京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第19474号 / 理博第4134号 / 新制||理||1595(附属図書館) / 32510 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 荒木 武昭, 教授 佐々 真一, 教授 山本 潤 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

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The influence of microparticles on electroosmotic flow was investigated experimentally and numerically. Experiments were conducted using four different particle types of varying chemical composition, surface charge and polarity. Each particle type was tested at five different volume fractions ranging from 0.001 – 0.025. With a constant applied electric field, positively charged particles enhanced the electroosmotic flow by as much as 850%. The enhancement depended on particle composition, size and concentration. For negatively charged particles, the bulk electroosmotic flow was retarded with the largest reductions being 35%. This occurred for the greatest negative paricle concentration studied. A final experimental study utilizing a single volume fraction and particle type was conducted using microtube inner diameters of 100 – 300 micrometers. It was found that the effective electroosmotic mobility decreases with increasing microtube diameter. A numerical study of microparticle influenced electroosmotic flow was also conducted for positively and negatively charged particles. A Galilean transformation was employed in which the particles were held stationary. A moving wall model was utilized to account for the particle velocity and the wall-induced electroosmotic flow. The particle-induced electroosmotic flow was also accounted for. A range of particle velocities were imposed in order to study the flow physics for a range of potential flows. Scenarios were run for a single tube diameter of 100 micrometers and a single particle diameter of 1.7 micrometers. Volume fractions of 0.001, 0.0075 and 0.025 were tested for both positively and negatively charged particles. At least two particle charges were studied for each volume fraction and polarity. Comparisons of the trends in the numerical model are qualitatively compared with the trends in the experimental data. The numerical and experimental data demonstrated similar trends. For positively charged particles, an increase in volume fraction showed a nonlinear increase in the average bulk flow velocity. For negatively charged particles an increase in volume fraction showed a nonlinear decrease in the average bulk flow velocity.

Doctor of Philosophy / Over 1.9 million new cases of cancer will pop up just this year alone. The prevalence of cancer, however, has not been met with the same magnitude of effective treatments, resulting in over 600,000 deaths in the United States. Before current treatments can be improved and new treatments can be developed, it is critical that we increase our understanding of what drives cancer to be so aggressive and maintain a fighting chance within the body despite our complex immune systems. The severity of cancer is not just a product of the cancer cell itself, but rather the components that make up the cell that define and drive metastatic behaviors and drug resistance. In order to improve diagnoses, prognoses, and treatment planning, the intracellular drivers of the disease must be better understood. Cells, electrical circuits in nature, reflect unique electrical properties dictated by their biophysical composition. These electrical properties can be revealed and exploited to characterize and treat contributors to disease progression. Using electric fields applied in several modalities, this work explores the electrical entities of malignant cell types towards improving in vitro treatment planning and developing a treatment modality cognizant of subcellular drivers. This dissertation details the use of dielectrophoresis and electroporation to detect and treat intracellular changes associated with poor prognosis.

Electrokinetics is a family of effects that induces motion of a liquid or a particle within a liquid in response to an external electric field. Using the intrinsic electrical properties of bacteria and of breast cancer cells, electrokinetics can be used to manipulate these particles for two different types of applications: tissue engineering and breast cancer detection. The first application studied the effects of electric fields on bacteria cells as well as calcium ions to potentially create a meniscus scaffold with hydroxyapatite ends for anchoring. In response to the electric field, calcium ions were able to deposit locally and simultaneously with cellulose growth. Bacteria cells were also studied to determine their response under an AC field. At low frequencies, bacteria demonstrated controlled movement caused by electroosmosis and dielectrophoresis with a net motion caused by a dielectrophoretic force. In the second application, the separation capabilities of different stages of breast cancer cells from the same cell line were tested using contactless dielectrophoretic (cDEP) devices. The electric field gradients in cDEP devices were altered to optimize selectivity and to determine an estimated membrane capacitance for each. From the results, the membrane capacitance of the early to intermediate stages proved to be very similar; however, late stage breast cancer cells have potential in being separated from early and intermediate stages. / Master of Science

