3250354.
Full textAbstract:
Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 2006.Source: Dissertation Abstracts International, Volume: 68-02, Section: B, page: 0944. Adviser: Kenneth S. Suslick. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.
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Bernstein, Alexis Ryan. "Discrimination of hemp and marijuana using a fieldable, combined, colorimetric/spectrophotometric approach." Thesis, 2020. https://hdl.handle.net/2144/42081.
Full textAbstract:
The passage of the 2018 Farm Bill, which included the legalization of regulated hemp production, is causing identification concerns within the forensic science community. Cannabis has two legal constructs, hemp and marijuana, which are macroscopically and microscopically indistinguishable. Hemp and marijuana both contain Δ9-tetrahydrocannabinol (THC), however, the difference between them is based on the percentage of THC by dry weight. Per Section 7606 of the Agricultural Act, hemp is defined as containing less than 0.3% THC by dry weight. This project aims to create a commercially available, off the shelf, fieldable test kit to discriminate between hemp and marijuana. To be able to discriminate between the two categories, it will be important to be able to quantitate the percentage of THC. Fast Blue BB salt (FBBBS) has been shown in previous studies to produce distinct color changes with cannabidiol (CBD) and THC. Eight hemp varieties were obtained, as well as five varieties of marijuana. Cannabinoids were extracted from the plant material with the use of acetonitrile. The colorimetric reaction with FBBBS uses sodium hydroxide as the catalyst. Following the reaction, the samples were analyzed using one of two spectrophotometers, a commercially available handheld device and the other a larger bench-top style spectrophotometer. Qualitative results to date indicate that FBBBS produces a different color change with hemp and marijuana. Hemp produces a dark orange, whereas marijuana produces a golden yellow. Additionally, Ultraviolet–Visible Spectroscopy results show that there are differences in the peak patterns between hemp and marijuana. There are commonalities of absorbances at particular wavelengths between different varieties of hemp, as well as the different varieties of marijuana. This study is to be further expanded on with some of the steps listed as Future Directions. Quantitative data has not yet been obtained, which is an important aspect of the field-test kit to differentiate between the two categories of cannabis. Furthermore, calibration curves will need to be created and used to quantitate the amount of THC and CBD present in purchased samples. A prototype kit has been constructed, consisting of a ruggedized Pelican™ case, a handheld visible spectrophotometer, a sample homogenizer, solvents, transfer pipettes and cuvettes. Another spectrophotometer will be obtained that scans a wider wavelength range.2021-08-19T00:00:00Z
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Carter, Rhiannon. "Characterization and colorimetric analysis of semi-synthetic Salvia divinorum analogues." Thesis, 2014. https://hdl.handle.net/2144/13308.
Full textAbstract:
Salvia divinorum is a hallucinogenic herb from the mint family, Lamiaceae. An estimated 1.8 million people over the age of 12 have used S. divinorum in their lifetime as of 2008. The abuse of S. divinorum is attractive to teens and young adults who wish to experiment with psychoactive materials. The plant material and extracts are widely available via the Internet, and it is known that S. divinorum will not show up on common drug screens.
The active component in S. divinorum is salvinorin A, which is a non-nitrogenous diterpene that is a highly selective kappa opioid receptor (KOR) agonist, reported to be the most potent naturally occurring hallucinogen. Since salvinorin A is such a selective and potent agonist of the KOR, there is interest in researching analogues in efforts to develop and understand therapeutic drugs for depression, schizophrenia, and other mental illnesses, resulting in the discovery of analogues with increased potency. These semi-synthetic salvinorin analogues have been abused by spraying the drug on innocuous plant material or on cigarette papers as a substrate for smoking. This practice poses a significant health risk, as most new analogues will have little safety and toxicity data associated with common abuse routes.
Chemical characterization of the potent analogue, salvinorin B ethoxymethyl ether (SB-EME) was performed in order to develop methods of differentiation from Salvia divinorum and salvinorin A. These characterization techniques include HPLC, UV/Vis, NMR, and a colorimetric assay with Ehrlich's reagent. Adulteration of other plant materials with salvinorin A and analogues was performed and analyzed to determine if fortified materials can be detected by colorimetric assay.
