在不均勻電場下產生的交流電動力是一種非常重要的物理現象，並且非常適合對微流體系統中的微粒子和溶液進行直接操控。微流體中主導的力會根據所加交流電場的參數，如電壓和頻率；以及溶液和微粒子的特性，如導電率和介電常數而改變。 / 這篇論文將會討論在微流體芯片中利用交流電動力的三個生物醫學領域應用範例。第一個例子中，介電電泳被用來擔任集中器的作用，將溶液中DNA附著的碳納米顆粒排列在微電極之間。這種納米材料的性質以及作為傳感器應用的可能性也將被研究。第二個應用著重在微通道中對細胞的操控。試驗過程中觀察到黑色素細胞在正介電電泳力作用下的自旋現象，而不含黑色素的細胞在相同條件下鮮少發生。研究的重點包括產生這種現象的條件和可能原因，以及對細胞旋轉速度的量化和比較。在這基礎上，實驗證實了對原本不含黑色素的細胞實現人為引發自旋現象的可能性。在第三個應用中，交流電熱流被用來輔助電化學生物傳感器的RNA雜交過程從而克服封閉系統生物傳感器的一些缺點，進而實現快速病原檢測。優化后的生物傳感器序列陣列性能非常有競爭力。具體來說，傳感器特異性良好，信噪比提高，檢測限提升。另外，初步臨床樣本檢測證實這種交流電動力輔助下的生物傳感器陣列具有在將來被整合成便攜式醫療檢測儀器從而實現分子生物診斷的潛質。 / AC Electrokinetics is a very important phenomenon in the presence of non-uniform electric fields that is suited for direct manipulation of both particles and bulk fluid in the microfluidic system. Based on the parameters of the applied AC electric field such as voltage and frequency, as well as the properties of solution and the particles, for example, conductivity and permittivity, dominant forces in the microfluidic system may vary. / In this thesis, three examples of utilizing AC Electrokinetics in the microfluidic system for biomedical applications will be discussed. The first application was to use dielectrophoresis as a concentrator to form DNA attached carbon nanoparticles alignment between microelectrodes. The properties of this type of nanomaterial were investigated for further sensing applications. Then, the second example focused on cell manipulation in the microchannel, as self-rotation phenomenon of the pigment cells under positive dielectrophoretic force was observed, while there was no movement for non-pigment cells applied with the same dielectrophoresis parameters. The conditions and possible reasons for this phenomenon were investigated, the cell rotation speed was quantified and compared, based on which, manually induced rotation using non-pigment cells was proved successful. Last but not least, AC Electrothermal effect was utilized to facilitate the hybridization process of electrochemical biosensor arrays to overcome the disadvantages of enclosed sensor system and to further realize rapid pathogen identification. Optimized biosensor arrays showed promising performance including good specificity for a panel of target species, enhanced signal-to-noise ratio and improved limit-of-detection. Furthermore, preliminary clinical sample validation was conducted to confirm the feasibility of using this type of AC Electrokinetically facilitated biosensor arrays for future integration into a point-of-care device for molecular diagnostics. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Ouyang, Mengxing. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 103-110). / Abstract also in Chinese. / List of Figures --- p.ix / List of Tables --- p.xiii / List of Abbreviation --- p.xiv / Chapter I. --- Introduction to AC Electrokinetics --- p.15 / Chapter 1.1. --- AC Electrokinetics --- p.15 / Chapter 1.2. --- Dielectrophoresis --- p.16 / Chapter 1.3. --- AC Electrothermal Flow --- p.17 / Chapter 1.4. --- Advantage of Miniaturized Microfluidic Device --- p.18 / Chapter II. --- DEP Manipulation of CNPs and DNA-CNPs --- p.20 / Chapter 2.1. --- Introduction --- p.20 / Chapter 2.1.1. --- Carbon Nanoparticles and Their Applications --- p.20 / Chapter 2.1.2. --- Fluorescent CNPs and Bio-imaging --- p.21 / Chapter 2.1.3. --- DNA Attached Nanomaterials --- p.23 / Chapter 2.2. --- Preparation of CNPs --- p.24 / Chapter 2.2.1 --- Fabrication Process --- p.24 / Chapter 2.2.2 --- Fluorescence Property --- p.24 / Chapter 2.3. --- DEP Manipulation of CNPs --- p.27 / Chapter 2.3.1. --- CNPs Linkage Formation --- p.27 / Chapter 2.3.2. --- DEP Parameters --- p.28 / Chapter 2.3.3. --- Electrical Stability --- p.30 / Chapter 2.4. --- DEP Manipulation of DNA-attached CNPs --- p.32 / Chapter 2.4.1. --- Preparation of Sensor Chips --- p.32 / Chapter 2.4.2. --- Current-Voltage Characterization --- p.34 / Chapter 2.4.3. --- Stability --- p.35 / Chapter 2.4.4. --- Temperature Dependency --- p.39 / Chapter 2.4.5. --- Humidity Dependency --- p.40 / Chapter 2.5. --- Summary --- p.44 / Chapter III. --- Self-Rotation of Cells in the DEP Field --- p.45 / Chapter 3.1 --- Introduction --- p.45 / Chapter 3.2 --- Preparation of Microfluidic Chips --- p.46 / Chapter 3.2.1 --- Electrode Design --- p.46 / Chapter 3.2.2 --- Fabrication of Microfluidic Chips --- p.47 / Chapter 3.3 --- Cell Rotation Experiments --- p.49 / Chapter 3.3.1 --- Cell Behavior in the Dielectrophoretic Field --- p.49 / Chapter 3.3.2 --- Conditions to Induce Self-Rotation Phenomenon --- p.50 / Chapter 3.3.3 --- Pigment Cells Versus Non-Pigment Cells --- p.54 / Chapter 3.3.4 --- Investigation of Self-Rotation Speed of Pigment Cells --- p.55 / Chapter 3.3.5 --- Self-Rotation of Pigment Cells from Different Passages --- p.60 / Chapter 3.3.6 --- Cell Rotation Speed Calculation Using Algorithm --- p.62 / Chapter 3.3.7 --- Manually Induced Cell Rotation --- p.64 / Chapter 3.4 --- Summary --- p.67 / Chapter IV. --- AC Electrothermal Flow Facilitated Biosensors --- p.68 / Chapter 4.1 --- Introduction --- p.68 / Chapter 4.2 --- Probes and Biosensor Arrays --- p.71 / Chapter 4.2.1 --- Probe Design --- p.71 / Chapter 4.2.2 --- Specificity and Sensitivity of The Enclosed System --- p.71 / Chapter 4.2.3 --- Clinical Urine Sample --- p.73 / Chapter 4.2.4 --- Electrochemical Biosensor Arrays and Their Functionalization --- p.74 / Chapter 4.3 --- Mechanism and Experimental Methods --- p.76 / Chapter 4.3.1 --- Detection Mechanism of 16S rRNA --- p.76 / Chapter 4.3.2 --- Two-Color Fluorescence Thermometry --- p.78 / Chapter 4.3.3 --- Fluorescent Sphere Velocity Measurement --- p.79 / Chapter 4.4 --- Microscale Characterization of the Enclosed System --- p.80 / Chapter 4.4.1 --- Improvement of Washing Process --- p.80 / Chapter 4.4.2 --- Temperature Measurement --- p.80 / Chapter 4.4.3 --- Quantification of ACEK facilitated Mixing --- p.82 / Chapter 4.5 --- Optimization of ACEK Parameters --- p.84 / Chapter 4.5.1 --- Hybridization Duration --- p.84 / Chapter 4.5.2 --- Voltage --- p.85 / Chapter 4.6 --- Performance of a Panel of Target Species --- p.89 / Chapter 4.6.1 --- Limit of Detection --- p.89 / Chapter 4.6.2 --- Specificity --- p.90 / Chapter 4.7 --- Clinical Sample Validation --- p.92 / Chapter 4.8 --- Discussion --- p.94 / Chapter 4.8.1 --- Hybridization Efficiency --- p.94 / Chapter 4.8.2 --- Background Signal --- p.96 / Chapter 4.9 --- Summary --- p.97 / Chapter V. --- Conclusion --- p.98 / Chapter 5.1 --- Nanoparticles Concentration Using DEP --- p.98 / Chapter 5.2 --- Cell Manipulation in the DEP field --- p.100 / Chapter 5.3 --- AC Electrothermal Flow Facilitated Enclosed Biosensors --- p.101 / Bibliography --- p.103

