A Coulostatic Impulse Generator (CIG) is an electronic device that transfers electrical charge to and from a pair of electrodes inserted in plant tissue. Six discrete charge transfers can be implemented in any desired sequence. The major purpose of the CIG is to determine the electrochemical constituents of the plant apoplast electrolyte. The objective of this thesis is threefold: (1) to design, construct and test the supervisory circuitry of the CIG, (2) to design, construct and test the interface between the NEC portable computer and the CIG, (3) to generate utility software to control each circuit board in the system. To handle the extreme difference in the timing of the charge transfer (microseconds) and the subsequent plant response a three step timing sequence is employed which permits an independent range of sample times and sample numbers. Data acquired is first stored in RAM in the computer within the CIG and then transferred to the external computer. (Abstract shortened with permission of author.)

Les travaux de cette thèse portent sur l'élaboration de capteurs électrochimiques pour la détection de micropolluants mis sous surveillance par la Directive Cadre sur l'Eau (DCE/200/60/CE) tels que Ni(II) et Pb(II). Actuellement, le contrôle des eaux est effectué par prélèvements cependant les méthodes d'analyses sont longues et coûteuses et les seuils de concentration très faibles imposés par la loi, nécessitent d’avoir recourt à d’autres types d’équipements, tels que les capteurs électrochimiques. L'amélioration indispensable de leur sensibilité et de leur sélectivité peut être atteinte par le choix du matériau d'électrode et de sa fonctionnalisation de surface. Ces capteurs ont pour objectif, à terme, d’analyser la qualité des eaux sur site en continu ou semi-continu. Dans le cas de l'étude de la sélectivité, les sels de diazonium ont été choisis pour le greffage des fonctions benzamides oximes, complexantes du Ni(II). Cette molécule n'ayant jamais été étudiée électro-chimiquement, son domaine d'électro-activité et les mécanismes d'oxydation ont été étudiés. Les électrodes greffées ont permis la détection électrochimique et montrent une sélectivité pour le Ni(II), en présence d'interférents comme Pb(II) et Cu(II). Cette étude a prouvé que les amines aromatiques et aliphatiques peuvent être greffées par oxydation en milieux aqueux. Les électrodes ainsi fonctionnalisées ont montré que la mobilité des fonctions complexantes, via la structure et la longueur du squelette carboné, influence la limite de détection des capteurs, les chaînes aliphatiques complexant particulièrement bien les cations métalliques. Enfin, l’influence de différentes formes allotropiques du carbone, utilisées en tant que phases actives d’électrodes sérigraphiées, a été étudié. Des électrodes composées de différentes formes allotropiques de carbones ont été fonctionnalisées par des sels de diazonium et utilisées pour la détection du Pb(II). Les résultats montrent que certains matériaux carbonés, comme les nanotubes de carbone, améliorent les propriétés électro-catalytiques des capteurs. / This work is focused on the elaboration of electrochemical sensors for Ni(II) and Pb(II) micropollutants detection, targeted by the Water Framework Directive (WFD 2000/60/CE). Currently, water supervision is carried out by sampling and analytical equipments, however these methods are too long and too expensive, the very low concentration limits imposed by laws, needed to be reached using other kind of equipments such as electrochemical sensors. The sensitivity and selectivity of these sensors can be improved by the choice of the electrode materials and their surface functionalization. The aim of these sensors is to make possible the water quality analysis on site, continuously or semi-continuously. The selectivity was reached by grafting diazonium salts composed of benzamide oxime functions, complexing Ni(II). The electro-activity area and the oxidation mechanisms of this molecule were investigated. It is to be underlined that the electrochemical behavior of this molecule has never been studied in the litterature. The grafted electrodes were used for the electrochemical detection, and they turned out to be selective for Ni(II) detection in the presence of both Pb(II) and Cu(II). To improve the sensitivity of these sensors, the mobility of the complexing function is important. This study shows the possibility to graft aliphatic and aromatic amines via oxidation reactions in aqueous media. These electrodes revealed better analytical performances for the sensors grafted by aliphatic amines through the mobility of the carbon chains complexing metallic cations. Finally, the influence of the different allotropic kind of carbons, used as screen printing electrodes, were compared. These electrodes, functionalized with diazonium salts and used for the detection of the Pb (II) showed that some carbonaceous materials such as carbon nanotubes, improve the electro-catalytic properties of the sensors.

The sensing needs for the fresh produce industry can be split into two primary stages: during maturation in the field, also referred to as Precision Farming, and during storage and transport of the produce, or Postharvest Storage. This work seeks to improve the accuracy and reliability of commercially available electrochemical and spectroscopic sensors tailored to the sensing needs of the fresh produce industry. For electrochemical sensing, this study proposes the use of an inline filter to remove polar organic compounds, which can interfere with the readings of a platinum-based electrochemical sensor. A 50% improvement in measurement accuracy was achieved when monitoring the storage headspace of a container of apples. For portable spectroscopy instruments, this study suggests improvements for the alignment of the optical bench and the spectral collect protocol. Methods to reduce the influence of environmental noise, such as variability of background light (sunlight in the field) and thermal effects on hardware performance, are presented. This study also presents the first report of the calibration transfer of spectral regressions developed with Karl Norris's Derivative Quotient Method. The motivation for this aspect of research was to develop methods to collect stable and accurate data in the field, which can be used to improve the quality of fresh produce reaching the customer and reduce premature food spoilage.

No description available.

Thesis (Ph.D.)(Chemistry)--University of Pretoria, 2004. / Title from opening screen (viewed March 18th, 2005). Includes summaries in English and Afrikaans. Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 208-222).

