A series of fluorescent probes based on different signal transduction mechanisms for the detection of Fe3+, Zn2+, histidine and pH was designed and synthesized. Their photophysical properties, binding abilities and the further application in cell imaging were fully evaluated. Building on the groundwork of our previous study, molecular scaffold 19 has been appended to spirobenzopyran fluorophore to furnish a highly selective and sensitive Zn2+ sensor. To broaden the application scope of this trifunctional receptive molecule, 19 was incorporated onto rhodamine, antipyrine and coumarin moieties to give 20, 21 and 23, respectively. Probe 20 operative on a chelation-enhanced fluorescence mechanism exhibited highly selective response to Fe3+ with 2:1 stoichiometry of 20-Fe3+ complex. However, a possible tendency of probe 20 to hydrolyze induced by Fe3+ and the unsuccessful attempt of cell imaging would limit its application scope. Probe 21 with O-N-N-N-N-ligand showed a highly selective and sensitive detection of Zn2+. The probe displayed suppressed response to Cd2+ which is the most common interference ion in zinc metal detection. The binding of Zn2+ to probe 21 inhibited the photoinduced electron transfer process originating from the lone pair of the nitrogen atom in the antipyrine moiety to quinoline fluorophore. Therefore, a turn-on fluorescent probe was developed. A moderate binding constant with 1:1 stoichiometry of 21-Zn2+ complex was established by fluorescence titration. The binding mechanism was fully explained by 1H NMR titration. To our delight, probe 21 was successfully applied for recognizing Zn2+ in living cells. The preparation of probe 23 was achieved by appendage of 19 to coumarin derived fluorophore and the probe exhibited a good selectivity and fluorescent turn-off property to Cu2+. The 1:1 stoichiometry of 23-Cu2+ ensemble can serve as an efficient probe for the detection of histidine and biothiols. In the presence of NEM, the influence of biothiols could be eliminated. Furthermore, this sensing ensemble was also used in the detection of histidine in hard-to-transfect U87MG cells with very low cytotoxicity. Based on our group’s previous work on the spiropyran platform, a novel ratiometric near-infrared pH probe 27 operating on an excited-state intramolecular electron transfer mechanism was developed. The pKa was calculated to be 5.9 and the ring-opening/ring-closing mechanism triggered by protons was reasonably explained by 1H NMR titration. However, this spiropyran-based probe was found to be unsuitable for cell imaging. To continue the innovation of pH sensing and extend its application in bioimaging, a series of ratiometric pH probes 32 and 38 characterized by their high quantum yield working in the NIR range was developed. The appendage of N,O-disubstituted hemiaminal ether moiety onto coumarin fluorophore with C=C double bond conferred the sensory material with the ability to display a pH-dependent ratiometric output operating on the ring-opening/ring-closing mechanism. The pKa of 32 and 38 were 6.9 and 5.8 – 6.0, respectively, which rendered them suitable for pH measurement in near-neutral and acidic media. A preliminary work of intracellular pH measurement was also conducted and promising results were obtained

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The use of a microchannel plate as an optical encoding device has many advantages. These include large surface area and large-scale signal averaging. This instrument was designed to obtain and interpret the information generated by the optical transform of a microchannel plate. It will be shown that a large amount of information about solution interactions and properties can be obtained from such an instrument. / Master of Science

This investigation was concerned with the development of a fiber optic evanescent sensor. Such a sensor is based upon the lateral regions of the waveguide and their interaction with a chemical environment. The basic principles and concepts involved in the construction of a fiber optic spectroscopic evanescent field sensor are developed. From this fundamental knowledge a series of sensors were constructed to characterize their responses. First, the response to simple refractive index changes and angle launch conditions were explored. This demonstrated the light interaction with the measurement environment. What followed was the use of these sensors to make spectrochemical absorption measurements suitable for a calibration curve of 1.25 x 10⁻² to 1.22 x 10⁻⁹ M concentrations for various dye systems. As a consequence of the spectrochemical studies the unique interaction between the chemical environment and the silica surface was observed. This response is based upon the chemical reactivity of the silica surface and the chemical environment. This prompted the investigation of the ion exchange characteristics of the silica waveguide surface and the chemical environment. In this investigation the exchange selectivities of the alkali, alkali earth and lanthanide metals were determined. Finally, a series of innovative fiber optic sensors base upon interferometric and refractometric measurements were investigated. These designs were based upon the fabrication characteristics of glass and plastic fiber optic waveguides. / Ph. D.

