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This thesis reports the design and development of novel voltammetric pH sensors for buffered, low-buffered and unbuffered media. pH sensors in stagnant and hydrodynamic environments were designed and developed for performing measurements using square wave voltammetry. Chapter 1 introduces the motivation of this project, the current development of electrochemical sensors, and the basic theory and techniques of electrochemistry concerned within the thesis. The existing development of carbon-based electrochemical sensors and the application of screen-printing technology in sensor fabrication are highlighted. Chapter 2 introduces the screen-printing technology and the fundamental methods of numerical simulation. In addition, reagents, equipment and software packages used in the thesis are listed in this chapter. In Chapter 3, a novel design of quinone derivative-based pH probes is presented for the application in stagnant weakly buffered media (< 1mM), based on previous studies of quinone compounds in buffered media. The results from the weakly buffered system is consistent with the results in buffered systems. To further extend the application of this design in unbuffered media, a numerical model of a pH-sensitive redox particle immobilised on an electrode was developed, which predicted that the accumulation of hydrogen ions near the electrode is the possible limiting factor for the performance of this design in unbuffered media. To develop a pH-monitoring technology for unbuffered media, Chapter 4 reports on the design, fabrication and testing of different electropolymerised-phenol derivative modified electrodes, which overcome the limitation of hydrogen ions accumulation. The results revealed that 2-(methylthio)phenol graphite resin electrodes have high accuracy (ca. 1% error) in unbuffered media, benchmarked by a commercial glass pH meter. This is the first detailed study on the v application of the economical and scalable technology in pH sensing in unbuffered environment. Chapter 5 presents a unique design of electrochemical pH sensors, free from the need to use a glass reference electrode. This design integrates a pH indicator and an internal reference electrode. Different designs of ferrocene screen-printed electrodes were tested as the internal reference electrode. The nafion-coated ferrocene screen-printed electrode showed stable peak potential in a wide pH range (pH 1 - 12) with good durability (stable in 500+ cycles of test). It was then cross connected with an alizarin electrode, forming the pH sensor free from a glass reference electrode. Chapter 6 describes novel designs of hydrodynamic pH sensors. The design of a microfluidic pH sensor modified by poly-sodium salicylate was firstly demonstrated. The sensor showed a Nernstian response in a wide pH range and, in hydrodynamic conditions, provided improved accuracy in unbuffered media compared to the stagnant state. For more convenient measurements, a novel rocking disc electrode was studied for pH sensing, modified with alizarin and poly-salicylic acid as pH indicators. The electrodes modified by both chemicals showed a Nernstian response in buffered media and the highest accuracy in unbuffered media was reached at 50 rpm.

Made available in DSpace on 2014-06-12T15:51:13Z (GMT). No. of bitstreams: 2 arquivo1504_1.pdf: 791063 bytes, checksum: 4a11c48c67eb0f30d0a7814f389f14a4 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2009 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A necessidade de métodos mais versáteis para a mensuração e monitoramento dos níveis séricos de lipídios tem estimulado a produção de uma grande variedade de novos métodos analíticos. O presente trabalho mostra o desenvolvimento de um biossensor monoenzimático para detecção de triglicerídeos empregando a tecnologia de Screenprinting através da qual, foram impressos os eletrodos de referência (Ag/AgCl) e o de trabalho contendo uma mistura de carbono e quitosana. A lipase foi imobilizada por adsorção no eletrodo de trabalho. A lipase solúvel, usando pNPM, apresentou pH ótimo de 8 e temperatura ótima de 32,5°C, mantendo cerca de 78,5% da atividade máxima a 25°C (temperatura operacional do biossensor). O Km e Vmáx para a lipase solúvel em relação ao pNPM foram de 0,95 mM e 25,51 U/mg proteína, respectivamente. No biossensor desenvolvido com apenas lipase imobilizada, usando trioleína como substrato, foram de 0,148 mM e 262,21 &#956;A/s e 0,304 mM e 85,07 &#956;A/s para a lipase solúvel e TIP sem enzima. Os resultados mostraram linearidade nas respostas de correntes para trioleína (0,25mM 2mM), atestando a viabilidade do biossensor desenvolvido, utilizando unicamente a lipase imobilizada na superfície do eletrodo de trabalho, podendo ser empregado eficientemente para a detecção de triglicerídeos