M.Sc. (Chemistry) / With the increase in the number of new Human Immunodeficiency Virus (HIV) infection and mortality rate worldwide partly due to diagnostic drawbacks which gives false negatives during the window period, it is imperative to find an alternative method of detection. The need for prompt, bed-side and field applicable analytical devices for biomedical purposes cannot be over emphasized in our fast paced world today. As a contribution to meeting these challenges, this dissertation reports (i) the development of novel electrochemical DNA/RNA aptamer biosensor for HIV sensing and (ii) the development of other DNA sequence specific electrochemical biosensors. These biosensors were based on composite platforms of dendrimer and gold nanoparticles...

This master’s thesis deals with the design of automated workplase for measurement with electrochemical sensors. Design and realization of a device, which communicates with computer and which can be controlled via WAN or LAN nets, are the main aims of this work. This thesis describes the process of designing, realization and optimalization of designed preparation adjustment. It also describes created software of a device, driver for service PC and programme of a web client.

In this thesis by articles, I propose and demonstrate the full design, fabrication and characterization of optical biosensors based on (Bloch) Long Range Surface Plasmon Polaritons (LRSPPs). Gold waveguides embedded in CYTOP with an etched microfluidic channel supporting LRSPPs and gold waveguides on a one-dimensional photonic crystal (1DPC) supporting Bloch LRSPPs are exploited for biosensing applications. Straight gold waveguides embedded in CYTOP supporting LRSPPs as a biosensor, are initially used to measure the kinetics constants of protein-protein interactions. The kinetics constants are extracted from binding curves using the integrated rate equation. Linear and non-linear least squares analysis are employed to obtain the kinetics constants and the results are compared. The device is also used to demonstrate enhanced assay formats (sandwich and inhibition assays) and protein concentrations as low as 10 pg/ml in solution are detected with a signal-to-noise ratio of 20 using this new optical biosensor technology. CYTOP which has a refractive index close to water is the fluoropolymer of choice in current state of the art waveguide biosensors. CYTOP has a low glass transition temperature which introduces limitations in fabrication processes. A truncated 1D photonic crystal can replace a low-index polymer cladding such as CYTOP, to support Bloch LRSPPs within the bandgap of the 1DPC over a limited ranges of wavenumber and wavelength. Motivated by quality issues with end facets, we seek to use grating couplers in a broadside coupling scheme where a laser beam emerging from an optical fiber excites Bloch LRSPPs on a Au stripe on a truncated 1D photonic crystal. Adiabatic and non-adiabatic flared stripes accommodating wide gratings size-matched to an incident Gaussian beam are designed and compared to maximise the coupling efficiency to LRSPPs. The gratings are optimized, initially, through 2D modelling using the vectorial finite element method (FEM). Different 3D grating designs were then investigated via 3D modelling using the vectorial finite difference time domain (FDTD) method. Given their compatibility with planar technologies, gratings and waveguides can be integrated into arrays of biosensors enabling multi-channel biosensing. A multi-channel platform can provide, e.g., additional measurements to improve the reliability in a disease detection problem. Thus, a novel optical biosensor based on Bloch LRSPPs on waveguide arrays integrated with electrochemical biosensors is presented. The structures were fabricated on truncated 1D photonic crystals comprised of 15 period stack of alternating layers of SiO2/Ta2O5. The optical biosensors consist of Au stripes supporting Bloch LRSPPs and integrate grating couplers as input/output means. The Au stripes also operate as a working electrode in conjunction with a neighboring Pt counter electrode to form an electrochemical sensor. The structures were fabricated using bilayer lift-off photolithography and the gratings were fabricated using overlaid e-beam lithography. The planar waveguides are integrated into arrays capable of multichannel biosensing. The wafer is covered with CYTOP as the upper cladding with etched microfluidic channels, and wafer-bonded to a borofloat silica wafer to seal the fluidic channels and enable side fluidic interfaces. The proposed device is capable in principle of simultaneous optical and electrochemical sensing and could be used to address disease detection problems using a multimodal strategy.

<p>The untethered transfer of energy and scalability of magnetic actuators enables functionality to an otherwise passive system. For example, wireless magnetic actuation can turn static 2D and 3D cell cultures into a more physiologically-relevant dynamic environment while limiting contamination. Moreover, indwelling catheters and implantable sensors are typically stationary devices that are notorious for their short lifespan when implanting into the body due to immune responses. Magnetic microactuators may be used for wireless actuation for in situ removal of biological materials accumulated on chronically implanted devices. In this dissertation, I will demonstrate examples of novel biomedical microdevices enabled by magnetic actuation for added functional benefits. First, I will describe a soft polymer magnetic actuator that can facilitate the study of a physiologically relevant cell culturing system. By cyclically stretching an extracellular matrix protein in a 3D cell culture, this system can elucidate the process by which breast cancer cells respond to a dynamic environment in the lungs. The fibrillar fibronectin suspended across the body of the magnetic actuator provides a matrix representative of early metastasis for 3D cell culture that has not yet been recapitulated in vitro until now. Our results demonstrate a clear suppressive cellular response due to cyclic stretching that has implications for a mechanical role in the dormancy and reactivation of disseminated breast cancer cells to macrometastases. As a second application, I will demonstrate the use of magnetic microactuators to remove biofouling on an implantable biosensor in order to prolong its functionality. The results of our work suggest that the motion of the actuator on the sensor surface can maintain biosensor signal integrity and prevents the downstream effects of the foreign body response. Additionally, I will present the design and proof of concept testing of a novel aspiration thrombectomy catheter meant to improve the engagement between the catheter and the blood clot being removed. Preliminary results demonstrate the added benefit of incorporating a microstructure in the inner diameter of the catheter meant to increase the retraction force aspiration catheters have when retrieving corked emboli at the catheter tip. </p> <p><br></p>