A Thesis submitted for the faculty of Science at the University of Witwatersrand Johannesburg, in the fulfilment for the degree of Doctor of Philosophy in Chemistry. Johannesburg, November 2016. / The synthesis of carbon spheres (solid and hollow) for application in organic photovoltaics and chemical sensors is a means of using inexpensive and readily processable carbons to eliminate global warming and to monitor harmful gases. The synthesis conditions used to make solid carbon spheres can also be used to tailor their structural, paramagnetic and thermal properties. More so, the ability to tailor the morphology, surface, structural and electronic properties of the hollow carbon spheres by a templating method is an added advantage to their applicability in electronic devices. Solid carbon spheres were synthesized by a vertically oriented chemical vapor deposition (CVD) reactor using acetylene as a carbon source and argon or hydrogen as the carrier gas. The flow rates of the acetylene or carrier gases determined the particle sizes of the carbon spheres. Annealing of carbon spheres in hydrogen resulted in an increase in thermal stability, fewer defects and narrower paramagnetic signals relative to the carbon spheres annealed in argon gas. In contrast, carbon spheres annealed in argon exhibited an increase in the number of defects, a decrease in thermal stability and broader paramagnetic signals. Doped carbon spheres portrayed an increase in ID/IG ratios, a decrease in thermal stability and stronger paramagnetic signals due to the presence of defects induced by nitrogen. The N doped carbon spheres synthesized in H2 comprised of 48% pyridinic-N, 22% pyrrolic-N and 24% quaternary -N while the N doped spheres obtained in the presence of Ar had 17% pyridinic- N, 20% pyrrolic-N and 49% quaternary-N. The presence of a higher percentage of pyridinic- N confirms the presence of more edge defects in carbon spheres synthesized under H2 gas corroborating with the stronger paramagnetic signal observed from the ESR spectra. Consequently, a higher N/C ratio was exhibited in the N doped CSs obtained in the presence of H2 (4.96) than in the presence of Ar (3.68). This could be attributed to the presence of edge defects in carbon spheres synthesized in the presence of H2 gas. The induction of edge defects in carbon spheres in the presence of H2 gas without the aid of a metal catalyst opens a platform for regulating surface and catalytic reactions using H2 gas. Pristine and mesoporous SiO2 spheres were synthesized using a modified Stober method. Carbonization of the pristine SiO2, pristine SiO2@PVP, mesoporous SiO2 and mesoporous SiO2@PVP spheres was carried out using a bubbling method with toluene as the carbon source and argon as the carrier gas in a CVD reactor for 1 h. Upon SiO2 removal, hollow carbon nanostructures of varying morphologies were obtained. The polyvinylpyrrolidone (PVP) adsorption time, PVP concentration, SiO2 mesoporosity, SiO2 particle size dispersion, and carbonization time played a role in the formation of unique hollow carbon nanostructures; complete HCSs, broken HCSs, deformed HCSs, edge connected, open ended, wormlike and bubble-like HCSs. The mesoporous broken HCSs and open ended HCSs portrayed a hierarchical structure with a bimodal pore size distribution. The surface area properties of these materials and the ease of control of the carbon morphology gives an insight into the application of these materials as dye adsorbents. The effect of the size dispersion of Au@SiO2 sphere templates for the synthesis of hollow carbon structures was evaluated using a CVD nanocasting method. The diameter of the template, the presence of the gold nanoparticles and the amount of PVP determined the size, thickness and shape of the synthesized carbon nanostructures. Carbonization (and SiO2 removal) of Au@polydispersed silica spheres for 1 h gave a graphene-like HCS layer while longer times (2-4 h) gave nanotube like (or worm like) HCSs. These results highlight the potential use of Au@carbon core shell structures for the generation of few layered graphene-like unusual nanostructures. As a proof of concept, the wormlike carbon structures were incorporated in organic solar cells and found to give a measurable photovoltaic response. The incorporation of Au nanospheres and nanorods in a hole transport layer (PEDOT:PSS) of a solar cell device increased the current density and the photo-conversion efficiency of the device due to the local surface plasmon resonance and enhanced light scattering effects of gold. However, high series resistance and leakage currents were obtained due to barrier centres created by uneven dispersion of Au nanaorods within the polymer matrix. The performance of bulk heterojunction organic photovoltaic cells based on poly(3-hexylthiophene- 2,5-diyl) (P3HT) and 6,6-phenyl-C61-butyric acid methyl ester (PCBM) processed from chlorobenzene solution can be enhanced by solution heat treatment of the blend. The morphology of films spin coated from the heat treated blend solution reveals a more favourable diffusion of PCBM into the P3HT matrix than heating of the individual solutions separately. The films obtained from heat treated P3HT and PCBM solutions had a more homogeneous dispersion and enhanced light absorption than those obtained from solutions heat treated separately. There was a significant improvement in the performance for devices made from a solution heat treated blends relative to the non-treated blend; a maximum power conversion efficiency of 3.5% and a fill factor up to 43% was achieved under Air Mass 1.5 at 100 mW/cm2 illumination. This study also reports on the sensing characteristics of ammonia in humid environment by hollow carbon spheres, hollow carbon spheres-polyvinylpyrrolidone composite and annealed hollow carbon spheres, at 20°C and 40°C. For device fabrication, a surfactant assisted method was used to homogeneously disperse the hollow carbon spheres, allowing their deposition onto an interdigitated electrode by casting. An enhanced response and recovery time of the devices was observed at the higher working temperature. Annealing of the hollow carbon spheres resulted in a tremendous decrease in the humidity dependent ammonia sensing due to a decrease in the number of the oxygenated groups and defects in their structure. The presence of hydroxyl groups on the pristine hollow carbon sphere surface resulted in an enhanced proton conductivity. However, the ammonia sensitivity at high relative humidity in the pristine hollow carbon spheres is negligible due to the inhibition of ammonia adsorption sites by the high concentration of water molecules. The sensor response was investigated by varying both ammonia concentration and relative humidity, determining the topology of the response as a function of these two variables, and applying a tristimulus analysis in an attempt to determine the ammonia concentration independently of the relative humidity. This study demonstrates the critical role played by humidity and surface chemistry in the ammonia sensing properties of hollow carbon spheres. The studies reveal the day to day application of ammonia sensors, with temperature and humidity playing a critical role in the carbon based sensor response and recovery of the materials. These carbon based sensors that simultaneously measure ammonia and relative humidity could be applied in agricultural industries to monitor ammonia concentration in soils, fishponds and in food industries to monitor meat spoilage. / LG2017

