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Dong Lei. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 75-80). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Introduction to dielectrophoresis --- p.1 / Chapter 1.2 --- Overview of recent works on dielectrophoresis --- p.2 / Chapter 1.3 --- Objectives of the thesis --- p.3 / Chapter 2 --- Dielectrophoresis of homogeneous dielectric spheres in suspen- sions --- p.6 / Chapter 2.1 --- Multiple image method for a pair of homogeneous colloidal par- ticles --- p.7 / Chapter 2.1.1 --- Derivation of the dipole factor --- p.8 / Chapter 2.1.2 --- DEP force for a pair of dielectric spheres --- p.10 / Chapter 2.1.3 --- Multiple image method for the dipole factor of a pair of approaching dielectric spheres --- p.13 / Chapter 2.2 --- Spectral representation and the DEP dispersion spectrum --- p.14 / Chapter 2.3 --- Numerical results --- p.17 / Chapter 2.4 --- Discussion and Conclusion --- p.21 / Chapter 3 --- Electro-orientation of colloidal suspensions --- p.24 / Chapter 3.1 --- Turn-over frequency in electro-orientation --- p.25 / Chapter 3.2 --- Force between a pair of polarized spheres --- p.30 / Chapter 3.3 --- Many-body effects --- p.34 / Chapter 3.4 --- Multipole force due to an intrinsic dispersion --- p.36 / Chapter 3.5 --- Discussion and Conclusion --- p.40 / Chapter 4 --- Exact solutions for graded dielectric spheres in suspensions --- p.42 / Chapter 4.1 --- Exact solutions for the dipole factor --- p.43 / Chapter 4.1.1 --- Exact solution for a power-law profile --- p.46 / Chapter 4.1.2 --- Exact solution for a linear profile with a small slope --- p.48 / Chapter 4.1.3 --- Exact solution of dipole factor for coated microparticles . --- p.50 / Chapter 4.2 --- Comparison between the first-principle approach and other methods --- p.54 / Chapter 4.2.1 --- Comparison with the differential effective dipole approx- imation --- p.55 / Chapter 4.2.2 --- Comparison with the variational approach --- p.56 / Chapter 4.3 --- Effective dielectric constant in the cellular model --- p.59 / Chapter 4.4 --- Discussion and Conclusion --- p.62 / Chapter 5 --- Dielectrophoresis of graded dielectric spheres in suspensions --- p.64 / Chapter 5.1 --- Dielectric response of an isolated graded sphere --- p.66 / Chapter 5.2 --- Dielectric response of a pair of touching graded spheres --- p.69 / Chapter 5.3 --- Discussion and Conclusion --- p.71 / Chapter 6 --- Conclusion --- p.73 / Bibliography --- p.75

Polystyrene spheres, suspended in deionized water, flowing in a microfluidic channel are actuated using a non-uniform electric field, with the final goal of determining the dielectrophoretic (DEP) force spectra of the particles. Particle height changes are detected by measuring the capacitance of set of electrodes at high frequency (1.58 GHz). Two sets of DEP experiments are analyzed for applied DEP signals ranging in frequency from 50 kHz to 10 MHz. For one experiment, a simulated mapping is found to determine the Clausius-Mossotti factor, a frequency dependent term in the DEP force equation, for each particle in the data set. Remaining experiments are analyzed by plotting the normalized height change, a measure of the relative change in height of each particle as an indication of the DEP force.

Polystyrene spheres, suspended in deionized water, flowing in a microfluidic channel are actuated using a non-uniform electric field, with the final goal of determining the dielectrophoretic (DEP) force spectra of the particles. Particle height changes are detected by measuring the capacitance of set of electrodes at high frequency (1.58 GHz). Two sets of DEP experiments are analyzed for applied DEP signals ranging in frequency from 50 kHz to 10 MHz. For one experiment, a simulated mapping is found to determine the Clausius-Mossotti factor, a frequency dependent term in the DEP force equation, for each particle in the data set. Remaining experiments are analyzed by plotting the normalized height change, a measure of the relative change in height of each particle as an indication of the DEP force.

