Microfluidics have been created to acquire, operate, and process complex fluids in extremely tiny volumes with high efficiency and high speed, and without the requirement for an experienced operator. In addition, microfluidic systems also enable miniaturization and incorporation of different complex functions, which can help bring intricate diagnostic tools out of the laboratories. Ideally, these systems should be inexpensive, precise, reliable, robust, and well-suited to the medical diagnostic systems. Most of the microfluidic devices reported previously were based on devices made of polydimethylsiloxane (PDMS). PDMS is a material that dissolves in many common organic solvents. Meanwhile, it is also prone to absorb small molecules like the proteins, which is detrimental to a stable and reliable result. Current work focuses on bioassays that are badly needed in our life and these bioassays are addressed based on microfluidic platform with different materials. The translation of microfluidic technology into large scale implementations highly relies on new materials that address the limitations of PDMS. Firstly, we fabricated two different microfluidic platforms for rapid antimicrobial susceptibility testing (AST). One was made of hydrogel, and the bacterial cells were cultured on the top of the device; the other was of polypropylene (PP), and bacterial cells were cultured inside the microchannels. Meanwhile, we developed a novel "barcode" sensor, a microscope-free method for cell accumulation and cell counting, as the downstream of the PP-based chips. As a result, AST can be accomplished simply through an application on a mobile phone rather than using an expensive and sophisticated microscope. Secondly, we presented a self-contained paper-based system for lead(II) ion detection based on G-quadruplex-based luminescence switch-on assay, comprising a novel type of paper-based chip and a matching portable device. Different from the reported paper-based devices, the paper substrate we chose was art paper, which is used for printing magazines. This type of paper could prevent the absorption of liquid into the paper matrix and hold the liquid in place for a period of time; and it could also be used for temporary liquid containing like a plastic substrate (such as polypropylene (PP) and polystyrene (PS)), but the surface of the paper is inherently hydrophilic. In such a design, liquid drops are suspended on the surface of the device in designed reservoirs, rather than absorbed into the paper; when the chip is tilted, the liquid drops will move to other reservoirs according to the guidance of channels defined on the surface. To differentiate it from reported μPAD devices that are fabricated with water-permeable paper, we name this new type of paper-based devices suspending-droplet mode paper-based microfluidic devices (SD-μPAD). Different from the conventional μPADs that use capillary force to drive liquid, our SD-μPADs uses wetting and gravity as driving force. To fabricate the superhydrophobic pattern on the paper device, we developed a new microcontact printing-based method to produce inexpensive and precisely patterned superhydrophobic coating on paper. The coating material is poly(dimethylsiloxane) (PDMS), a hydrophobic and transparent silicone that has long been used for fabricating microfluidic devices. Importantly, the negative-relief stamp we used is made of Teflon, a non-stick polymer, so that the PDMS-coated paper could be peeled from the stamp flawlessly. After such fabrication process, the stamped area of the paper is coated with a textured PDMS layer that is decorated with arrays of micropillars, which could provide superhydrophobic effect and most effectively hold the droplets in place; the remaining area of the paper is still hydrophilic. As a demonstration of this new design, we developed a method using the reaction characteristics of iridium(III) complex for rapid, onsite detection of lead(II) ions in liquid samples. As the reagents have already been loaded onto the paper device during fabrication, the only reagent the users need to add is water. Because of the large Stokes shift of the iridium(III) complex probe, inexpensive optical filters can be employed, and we were able to make an inexpensive, battery-powered compact device for routine portable detection using a smartphone as a detector, allowing the rapid analysis and interpretation of results on site as well as the automatic dissemination of data to professional institutes, including tests even in poor rural areas in developing countries. Thirdly, we upgraded our suspending-droplet mode paper-based microfluidic device (SD-μPAD), which is used for the detection of lead(II) ions in liquid solution. The reason is that our paper-based SD chips are not suitable for long reaction process (> 20 min) detection of biomolecules due to the potential permeation and contaminating problems of art papers. Hence, we chose polypropylene (PP), a hydrophobic, cheap, and thermal stable material (< 110°C), as the material for the fabrication of the SD microfluidic chip. We established a convenient, low-cost, portable and reliable platform for monitoring VEGF165 accurately, which can be applied for point-of-care (POC) testing. In this project, we also employed the label-free oligonucleotide-based luminescence switch-on assay on the microfluidic platform, which possesses the advantages of high sensitivity and high selectivity. Based on the detection of VEGF165 in a three-step reaction process, we adopted a new design for the droplet transfer throughout the channels. This design could migrate the droplet through the chambers via controlling the orientation of the chip, which systematically combined the superhydrophobic force of the coating, the gravity of the droplet and the surface tension between PP and droplet. Therefore, traditional micro pump could be avoided and the total cost for the device could be substantially reduced. In addition, we developed an automatic, matched and portable device for the detection of VEGF165, which assembled by a rotatable chip holder, a UV lamp, a filter, and a camera. Finally, we developed a new whole Teflon membrane-based chip for the aptamer screening. Our article "Whole-Teflon microfluidic chips" introduced the fabrication of a microfluidic device entirely using Teflon materials, one group of the most inert materials in the world. It was a successful and representative introduction of new materials into the fabrication of microfluidic devices, which show dramatically greater anti-fouling performance. However, even such device was inadequate for current purpose, as it is rigid and lacks convenient valve control functions for particle suspensions used in systematic evolution of ligands by exponential enrichment (SELEX). For this project, we propose a SMART screening strategy based on a highly integrated microfluidic chip. This new type of whole-Teflon devices, which are made of flexible Teflon membranes, offering convenient valving control for the whole SELEX process to be performed on chip and fulfilling the anti-fouling requirement in the meantime. The SELEX cycles including positive and negative selections could be automatically performed inside tiny-size microchambers on a microchip, and the enrichment is real-time monitored. The selection cycles would be ended after the resulted signal of the aptamers with high specificity reached a plateau, or no target aptamer is captured after a number of cycles of enrichment. Owning to the antifouling property of the chip materials, the loss of the sample is tremendously reduced. The SMART platform therefore is not only free of complicated manual operations, but also high-yield and well reproducible over conventional methods