The validation studies of the HPLC method for SB-EME were found to be accurate (%RE < 12%), precise (RSD = 12%), and linear (R2 = 0.9993) over the mass range of 0.038 µg - 4.8 µg. The LOD was determined to be 0.038 µg, and the LOQ was determined to be 0.113 µg. Significant matrix effects were observed when using Salvia officinalis as a blank matrix, affecting the accuracy and selectivity of the method. However, the purified solutions of SB-EME had baseline resolution from salvinorin A and salvinorin B, which allows for easy qualitative distinction if adulterated samples are suspected.
UV/Vis analysis provided a rapid and facile SB-EME characterization method. The UV/Vis trace for SB-EME was distinguishable from both salvinorin A and salvinorin B. NMR analysis confirmed the structures of salvinorin A, salvinorin B and SB-EME, with resonances specific to each compound.
The colorimetric assay with Ehrlich's reagent provided a red-orange result with salvinorin B and SB-EME, similar to salvinorin A. While this does not provide differentiation in the field, it does allow all materials related to Salvia divinorum to be identified and collected for further analysis in the lab, as this colorimetric analysis allows easy distinction from common kitchen herbs such as mint, basil, and sage. Characterization of the colored species in the assay with Ehrlich's reagent was performed with UV/Vis, HPLC, and NMR. The UV/Vis analysis showed a new peak at 500 nm in the aqueous layer, which would correspond to a red-orange color. HPLC analysis revealed a new, highly retained peak from the DCM layer of the assay. 1H NMR analysis indicated that the backbone of the salvinorins was not stable in acid, and the molecule that creates the color was likely a degraded analogue.
The analysis of the adulterated plant materials by colorimetric assay was inconclusive, as color intensity decreased as concentration of spiked standard increased. HPLC analysis of the vial remnants after the colorimetric assay confirm recoveries of the spiking compounds up to an average of 22% for salvinorin A, 96% for salvinorin B, and 41% for SB-EME over all matrices, indicating incomplete deposition of standard material onto the plant material.
In conclusion, salvinorin B ethoxymethyl ether can be detected in the field through the use of Ehrlich's reagent as a colorimetric assay. Further laboratory tests, including HPLC and UV/Vis, were shown to easily distinguish the ether derivative from salvinorin A and B.
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"Novel Colorimetric Sensors with Extended Lifetime for Personal Exposure Monitoring." Doctoral diss., 2019. http://hdl.handle.net/2286/R.I.55643.
Full textAbstract:
abstract: Air pollution has been linked to various health problems but how different air pollutants and exposure levels contribute to those diseases remain largely unknown. Researchers have mainly relied on data from government air monitoring stations to study the health effects of air pollution exposure. The limited information provided by sparse stations has low spatial and temporal resolution, which is not able to represent the actual exposure of individuals. A tool that can accurately monitor personal exposure provides valuable data for epidemiologists to understand the relationship between air pollution and certain diseases. It also allows individuals to be aware of any ambient air quality issues and prevent air pollution exposure. To build such a tool, sensors with features of fast response, small size, long lifetime, high sensitivity, high selectivity, and multi-analyte sensing are of great importance.
In order to meet these requirements, three generations of novel colorimetric sensors have been developed. The first generation is mosaic colorimetric sensors based on tiny sensor blocks and by detecting absorbance change after each air sample injection, the target analyte concentration can be measured. The second generation is a gradient-based colorimetric sensor. Lateral transport of analytes across the colorimetric sensor surface creates a color gradient that shifts along the transport direction over time, and the sensor tracks the gradient shift and converts it into analyte concentration in real-time. The third generation is gradient-based colorimetric arrays fabricated by inkjet-printing method that integrates multiple sensors on a miniaturized sensor chip. Unlike traditional colorimetric sensors, such as detection tubes and optoelectronic nose, that are typically for one-time use, the presented three generations of colorimetric sensors aim to continuously monitor multiple air pollutants and the sensor lifetime and fabrication methods have been improved over each generation. Ozone, nitrogen dioxide, formaldehyde and carbon monoxide are chosen as analytes of interest. The performance of sensors has been validated in the lab and field tests, proving the capability of the sensors to be used for personal exposure monitoring.Dissertation/Thesis
Doctoral Dissertation Chemistry 2019
34
Ponder, Jennifer B. "Colorimetric sensor array : do I see what you smell? /." 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3242962.