Medical lab work, such as blood testing, will one day be near instantaneous and inexpensive via capabilities enabled by the fast growing world of microtechnology. In this research study, sorting and separation of different ABO blood types have been investigated by applying alternating and direct electric fields using class=SpellE>dielectrophoresis in microdevices. Poly(dimethylsiloxane) (PDMS) microdevices, fabricated by standard photolithography techniques have been used. Embedded perpendicular platinum (Pt) electrodes to generate forces in AC dielectrophoresis were used to successfully distinguish positive ABO blood types, with O+ distinguishable from other blood types at >95% confidence. This is an important foundation for exploring DC dielectrophoretic sorting of blood types. The expansion of red blood cell sorting employing direct current insulative class=SpellE>dielectrophoresis (DC-iDEP) is novel. Here Pt electrodes were remotely situated in the inlet and outlet ports of the microdevice and an insulating obstacle generates the required dielectrophoretic force. The presence of ABO antigens on the red blood cell were found to affect the class=SpellE>dielectrophoretic deflection around the insulating obstacle thus sorting cells by type. To optimize the placement of insulating obstacle in the microchannel, COMSOL Multiphysics® simulations were performed. Microdevice dimensions were optimized by evaluating the behaviors of fluorescent polystyrene particles of three different sizes roughly corresponding to the three main components of blood: platelets (2-4 µm), erythrocytes (6-8 µm) and leukocytes (10-15 µm). This work provided the operating conditions for successfully performing size dependent blood cell insulator based DC dielectrophoresis in PDMS microdevices. In subsequent studies, the optimized microdevice geometry was then used for continuous separation of erythrocytes. The class=SpellE>microdevice design enabled erythrocyte collection into specific channels based on the cell’s deflection from the high field density region of the obstacle. The channel with the highest concentration of cells is indicative of the ABO blood type of the sample. DC resistance measurement system for quantification of erythrocytes was developed with single PDMS class=SpellE>microchannel system to be integrated with the DC- class=SpellE>iDEP device developed in this research. This lab-on-a-chip technology application could be applied to emergency situations and naturalcalamities for accurate, fast, and portable blood typing with minimal error.

Dielectrophoresis (DEP) is a term which describes the motion of polarisable particles induced by a non-uniform electric field. It has been the subject of research into a variety of fields including nanoassembly, particle filtration and biomedicine. The application of DEP to the latter has gained significant interest in recent years, driven by the development of microfluidic “Lab-on-a-chip” devices designed to perform sophisticated biochemical processes. It provides the ability to characterise and selectively manipulate cells based on their distinct dielectric properties in a manner which is non-invasive and label free, by using electrodes which can be readily integrated with microfluidic channels. Under appropriate conditions a biological cell will experience a DEP force directing it either towards or away from concentrations in the electric field. At a so-called “crossover frequency” the cell is effectively invisible to the field resulting in no DEP force, a response typically observed in the 1 kHz to 1 MHz range. Its value is a function of cell membrane dielectric properties and has been the subject of research directed at devices capable of using it to both characterise and sort cells. The aim of this work was to investigate the behaviour of a higher frequency crossover referred to as fxo2, predicted to occur in the 1 MHz to 1 GHz range. At these frequencies the electric field is expected to penetrate the cell membrane and behave as a function of intracellular dielectric properties. Standard lithography techniques have been used to fabricate electrodes carefully designed to operate at these frequencies. The existence of fxo2 was then confirmed in murine myeloma cells, in good agreement with dielectric models derived from impedance spectroscopy. A temperature dependent decrease in its value was observed with respect to the time that cells were suspended in a DEP solution. This decrease is consistent with previous studies which indicated an efflux of intracellular ions under similar conditions. An analytical derivation of fxo2 demonstrates its direct proportionality to intracellular conductivity. Direct control of the crossover was achieved by using osmotic stress to dilute the intracellular compartment and thereby alter its conductivity. By using a fluorophore which selectively binds to potassium, a strong relationship has been demonstrated between the value of fxo2 and the concentration of intracellular potassium. Measurements of fxo2 for an unfed culture demonstrated a correlation with viability and subtle shifts in its distribution were caused by the early stages of chemically induced apoptosis.

Chau, Long Ho. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 91-97). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese.