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

Micro-electro-mechanical Systems (MEMS) technology has revolutionized the micro/nano world by making micro/nano devices feasible. These devices allow more exploration and understanding of the micro/nano world. In this dissertation, we will discuss the measurement of wall shear stress in an integrated microfluidic system built by MEMS technology. Specifically, carbon nanotubes (CNTs) were used as the sensing element for gas-flow shear stress measurement in this work. CNTs have already been proven to have an excellent sensing response to temperature, pressure, and alcohol vapour. Based on the thermal sensing response of CNTs, the sensor was designed to operate using convective heat transfer principles in fluid flow. Dielectrophretic manipulation was used to batch fabricate CNTs on a PMMA substrate. The CNT sensor was then integrated into a PMMA microchannel, which was fabricated by a rapid prototyping technique using moulding/hot-embossing processes. The sensor responded to impinging flow as well as gas-flow shear stress. The sensor activation power was found to be linearly related to the 1/3 exponential power of the wall shear stress. With the measurements of an array of sensors, the flow profile of a microchannel with various types of flow could be studied. Compared with the conventional polysilicon sensor, the CNT sensor has the advantage of small dimensions, i.e. a greater spatial resolution for fluidic measurements, and low power consumption, i.e. it consumes &sim;1,000 times less power than polysilicon sensors. Therefore, CNT sensors have a great potential to serve as an alternative to silicon-based sensors. / Chow, Wing Yin Winnie. / Adviser: Wen J. Li. / Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3743. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 105-110). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