Full textAbstract:
Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 2006.Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6368. Adviser: Kenneth S. Suslick. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.
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"A Portable Colorimetric Sensing Platform for the Evaluation of Carbon Dioxide in Breath." Doctoral diss., 2017. http://hdl.handle.net/2286/R.I.44315.
Full textAbstract:
abstract: This work describes the development of a device for measuring CO2 in breath, which has applications in monitoring a variety of health issues, such as Chronic Obstructive Pulmonary Disease (COPD), asthma, and cardiovascular disease. The device takes advantage of colorimetric sensing technology in order to maintain a low cost and high user-friendliness. The sensor consists of a pH dye, reactive element, and base coated on a highly porous Teflon membrane. The transmittance of the sensor is measured in the device via a simple LED/photodiode system, along with the flow rate, ambient relative humidity, and barometric pressure. The flow is measured by a newly developed flow meter described in this work, the Confined Pitot Tube (CPT) flow meter, which provides a high accuracy with reduced flow-resistance with a standard differential pressure transducer. I demonstrate in this work that the system has a high sensitivity, high specificity, fast time-response, high reproducibility, and good stability. The sensor has a simple calibration method which requires no action by the user, and utilizes a sophisticated, yet lightweight, model in order to predict temperature changes on the sensor during breathing and track changes in water content. It is shown to be effective for measuring CO2 waveform parameters on a breath-by-breath basis, such as End-Tidal CO2, Alveolar Plateau Slope, and Beginning Exhalation Slope.Dissertation/Thesis
Doctoral Dissertation Chemical Engineering 2017
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Cosby, Daniel. "Adulterants and interpretive challenges in forensic science: effects on colorimetric spot tests for presumptive drug identification and adverse side effects in the body." Thesis, 2014. https://hdl.handle.net/2144/14385.
Full textAbstract:
A common practice amongst street drug manufacturers and dealers is to combine the illicit drug of abuse they intend to distribute with additional substances. Substances added in an attempt to mimic or enhance the desired effect of the drug of abuse are known as adulterants as opposed to diluents, which are added simply to increase the weight of the product. By definition, an adulterant has a physiological effect on the body and as physiologically active compounds these adulterants may have side effects apart from the drug it is added to. They can be minimal, treatable, or otherwise manageable while others can be worse than those incurred from the drug of abuse itself.
Due to varying trends in street drug purity, an effort must be made to understand the effects adulterants and diluents, as well as mixtures thereof, may have on forensic drug analysis. Colorimetric spot test analysis is typically performed using a representative sample of the raw, suspected drug material. These tests are often employed in the lab prior to any attempt to isolate a specific compound or at the scene before an arrest is made. This being the case, the reagents will be exposed to and have the potential to react with anything present in the sample with the drug of abuse. While much work has been done regarding the specificity and cross reactivity of colorimetric spot tests, limited information is available about how mixtures of adulterants may affect the results.
This research consists of two parts which approach the common theme of adulterants differently. The first part is a literature based investigation into the pathological side effects of several common drug adulterants. The specific compounds discussed are: levamisole, phenacetin, atropine, and several topical anesthetics (benzocaine, lidocaine, prilocaine, and procaine). A review of articles from the scientific literature was conducted in order to convey what is known in the medical field regarding the effects these compounds can have on the body. The second part of this research was a laboratory based investigation which analyzed the effects of twenty-three common adulterants on two colorimetric spot tests: the Marquis reagent for the presumptive identification of heroin, morphine, amphetamine, methamphetamine, and 3,4-methylenedioxy-N-methamphetamine (MDMA) and the modified Scott test for the presumptive identification of cocaine. This was performed in order to observe the reactivity of these compounds so that a better understanding of the effect their presence can have on the analysis of seized drug samples using these tests could be obtained.