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Sight is the most important of our five senses. It allows us to navigate our environment, find food and avoid danger. Sight can be used to accurately render a drawing or to recognize nuance in a form. It can also be used in more dynamic ways to parse the complicated social systems and customs that build our societies. Despite all that we can see, we are inundated with what we cannot. This inability to see can be categorized into two subdivisions: items that possess characteristics that are beyond our eye's physical capacity of perception (e.g. microscopic objects or electromagnetic radiation) and items and situations whose exact presence goes unnoticed due to our mind's conditioning from repeated exposure (e.g. glass in a window frame or halftone dots that form a printed picture). Through the use of special instruments or awareness raising techniques these invisible objects can be brought to light. Artists and their art have often played important roles in society by revealing things that go unnoticed and making them plain to see for all. These revelations can be as simple as capturing the beauty of a natural landscape or as controversial as portraying the impact of religion, gender or oppression in our communities. My most recent set of prints investigate "seeing the unseen" by meditating on the minutiae and microscopic organisms that permeate our surroundings yet escape our attention. By utilizing handmade paper's tactile qualities, juxtaposing seemingly dissimilar objects and the use of bold and often times unnatural color, I have attempted to create a space where items of different scales can exist side by side so we can revel in their wonder, discover visual similarities between objects and plainly see them with our own eyes.

Due to the increased awareness of living and industrial safety, carbon monoxide detectors must be geared towards better portability and sensitivity. Metal oxide semiconductor sensors should possess advantages such as heat and corrosion resistance, low cost materials, and ease of miniaturization. This thesis applied ball milled and powdered ZnO and SnO2 to manufacture into paste, then used the screen printing method deposited ZnO and SnO2 paste film and silver electrode on glass substrate. The influence on sensing film materials, temperature, time of heat treatment, and temperature of measurement was investigated. The samples were fabricated and measured by setting up self-measurement apparatus. The data was analyzed the changes of resistance under different air and carbon monoxide environments. This is followed by analysis of both surface topography and microstructure of the sensing film under OM and SEM. Experiment reveals that samples under different annealing process yield different surface morphology and micro structure while at the beginning of the heat treatment, epoxy evaporates from the sample brought about porous structure. Annealing at higher temperature sample will have more rough surface and better sensitivity in detecting carbon monoxide. After epoxy removed, heat treatment mechanism is then switched to sinter ZnO and SnO2 powders. the longer the samples are sintered, the lower the sensitive. Sensing films composited with ZnO and SnO2 will have better carbon monoxide sensitivity at 300oC but its sensitivity decays at a faster rate than samples working at 250 oC despite the slightly weaker sensitivity. Sensing films with pure ZnO will have higher sensitivity compared to pure SnO2 one. With the increase of SnO2 proportion, carbon monoxide sensitivities of detectors decreases, however, its life time can be improve significantly.

A Simple way to improve solar cell efficiency is to enhance the absorption of light and reduce the shading losses. One of the main objectives for the photovoltaic roadmap is the reduction of metalized area on the front side of solar cell by fin lines. Industrial solar cell production uses screen-printing of metal pastes with a limit in line width of 70-80 μm. This paper will show a combination of the technique of laser grooved buried contact (LGBC) and Screen-printing is able to improve in fine lines and higher aspect ratio. Laser grooving is a technique to bury the contact into the surface of silicon wafer. Metallization is normally done with electroless or electrolytic plating method, which a high cost. To decrease the relative cost, more complex manufacturing process was needed, therefore in this project the standard process of buried contact solar cells has been optimized in order to gain a laser grooved buried contact solar cell concept with less processing steps. The laser scribing process is set at the first step on raw mono-crystalline silicon wafer. And then the texturing etch; phosphorus diffusion and SiNx passivation process was needed once. While simultaneously optimizing the laser scribing process did to get better results on screen-printing process with fewer difficulties to fill the laser groove. This project has been done to make the whole production of buried contact solar cell with fewer steps and could present a cost effective opportunity to solar cell industries. / <p>In collaboration with Institute for Photovoltaics <strong><em>IPV</em></strong>, University of Stuttgart.</p>

The subject of this these is a preparation and printing of upconversion marks that have been printed by two printing techniques, namely screen printing and pad printing. The makrs were designed to visualize another chemical code identifiable by instrumentation. The impact of chemical code components on the fluorescence intensity of upconversion marks and the impact of individual components on printability and print sustainability were studied. The upconversion pigment was excited by NIR laser.