Leung, Siu Ling. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 60-62). / Abstracts in English and Chinese. / Table of Contents / ACKNOWLEDGEMENT --- p.4 / List of Figures --- p.8 / Chapter 1. --- Introduction --- p.11 / Chapter 1.1 --- Background --- p.11 / Chapter 1.2 --- Project Objective --- p.12 / Chapter 1.3 --- Organization of the Thesis --- p.13 / Chapter 2. --- Literature Review --- p.14 / Chapter 2.1 --- Overview of the Colloidal Gold --- p.14 / Chapter 2.2 --- Dielectrophoresis (DEP) --- p.14 / Chapter 2.2.1 --- CM factor of Single Shell Model --- p.16 / Chapter 2.3 --- Double Layer and AC Electroosmosis --- p.18 / Chapter 2.3.1 --- Double Layer --- p.18 / Chapter 2.3.2 --- AC Electroosmosis --- p.19 / Chapter 2.4 --- Electrothermal Body Force --- p.19 / Chapter 3. --- Theoretical Analysis of DEP Manipulation --- p.21 / Chapter 3.1 --- Particle Manipulation by DEP Force --- p.21 / Chapter 3.2 --- Electric Induced Fluid Flow --- p.22 / Chapter 3.2.1 --- Double Layer and AC Electroosmosis --- p.22 / Chapter 3.2.2 --- Electrothermal Body Force --- p.24 / Chapter 3.3 --- DEP Manipulation against Fluid Flow --- p.25 / Chapter 4. --- Fabrication of AuNP based Sensors --- p.28 / Chapter 4.1 --- Fabrication of Arrays of Microelectrodes --- p.28 / Chapter 4.2 --- Formation of AuNP based Pearl Chains across Microelectrodes --- p.30 / Chapter 4.2.1 --- Formation Circuit --- p.30 / Chapter 4.2.2 --- Microspotting System --- p.31 / Chapter 4.2.3 --- Results and Discussion --- p.32 / Chapter 5. --- Exploring the Critical Parameters in Controlling AuNP Pearl Chain Formation (PCF) --- p.35 / Chapter 5.1 --- Exploring the Optimum Frequencies --- p.35 / Chapter 5.1.1 --- Analyzing the observation of pearl chain formation under specific frequency ranges --- p.36 / Chapter 5.1.2 --- Conclusion on the Optimum Frequency for PCF --- p.40 / Chapter 5.2 --- Exploring the Optimum Voltages --- p.41 / Chapter 5.3 --- Influence of the Particle size on the Formation Rate --- p.43 / Chapter 6. --- Characteristics of the AuNP based Pearl Chain --- p.44 / Chapter 6.1 --- I-V Characteristics --- p.44 / Chapter 6.2 --- Thermal Sensitivities --- p.45 / Chapter 7. --- Application of the AuNP based Sensor - Airflow Sensor --- p.48 / Chapter 7.1 --- Experimental Setup --- p.48 / Chapter 7.2 --- Experimental Results --- p.49 / Chapter 7.2.1 --- Sensor Response to Air --- p.49 / Chapter 7.2.2 --- Sensor Response to Nitrogen Gas --- p.50 / Chapter 7.2.3 --- Control Experiment --- p.51 / Chapter 7.3 --- Discussions --- p.53 / Chapter 7.3.1 --- Relationship between the Measured Electric Response and Temperature --- p.54 / Chapter 7.3.2 --- Pressure-Temperature Relationship of the Sensor --- p.55 / Chapter 8. --- Conclusion --- p.57 / Chapter 9. --- Future Work --- p.58 / Chapter 9.1 --- DEP Manipulation of 2nm diameter gold nanoparticles --- p.58 / References --- p.60 / List of Publications --- p.63 / APPENDIX-I / The Clausius-Mossoti (CM) Factor --- p.64 / Chapter I-1 --- The CM factor of homogeneous dielectric spheres --- p.64 / Chapter I-2 --- The CM factor of a single shell sphere --- p.65 / APPENPIX-II / Estimating the Minimum Voltage for Electrolysis by the Nernst Equation [39] --- p.67 / Chapter II-l --- Gibb´ةs Free Energy and the Nernst Equation --- p.67 / Chapter II-2 --- Minimum Voltage Required for Electrolysis of Water with Different pH --- p.67 / Appendix-III / Temperature-Voltage Relationship of the K-type Thermocouple [40] --- p.69 / Appendix-IV / Mathlab Program --- p.70 / Chapter IV-1. --- Fluid velocity induced by AC electroosmosis --- p.70 / Chapter IV-2. --- Voltage drop across the double layer --- p.70 / Chapter IV-3. --- Fluid velocity induced by electrothermal force --- p.71 / Chapter IV-4. --- CM Factor Simulation --- p.72 / Chapter IV-5. --- Particle velocity induced by DEP force --- p.73

Every environment of the biosphere supports a particular mix of microorganisms called a microbiome. These diverse microbial communities play critical roles in the health of ecosystems and in higher organisms, including humans. Disruption or translocation of microbiomes may cause lethal infections, contaminate food and drug supplies, and adversely impact industrial activities. Microbiome detection and molecular characterization have emerged as priorities in many fields. Available methods cannot quickly and efficiently extract rare microorganisms in real specimens. Therefore, microbial detection and analysis require long incubation periods or the use of technically challenging molecular biotechnologies. These strategies are impractical in situations requiring immediate intervention. The intrinsic electric and dielectric properties of microbes permit their isolation by the phenomenon of dielectrophoresis in microfluidic devices. These microsystems have the potential to enhance microbial analysis but are plagued by low processing rates and the inability to interface with biological specimens containing high levels of interfering cells and debris. In this study, a method was created to discriminate between target microbes and undesired cells on the basis of their differential susceptibility to permeabilizing agents that altered cell dielectrophoretic responses. Fabrication techniques were developed to manufacture high-aspect ratio microfluidic channels that allowed the physical forces of gravity, diffusion and dielectrophoresis to be exploited to control cell positions over microscale distances normal to a Poiseuille flow gradient. Because the positioning effects were exploited in only one dimension, the other two dimensions of the channels could be scaled up to create large channel cross-sectional areas that supported rapid specimen processing rates while maintaining high separation efficiencies expected for the microscale effects. These strategies were applied in various ways to isolate microbes from whole blood, platelets, stool, saliva, and skin specimens. The dielectrophoretic extraction of microbes enabled by this approach was used to enable electrical impedance detection of ~100 bacteria in less than five hours. As a result, important technological barriers that have limited the applicability of dielectrophoresis in clinical and industrial settings were overcome by increasing throughput and addressing sample preparation requirements. These proof-of-concept data demonstrate the potential for accelerating microbial isolation and detection in diagnostics, screening, and microbiome research. / text

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