The literature review portion of this research revealed that the adulterants levamisole, atropine, phenacetin, and the topical anesthetic adulterants lidocaine, prilocaine, benzocaine, and procaine, can be toxic and have severe, deleterious effects on the body in both chronic and acute exposures. Levamisole stimulates the immune system resulting in the production of self-reactive antibodies that attack neutrophils. This causes an autoimmune disorder that weakens the immune system and causes leukocyte agglutination leading to necrotizing vasculitis. Atropine functions to decrease the parasympathetic tone and increase the sympathetic tone in the body. An overdose can cause anticholinergic toxicity, a syndrome very similar to sympathomimetic toxidrome caused by cocaine overdose. Both are characterized by hypertension, hyperthermia, tachycardia, ataxia, disorientation, and mydriasis. However, they can be distinguished as anticholinergic toxicity causes dry and flush skin and mydriasis which is unreactive to light while sympathomimetic toxidrome causes profuse sweating and mydriasis which is reactive to light. Phenacetin is metabolized to O-ethyl-N-acetyl-p-benzoquinone imine (O-Et-NAPQI), a highly reactive and unstable electrophile. It is capable of covalently binding with proteins and other cellular components, including deoxyribonucleic acid (DNA). This leads to mutagenesis and subsequent tumor generation as well as apoptosis and necrosis of various tissues in the bladder and kidneys. The topical anesthetics have each been associated with the development of methemoglobinemia. This is a condition caused by an increase in the concentration of methemoglobin in the blood. Methemoglobin binds more strongly to oxygen so that it cannot be released to the tissues resulting in oxygen starvation. This was found to be caused by the metabolism of prilocaine and lidocaine to the oxidative compounds O-toluidine and 2,6-xylidine respectively. The cause has not been previously reported for benzocaine or procaine.
The laboratory portion of this research revealed the impact several adulterants and their mixtures can have on colorimetric spot tests. Testing with approximately 1 mg of sample material revealed that eight out of the twenty-three adulterants reacted with the Marquis reagent to cause a color change within 15 minutes. Of the ten 3-component mixtures tested, eight resulted in a color change. Of the six five-component mixtures, four resulted in a color change; of the six eight-component mixtures, three resulted in a color change; and of the six ten-component mixtures, five resulted in a color change. Of the color changes observed, none were consistent with the "expected" color change for a presumptively positive result of the Marquis test.
Testing with the adulterant diphenhydramine revealed that this compound had a unique and intense reaction with the Marquis reagent. This compound initially reacted by turning the liquid a vibrant yellow-green upon contact with the sample. Prior to 2 minutes, solid red-brown aggregates formed in the liquid and proceeded to increase in size while the reagent solution darkened to a red-black color over the 15 minutes of observation. Mixtures containing diphenhydramine each reacted differently. Solid material did not form in the mixture tests and the color changes observed ranged from light orange to a dark red-orange. In addition, one 3-component mixture containing adulterants which did not cause a color change when tested individually (diltiazem, acetaminophen, and quinine) was observed to cause a light brown color to develop, which darkened over the 15 minutes of observation.
The results for the modified Scott test showed that the complexity of this test has made it highly specific for cocaine. None of the individual components or mixtures tested reacted in a manner consistent with a presumptively positive identification for cocaine hydrochloride (HCl) or cocaine base for all three steps. Of the twenty-three adulterants tested, eight of the twenty-three gave a similar result to cocaine base in step 1, however, of these eight, only one (quinine) gave a similar result to cocaine base in step 2, and this adulterant did not react consistently to cocaine base in step 3. The research using the adulterant mixtures revealed that the compounds present in these samples tended to react individually with the modified Scott test reagents. In other words, the results for each mixture appeared as a combination of the individual results for each component.
While the results observed for the adulterants and mixtures tested were not consistent with the expected presumptively positive results for the drugs these tests are used to detect, it was concluded that the presence of adulterants in a sample has the potential to affect the results of a colorimetric spot test in a variety of ways. Given that these tests are typically employed on samples of raw suspected drug material, it is important that analysts understand the impact adulterants can have on the interpretation of presumptive drug tests.
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Kaur, Daljit. "Development of a cheap and rapid method to determine calcium in milk fractions in an industrial environment." 2007. http://hdl.handle.net/10292/742.