AC electrothermal flow (ACEF) is the fluid motion created as a result of Joule heating induced temperature gradients. ACEF is capable of performing major microfluidic operations, such as pumping, mixing, concentration, separation and assay enhancement, and is effective in biological samples with a wide range of electrical conductivity. Here, we report long-range fluid motion induced by ACEF, which creates centimeter-scale vortices. The long-range fluid motion displays a strong voltage dependence and is suppressed in microchannels with a characteristic length below similar to 300 mu m. An extended computational model of ACEF, which considers the effects of the density gradient and temperature-dependent parameters, is developed and compared experimentally by particle image velocimetry. The model captures the essence of ACEF in a wide range of channel dimensions and operating conditions. The combined experimental and computational study reveals the essential roles of buoyancy, temperature rise, and associated changes in material properties in the formation of the long-range fluid motion. Our results provide critical information for the design and modeling of ACEF based microfluidic systems toward various bioanalytical applications. (C) 2016 Elsevier Ltd. All rights reserved.

This research exploits mild sonication in a thin layer electrochemical cell to enhance rates of reaction in systems under voltammetric perturbation. Sound waves propagate through a thin layer of condensed fluid to provide energy to the electrode solution interface in the form of pressure and temperature. The sonic energy provided in three dimensions can be exploited to enhance rates of heterogeneous electron transfer as the energy is harnessed at the two dimensional electrode interface. Enhanced rates of heterogeneous electron transfer are of interest both for fundamental reasons and for exploitation in electrochemical energy systems. The initial pilot studies were directed at demonstrating the impact of acoustic energy on heterogenous electron transfer. Redox couples with different electron transfer rates were evaluated. Whereas compounds with reversible electron transfer kinetics demonstrated little improvement, redox couples such as ferric ion (Fe3+) with slow electron transfer kinetics exhibited an increase in the standard heterogeneous electron transfer rate constant, k0 with an increase in acoustic energy. The reduction of oxygen is a complex four proton, four electron process that is of technological importance. Slow kinetics of the oxygen reduction is a primary loss of efficiency in electrochemical power sources. Much like the ferric ion, oxygen kinetic rats improve. Preliminary studies in the oxidation of methanol demonstrated a sonocatalyic effect in methanol electrolysis that is of particular interest for the development of liquid based fuel cells. Sonication can both clean and destroy surface materials. The cleaning power inherent in sonication improves electrocatalysis and removes deposits and oxides from the electrode surface.

<p>The presence of <i>Escherichia coli</i> in water is an environmental indicator that the water is contaminated with faeces. Approximately, 30% of the world population drink water from sources contaminated with human faeces. Consequently, this percentage comprises of people that are highly vulnerable to <i>Escherichia coli</i> infection. While most strains of <i>Escherichia coli</i> are harmless or maintain a symbiotic relationship with humans, the pathogenic strains are responsible for injurious health effects, such as diarrhoea and kidney failure. The traditional method of detecting <i>Escherichia coli</i> takes about 24 – 48 hours, does not detect viable but non-culturable cells, and requires advanced equipment and great technical skills. Most other available detection techniques lack specificity, as observed with enzyme-based techniques, or are not very sensitive, as observed with most impedance-based techniques with clogged surfaces.</p> <p> </p> <p>As a result of the health effects due to this microorganism and the basic limitations of available detection techniques, there is need for a specific, sensitive and rapid detection technique to ensure a sustained and timely access to <i>E. coli</i>- free water. Therefore, the aim of this research work is to develop a detection technique devoid of the basic limitations of available methods. In this study, the antibody-antigen relationship was taken advantage of to ensure the specificity of the technique is guaranteed. This was achieved using <i>Escherichia coli</i> polyclonal antibodies that target the O and K antigens found in most pathogenic strains. These antibodies were functionalized on carboxyl group modified superparamagnetic fluorescent microparticles immobilized with streptavidin. The sensitivity of the technique was ensured by utilizing the low detection limit feature offered by the use of microfluidic devices. Two microfluidic devices, glass-based and PDMS-based, were fabricated with easily accessible materials. </p> <p> </p> <p>On introducing the sample reagents and test samples into the microfluidic devices, and passing an alternating current frequency through the system, the antibodies specifically isolated the target organisms from the pool of water contaminants and a drop in the device electric potential proportional to the bacteria concentration was observed. The success of this procedure depends on the identification of the alternating current frequency beyond which manipulation of the samples would not be easily carried out. As a result, the flow field analysis of the microparticles was carried out to study the particle behavior by varying the alternating current frequency from 15 kHz – 75 kHz. </p> <p> </p> <p>The optimum frequency observed was 35 kHz. Using the glass-based microfluidic device, the voltage drop observed for the serial dilutions, 10¹ to 10⁶ ranged from 200 mV to 420 mV while that for the serial dilutions, 10^-7 to 10^-1 ranged from 90 mV to 285 mV. To ascertain if a lower detection limit could be obtained, the PDMS-based microfluidic device, with a channel with of 300 µm, was used to analyze the response of the device to 10^-7 to 10^-1<b> </b>serial dilutions. The result ranged from 10 mV to 30 mV respectively. A comparative analysis with the conventional detection method showed that it was able to detect less than 300 <i>Escherichia coli</i> colony-forming units. This result indicates that an optimized PDMS-based microfluidic device with higher resolution microchannel could potential detect tens of bacteria colony-forming units. These results were obtained in about 60 secs of introducing the sample in the device.</p> <p> </p> <p>The rapidity and consistency of the results observed by the continuous increase in voltage drop with increasing concentrations of <i>Escherichia coli</i> indicate that this detection technique has great potential in addressing the time, specificity and sensitivity issues observed with most available detection methods.</p><br>