During the last decade, large and costly instruments are being replaced by system based on microfluidic devices. Microfluidic devices hold the promise of combining a small analytical laboratory onto a chip-sized substrate to identify, immobilize, separate, and purify cells, bio-molecules, toxins, and other chemical and biological materials. Compared to conventional instruments, microfluidic devices would perform these tasks faster with higher sensitivity and efficiency, and greater affordability. Dielectrophoresis is one of the enabling technologies for these devices. It exploits the differences in particle dielectric properties to allow manipulation and characterization of particles suspended in a fluidic medium. Particles can be trapped or moved between regions of high or low electric fields due to the polarization effects in non-uniform electric fields. By varying the applied electric field frequency, the magnitude and direction of the dielectrophoretic force on the particle can be controlled. Dielectrophoresis has been successfully demonstrated in the separation, transportation, trapping, and sorting of various biological particles. / Singapore-MIT Alliance (SMA)

Electric field guided assembly of colloids is a new area of research in colloidal science where sub-micrometer particles, or colloids, are assembled using patterned electrodes. The design of these devices is often limited by an inability to characterize accurately forces and fluxes with linearized electrokinetic theory. The research presented in this dissertation describes an application of the finite element method to the nonlinear electrokinetic equations. The finite element model thus developed is then used to describe the nonlinear electrophoretic mobility of a dilute colloidal dispersion, investigate hydrodynamic and electric particle-particle interactions, and characterize particle-surface interactions. The effect of Stern layer conduction on the electrophoretic mobility and dielectric response is included using the generalized dynamic Stern layer model. The electrokinetic force is calculated using the Maxwell stress tensor method rather than the effective dipole method as it is more consistent with nonlinear electrokinetic theory. Significant results of this dissertation demonstrate the effect of nonlinear electrokinetic phenomena and extend the present electrokinetic theory. The calculation of nonlinear electrophoretic mobility of a dilute colloidal dispersion, which is valid for arbitrary particle surface charge or zeta potential, applied (AC) electric field strength, and applied AC electric field frequency. Also, the adsorption isotherm used by the generalized dynamic Stern layer theory is extended to include non-equilibrium reaction kinetics. This results in a model for Stern layer conduction which is valid for frequencies above 1 MHz. The utilization of the Maxwell stress tensor method results in a finite element model which is valid for arbitrary electric field strength and includes the effects of traveling-wave dielectrophoresis a nonlinear electrokinetic phenomena resulting from non-uniform electric field phase.

An alternating current electroosmotic micro pumping device has been designed, experimentally tested and theoretically analyzed using an electrohydrodynamic theoretical model applied to a computer simulation model. The device SP-1 is a microelectrode array which uses the principal of AC electroosmosis (EO), ions driven along microelectrode surfaces by coulomb forces produced by tangential electric fields. These ions, when driven, induce a net fluid motion due to viscous drag forces. Three submerged microelectrode wires were deposited on a substrate using microfabrication techniques such that a square spiral geometry was formed. Device SP-1 received asymmetrically applied AC signals creating a travelling wave of potential and resulted in a net fluid flow across the microelectrode array. Microsphere tracer particles were suspended in ethanol to measure the fluid velocity to determine pumping performance and the experimental operating frequency at which maximum fluid velocity is achieved. The experimental results were reviewed and at an AC signal frequency of 125 Hz, device SP-1 was capable of pumping ethanol at a fluid velocity of approximately 270 μm/s. The experimental results were in good agreement with the theoretical predictions produced using the computer simulation model. In addition, the computer simulation model predicted a similar flow profile to those previously predicted and experimentally observed. Overall, novel micropumping device SP-1 was found to produce a net flow comparable to previously tested devices and a computer simulation framework capable of analyzing future micropump design concepts was developed. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2011-04-01 17:12:02.908

In this thesis, three specific research contributions to the use of non-uniform electric field driven colloidal assembly are described. The first relates to experimental work using dielectrophoretic and electrohydrodynamic forces (electroosmosis) to shape three-dimensional colloidal structures. Formation and stabilization of close-packed three-dimensional structures from colloidal silica was demonstrated, using gelation of pluronic F-127 to preserve medium structure against suspension evaporation. Stabilization of ordered structures was shown to be a significant challenge, with many of the conventional techniques for immobilizing colloidal crystals being ineffective. Secondly, the significance of electrohydrodynamic flows resulting from electric and particle concentration (entropic) gradients during the assembly process was demonstrated using numerical simulations based on a thermodynamic framework. These simulations, as well as experimental validation of assembly and the presence of fluid flows, showed that assuming equilibrium behavior (stationary fluid flow), a common assumption for most modelling work to date in these systems, is inappropriate at all but the most dilute concentration cases. Finally, the relevance of multiparticle effects on electric-field induced phase transitions of dielectric colloids was demonstrated. The effect of multiparticle/multiscattering effects on the suspension permittivity were accounted for using semi-empirical continuum permittivity formulations which have been previously shown to describe a wide variety of solid packing structures, including face-centered cubic and other colloidal crystal structures. It was shown that multiparticle effects have a significant impact on both the coexistence (slow phase separation) and spinodal (fast phase separation) behavior of dielectric suspensions, which has not been demonstrated to date using a continuum framework. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2012-01-30 14:17:23.747

Thesis (Ph.D.)--Drexel University, 2007. / Includes abstract and vita. Includes bibliographical references (leaves 148-150).

Thesis (Ph. D.)--Lehigh University, 2002. / Includes vita. Includes bibliographical references (leaves 151-157).

Thesis (Ph. D.)--University of Washington, 1999. / Vita. Includes bibliographical references (leaves 71-75).

Thesis (M.S.)--California Polytechnic State University, 2009. / Mode of access: Internet. Title from PDF title page; viewed on October 14, 2009. Major professor: David Clague, Ph.D. "Presented to the faculty of California Polytechnic State University, San Luis Obispo." "In partial fulfillment of the requirements for the degree [of] Master of Science in Engineering, with specializations in Biomedical Engineering." "September 2009." Includes bibliographical references (p. 125-127).

We have developed a new biofabrication process in which the precise control of bacterial motion is used to fabricate customizable networks of cellulose nanofibrils. This work describes how the motion of Acetobacter xylinum can be controlled by electric fields while the bacteria simultaneously produce nanocellulose, resulting in networks with aligned fibers. Since the electrolysis of water due to the application of electric fields produces the oxygen in the culture media far from the liquid-air boundary, aerobic cellulose production in 3D structures is readily achievable. Five separate sets of experiments were conducted to demonstrate the assembly of nanocellulose by Acetobacter xylinum in the presence of electric fields in micro and macro environments. This work demonstrates a new concept of bottom up material synthesis by control of a biological assembly process. / Master of Science