Full textAbstract:
Milk contains high concentrations of calcium. It occurs in two forms, a free ionic form, and calcium associated with milk proteins (caseins). The latter association is called colloidal calcium phosphate. New Zealand Dairy Foods of Takanini is marketing a range of commercial milks in supermarkets. The company uses ultra filtration to concentrate milk proteins and calcium in different milk products. During ultra filtration, the fraction that is retained by the membrane is rich in calcium bound to proteins and the portion that passes through the membrane is richer in the free ionic form. The company wanted to develop a quick and an economical method that can be applied in industrial settings to determine calcium in both these fractions and in other milk products. This research aimed to develop a quick, wet chemistry method to measure calcium in milk fractions and to trial it in an industrial environment. Two methods, the so-called EDTA method and the atomic absorption spectrophotometric method (AA) were trialled as potential reference methods against which to compare results obtained by the method to be developed. The AA method was chosen due to its ease, accuracy and precision. (This could not be selected as the industrial method for a number of reasons.) A colorimetric method was favoured over other contenders. Two colorimetric dyes, Arsenazo I and o-cresolphthalein-complexone (CPC) were chosen to work with. Arsenazo I forms a purple complex with calcium in a suitable buffer at a range of pHs. o-Cresolphthalein-complexone also forms purple-coloured complexes at alkaline pHs. During method development with Arsenazo I, different buffers were trialled and a NaOH/ KCl buffer was selected for further development at pH 12. The method worked well during the development phase but with some inconsistent results at times. o-Cresolphthalein-complexone formed clear purple complexes with Clark and Lubs and 2-amino-2-methylpropanol (AMP) buffers. The key advantage of the CPC dye with AMP buffer was that when 8-hydroxyquinoline was included in the reaction mixture, it successfully masked coloured complex formation due to CPC with magnesium, which is present in milk at about 1/3 the calcium concentration. This effect did not work with Arsenazo I. However, the results obtained with the CPC method were lower than claimed values of most milks trialled during development. Both methods were compared for their precision and it was found that CPC method has better precision and was chosen for further development. To improve the accuracy and precision, various denaturing reagents were used to (hypothetically) release calcium from the caseins. Trichloroacetic acid at 25 % was more effective than the several other denaturing treatments tested. The finalised CPC method, using trichloroacetic acid, AMP and 8-hydroxyquinoline, was then used to monitor calcium concentration over four months in three milk products, skim, Xtra (retentate) and permeate. For all milks, the CPC values were lower than the AA reference values, and the values reported by a commercial analytical laboratory. The reasons for this are discussed, as are other changes in calcium concentration in the three milks throughout the trial. The correlation between the CPC and AA values was poor for Xtra, better for skim, and best for permeate. A chemical model to explain this is discussed. The method developed is cheap and quick, and sample and reagent preparation is simple. The method could be applied in an industrial environment, but a proportionality factor would have to be applied to account for the difference in mean values between the CPC and AA methods.
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"Portable Sensors for Breath Analysis." Doctoral diss., 2013. http://hdl.handle.net/2286/R.I.18813.
Full textAbstract:
abstract: Human breath is a concoction of thousands of compounds having in it a breath-print of physiological processes in the body. Though breath provides a non-invasive and easy to handle biological fluid, its analysis for clinical diagnosis is not very common. Partly the reason for this absence is unavailability of cost effective and convenient tools for such analysis. Scientific literature is full of novel sensor ideas but it is challenging to develop a working device, which are few. These challenges include trace level detection, presence of hundreds of interfering compounds, excessive humidity, different sampling regulations and personal variability. To meet these challenges as well as deliver a low cost solution, optical sensors based on specific colorimetric chemical reactions on mesoporous membranes have been developed. Sensor hardware utilizing cost effective and ubiquitously available light source (LED) and detector (webcam/photo diodes) has been developed and optimized for sensitive detection. Sample conditioning mouthpiece suitable for portable sensors is developed and integrated. The sensors are capable of communication with mobile phones realizing the idea of m-health for easy personal health monitoring in free living conditions. Nitric oxide and Acetone are chosen as analytes of interest. Nitric oxide levels in the breath correlate with lung inflammation which makes it useful for asthma management. Acetone levels increase during ketosis resulting from fat metabolism in the body. Monitoring breath acetone thus provides useful information to people with type1 diabetes, epileptic children on ketogenic diets and people following fitness plans for weight loss.Dissertation/Thesis
Ph.D. Chemistry 2013
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Zhang, Yufen. "Development of an enzyme immobilization platform based on microencapsulation for paper-based biosensors." Thèse, 2011. http://hdl.handle.net/1866/9883.