<p>A literature survey on modelling of the resistance spot welding process has been carried out and some of the more interesting models on this subject have been reviewed in this work. The underlying physics has been studied and a brief explanation of Heat transfer, electrokinetics and metallurgy in a resistance spot welding context have been presented.\nl\hsLastly a state of the art model and a simplified model, with implementation in the FEM software LS-DYNA in mind, have been presented.</p>

Hot microelectrodes are very small electrodes (usually 1 100 µm in diameter), which have a surface temperature much higher than the temperature in the bulk solution. In this work, the heating is achieved by applying an alternating potential of very high frequency (100 MHz 2 GHz) and of high amplitude (up to 2.8 Vrms) to the microelectrode. As a result, very fast (on the order of milliseconds) changes in the temperature of the electrolyte solution surrounding the electrode can be achieved. Due to the size of the heated microelectrodes, the hot zone in solution is small. Therefore, the solution can be easily overheated and temperatures above the boiling point can be reached.<p> The purpose of this research was to investigate and understand the phenomena occurring at ac polarized microelectrodes and to propose new applications of these electrodes. Using both steady-state and fast-scan (10 V/s) cyclic voltammetry measurements, mass transport of redox species has been studied at ac heated microelectrodes. It has been established that the convection at hot-disk microelectrodes is driven primarily by the electrothermal flow of an electrolyte solution. In addition, other effects such as ac dielectrophoresis and Soret (nonisothermal) diffusion are also observed. Numerical simulations have been employed to predict the distribution of temperature in the hot zone, the direction and magnitude of the electrothermal force and the solution flow rate, as well as the voltammetric response of hot-disk microelectrodes. The results of the simulations agree well with the experimental observations. Theoretical findings of this PhD work are very important for the understanding of the fundamentals of high temperature electrochemistry, particularly mass transport. The proposed explanation of the convection mechanism is most likely applicable not only to ac polarized microelectrodes, but also to the microwave heated microelectrodes, since the only difference between these two heating methods is in the way of delivering electrical energy (wired vs. wireless). The results of the studies of Soret diffusion indicate that it contributes significantly to mass transfer of redox species at hot microelectrodes. Taking into account that the magnitude of the Soret effect has been considered negligible by other electrochemists, the results obtained in this work prove the opposite and show that Soret diffusion affects both the faradaic current and the half-wave potential of the redox reaction. Therefore, the Soret effect can not be ignored if working with hot microelectrodes.<p> Hot microelectrodes can have a number of interesting applications. The results of the initial investigations indicate that these electrodes can be successfully used in the arrangement for Scanning Electrochemical Microscopy (such a novel technique is termed Hot-Tip SECM). In addition, the observed dielectrophoretic and electrothermal convection effects can enhance the performance of the electrochemical sensors based on hot microelectrodes. This can lead to the improvement of the detection limits of many biologically important analytes, such as proteins, bacteria and viruses.