Image segmentation is the process by which an image is divided into number of regions. The regions are to be homogeneous with respect to some property. Definition of homogeneity depends mainly on the expected patterns of the objects of interest. The algorithms designed to perform these tasks can be divided into two main families: Splitting Algorithms and Merging Algorithms. The latter comprises seeded region growing algorithms which provide the basis for our work. Seeded region growing methods such as Marker initiated Watershed segmentation depend principally on the quality and relevance of the initial seeds. In situations where the image contains a variety of aggregated objects of different shapes, finding reliable initial seeds can be a very complex task. This thesis describes a versatile approach for finding initial seeds on images featuring objects distinguishable by their structural and intensity profiles. This approach involves the use of hierarchical trees containing various information on the objects in the image. These trees can be searched for specific pattern to generate the initial seeds required to perform a reliable region growing process. Segmentation results are shown in this thesis. The above image segmentation scheme has been applied to detect isolated living cells in a sequence of frames and monitor their behavior through the time. The tissues utilized for these studies are isolated from the scales of Betta Splendens fish family. Since the isolated cells or chromatophores are sensitive to various kinds of toxic agents, a creation of cell-based toxin detector was suggested. Such sensor operation depends on an efficient segmentation of cell images and extraction of pertinent visual features. Our ultimate objective is to model and classify the observed cell behavior in order to detect and recognize biological or chemical agents affecting the cells. Some possible modelling and classification approaches are presented in this thesis. / Graduation date: 2003

Thesis (Ph.D)--Civil and Environmental Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Aral, Mustafa; Committee Member: Guan, Jiabao; Committee Member: Jang, Wonyong; Committee Member: Kim, Seong-Hee; Committee Member: Uzer, Turgay. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Over the past two decades, the field of molecular sensing has developed into a mature offshoot of molecular recognition, and sensing protocols based on optical signal modulations have enjoyed particularly great success. Such sensing methods are the focus of this dissertation, in which efforts toward the integration of dendrimers and reactands into separate, optically-based sensing platforms are described. To this end, Chapter 1 provides a brief introduction to molecular sensing and its supramolecular underpinnings. The remainder of Chapter 1 is dedicated to dendrimers and their application to molecular recognition and sensing. A discussion of the physicochemical properties of dendrimers is also included to lend perspective on the structure, size, and shape of these macromolecules. The role of dyes and indicators in the elucidation of dendritic structure and function is given special consideration. Finally, selected reports of dendrimers in molecular recognition and optical sensing are summarized. Chapter 2 details original research directed toward the incorporation of dendrimers into molecular sensing ensembles. This use of dendrimers in molecular recognition and sensing is distinguished from those examples described in Chapter 1 by its modular nature. This modularity is achieved through the use of a non-covalent sensing motif based on indicator displacement. The identification and optimization of the appropriate components for use in such dendrimer-based sensing ensembles represents a contribution of the research described herein. An evaluation of indicator dyes for their incorporation into an enantioselective indicator displacement assay (eIDA) for common organic molecules is the subject of the research discussed in Chapter 3. The selected indicator dyes were assessed for use in a novel eIDA that relies on covalent bond formation for the enantioselective signaling of monofunctional organic analytes. A survey of colorimetric methods for the identification and discrimination of amines is included because these compounds served as an initial target in the proposed assay. Optical enantiosensing strategies are also reviewed in light of their relevance to the present work. / text