Full textAbstract:
Un papier bioactif est obtenu par la modification d’un papier en y immobilisant une ou plusieurs biomolécules. La recherche et le développement de papiers bioactifs est en plein essor car le papier est un substrat peu dispendieux qui est déjà d’usage très répandu à travers le monde. Bien que les papiers bioactifs n’aient pas connus de succès commercial depuis la mise en marche de bandelettes mesurant le taux de glucose dans les années cinquante, de nombreux groupes de recherche travaillent à immobiliser des biomolécules sur le papier pour obtenir un papier bioactif qui est abordable et possède une bonne durée de vie. Contrairement à la glucose oxidase, l’enzyme utilisée sur ces bandelettes, la majorité des biomolécules sont très fragiles et perdent leur activité très rapidement lorsqu’immobilisées sur des papiers. Le développement de nouveaux papiers bioactifs pouvant détecter des substances d’intérêt ou même désactiver des pathogènes dépend donc de découverte de nouvelles techniques d’immobilisation des biomolécules permettant de maintenir leur activité tout en étant applicable dans la chaîne de production actuelle des papiers fins.
Le but de cette thèse est de développer une technique d’immobilisation efficace et versatile, permettant de protéger l’activité de biomolécules incorporées sur des papiers. La microencapsulation a été choisie comme technique d’immobilisation car elle permet d’enfermer de grandes quantités de biomolécules à l’intérieur d’une sphère poreuse permettant leur protection. Pour cette étude, le polymère poly(éthylènediimine) a été choisi afin de générer la paroi des microcapsules. Les enzymes laccase et glucose oxidase, dont les propriétés sont bien établies, seront utilisées comme biomolécules test. Dans un premier temps, deux procédures d’encapsulation ont été développées puis étudiées. La méthode par émulsion produit des microcapsules de plus petits diamètres que la méthode par encapsulation utilisant un encapsulateur, bien que cette dernière offre une meilleure efficacité d’encapsulation. Par la suite, l’effet de la procédure d’encapsulation sur l’activité enzymatique et la stabilité thermique des enzymes a été étudié à cause de l’importance du maintien de l’activité sur le développement d’une plateforme d’immobilisation. L’effet de la nature du polymère utilisé pour la fabrication des capsules sur la conformation de l’enzyme a été étudié pour la première fois.
Finalement, l’applicabilité des microcapsules de poly(éthylèneimine) dans la confection de papiers bioactifs a été démontré par le biais de trois prototypes. Un papier réagissant au glucose a été obtenu en immobilisant des microcapsules contenant l’enzyme glucose oxidase. Un papier sensible à l’enzyme neuraminidase pour la détection de la vaginose bactérienne avec une plus grande stabilité durant l’entreposage a été fait en encapsulant les réactifs colorimétriques dans des capsules de poly(éthylèneimine). L’utilisation de microcapsules pour l’immobilisation d’anticorps a également été étudiée.
Les avancées au niveau de la plateforme d’immobilisation de biomolécules par microencapsulation qui ont été réalisées lors de cette thèse permettront de mieux comprendre l’effet des réactifs impliqués dans la procédure de microencapsulation sur la stabilité, l’activité et la conformation des biomolécules. Les résultats obtenus démontrent que la plateforme d’immobilisation développée peut être appliquée pour la confection de nouveaux papiers bioactifs.Biosensing paper attracts increasing attention due to its benefits of being simple, visible, portable and useful for detecting various contaminants, pathogens and toxins. While there has been no bioactive paper commercialized since glucose paper strips developed in the fifties, many research groups are working to immobilize biomolecules on paper to achieve a bioactive paper that is affordable and has good shelf life. The goal of this research is to develop some highly useful bioactive paper that could, for example, measure blood glucose, or immediately detect and simultaneously deactivate pathogens such as neuraminidase and E.coli. Previously, bioactive paper was produced either through physically absorbing biorecognition elements or printing bio-ink onto paper substrate. Our methodology for fabrication of bioactive paper strips is compatible with existing paper making process and includes three procedures: the fabrication of microcapsules, enzyme or antibody microencapsulation, immobilization of enzymes or antibody-entrapped microcapsules into paper pulp. The first step, in fabricating of bioactive paper strips is to produce biocompatible and inexpensive microcapsules with suitable parameters. To do so, two types of microencapsulation methods were compared; the emulsion method and the vibration nozzle method accomplished with an encapsulator. The parameters for producing optimal microcapsules with both methods were studied. Factors that affect their diameter, wall thickness, shell pore size, encapsulation efficiency and membrane compositions were also discussed. By comparison, microcapsules prepared with poly(ethyleneimine) (PEI) by the emulsion method exhibit properties that were more suitable for enzyme encapsulation and paper making process, whereas the microcapsules prepared by the vibration nozzle method were too big to be immobilized within paper pulp, and had lower encapsulation efficiency, enzymatic activity and productivity. Thus the emulsion method was chosen for subsequent experiments such as enzyme and antibody microencapsulation and bacterial vaginosis (BV) paper preparation. Microcapsules made by the emulsion method were semi-permeable in that the diffusion of substrate and product molecules were allowed freely across the membranes but the encapsulated enzymes would be retained inside. Glucose oxidase from Aspergillus niger (GOx) and laccase from Trametes versicolor (TvL) microcapsules showed high encapsulation efficiency, but the encapsulation process caused a severe decrease in the specific activities of both enzymes. Results from circular dichroism (CD) studies, fluorescence properties, enzymatic activities of free enzymes and Michaelis-Menten behavior demonstrated that the Vmax decrease for GOx was due to the restriction of diffusion across microcapsule membranes with pore size less than 5 nm. The microencapsulation process improved the thermal stability of GOx but decreased that of laccase. Bioactive papers were fabricated either by incorporating microcapsules containing different enzymes or empty microcapsules soaked in substrate and enhancer solution into the paper pulp during the sheet making process. Both the GOx and the BV paper strips underwent a color change in the presence of glucose and potassium iodide, and sialidase from Clostridium perfringens respectively. Some preliminary studies on antibody sensitized microcapsules, in which antibody was either encapsulated within the PEI microcapsules or conjugated to its membranes, were also performed. Our objective was to establish an enzyme immobilization platform based on microencapsulation techniques for paper based biosensors. Even though our current studies only focused on the microencapsulation of two enzymes, TvL and GOx, as well as the bioactive paper preparation, a similar approach can be applied to other enzymes. We believe that this immobilization method can potentially be employed for bioactive paper preparation on an industrial scale.
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"Novel Gas Sensor Solutions for Air Quality Monitoring." Doctoral diss., 2020. http://hdl.handle.net/2286/R.I.62951.
Full textAbstract:
abstract: Global industrialization and urbanization have led to increased levels of air pollution. The costs to society have come in the form of environmental damage, healthcare expenses, lost productivity, and premature mortality. Measuring pollutants is an important task for identifying its sources, warning individuals about dangerous exposure levels, and providing epidemiologists with data to link pollutants with diseases. Current methods for monitoring air pollution are inadequate though. They rely on expensive, complex instrumentation at limited fixed monitoring sites that do not capture the true spatial and temporal variation. Furthermore, the fixed outdoor monitoring sites cannot warn individuals about indoor air quality or exposure to chemicals at worksites. Recent advances in manufacturing and computing technology have allowed new classes of low-cost miniature gas sensor to emerge as possible alternatives. For these to be successful however, there must be innovations in the sensors themselves that improve reliability, operation, and their stability and selectivity in real environments. Three novel gas sensor solutions are presented. The first is the development of a wearable personal exposure monitor using all commercially available components, including two metal oxide semiconductor gas sensors. The device monitors known asthma triggers: ozone, total volatile organic compounds, temperature, humidity, and activity level. Primary focus is placed on the ozone sensor, which requires special circuits, heating algorithm, and calibration to remove temperature and humidity interferences. Eight devices are tested in multiple field tests. The second is the creation of a new compact optoelectronic gas sensing platform using colorimetric microdroplets printed on the surface of a complementary-metal-oxide-semiconductor (CMOS) imager. The nonvolatile liquid microdroplets provide a homogeneous, uniform environment that is ideal for colorimetric reactions and lensless optical measurements. To demonstrate one type of possible indicating system gaseous ammonia is detected by complexation with Cu(II). The third project continues work on the CMOS imager optoelectronic platform and develops a more robust sensing system utilizing hydrophobic aerogel particles. Ammonia is detected colorimetrically by its reaction with a molecular dye, with additives and surface treatments enhancing uniformity of the printed films. Future work presented at the end describes a new biological particle sensing system using the CMOS imager.Dissertation/Thesis
Doctoral Dissertation Materials Science and Engineering 2020