Chen, Qiulan. / "November 2010." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 140-152). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Fang, Caihong = 基於表面等離子體基元的微流芯片光熱技术和金納米棒-納米球二聚體中的表面等離子體基元共振耦合 / 房彩虹. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references. / Abstracts in English and Chinese. / Fang, Caihong = Ji yu biao mian deng li zi ti ji yuan de wei liu xin pian guang re ji shu he jin na mi bang-na mi qiu er ju ti zhong de biao mian deng li zi ti ji yuan gong zhen ou he / Fang Caihong. / Abstract --- p.i / 摘要 --- p.iv / Acknowledgement --- p.vi / Table of Contents --- p.viii / List of Figures --- p.x / Chapter 1. --- Introduction --- p.1 / Chapter 1.1 --- Temperature Control on Microfluidic Chips --- p.2 / Chapter 1.1.1 --- Introduction to Microfluidics --- p.2 / Chapter 1.1.2 --- Temperature Control on Microfluidic Systems and Its Applications --- p.5 / Chapter 1.1.2.1 --- Heating Applications on Microfluidic Chips --- p.5 / Chapter 1.1.2.2 --- Heating/Cooling Methods in Microfluidic Systems --- p.7 / Chapter 1.1.2.3 --- Temperature Measurements in Microfluidic Systems --- p.10 / Chapter 1.2 --- Plasmonic Properties of Noble Metal Nanocrystals --- p.14 / Chapter 1.2.1 --- Localized Surface Plasmon Resonances of Noble Metal Nanocrystals --- p.15 / Chapter 1.2.2 --- Photothermal Conversion of Gold Nanocrystals --- p.19 / Chapter 1.2.3 --- Plasmon Coupling in Gold Nanocrystals --- p.21 / Chapter 1.3 --- Motivation and Outline of the Thesis --- p.23 / References --- p.24 / Chapter 2. --- Growth of Gold Nanocrystals and Characterization Techniques --- p.33 / Chapter 2.1 --- Growth of Au Nanocrystals Samples --- p.33 / Chapter 2.2 --- Characterization Techniques --- p.36 / References --- p.40 / Chapter 3 --- Plasmonic Heating Using Gold Nanorod-Embedded poly(dimethylsiIoxane --- p.43 / Chapter 3.1 --- Embedding Gold Nanorods with Varying Plasmon Resonance Wavelengths into Poly(dimcthylsiloxanc) (PDMS) --- p.43 / Chapter 3.2 --- Plasmonic Heating using Gold Nanorod-Embedded PDMS --- p.54 / Chapter 3.2.1 --- Photothermal Conversion of the Gold Nanorod-Embedded PDMS --- p.54 / Chapter 3.2.2 --- Temperature Measurements Using Rhodaminc B --- p.56 / Chapter 3.2.3 --- Plasmonic Heating and Temperature Measurements on Microfluidic Chips --- p.60 / Chapter 3.2.4 --- Flow Switching Based on the Gold Nanorod-Embedded-PDMS Microfluidic Chips --- p.63 / Chapter 3.3 --- Summary --- p.67 / References --- p.69 / Chapter 4 --- Surface Plasmon Coupling in Gold Nanorod-Nanosphere Heterodimers --- p.73 / Chapter 4.1 --- Preparation of Gold Nanorod-Nanosphere Heterodimers --- p.74 / Chapter 4.2 --- Plasmon Coupling in Gold Nanorod-Nanosphere Heterodimers --- p.77 / Chapter 4.2.1 --- Experimental Results --- p.77 / Chapter 4.2.2 --- Electrodynamic Calculations --- p.82 / Chapter 4.3 --- Summary --- p.89 / References --- p.90 / Chapter 5 --- Summary and Conclusion --- p.93 / Chapter 6 --- Curriculum Vitae --- p.95

Droplet microfluidics generates and manipulates microdroplets in microfluidic devices at high manufacturing efficiency and controllability. Microdroplets have proven effective in biomedical applications such as single-cell analysis, DNA sequencing, protein partitioning and drug delivery. Conventionally, a series of aqueous microdroplets containing biosamples is generated and controlled in an oil environment. One of the critical challenges in this system is that recovery of the aqueous samples from the oil phase is very difficult and often requires expensive and cumbersome post-processing. Also, the low Reynolds (Re) number characteristic of this system results in low throughput of droplet generation. To circumvent challenges and fully utilize microdroplets for practical clinical applications, this research aims to unpack the fundamental physics that governs droplet generation in oil-free systems including an aqueous two-phase system (ATPS) and a high inertial liquid-gas system. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

Graduation date: 2005

A two-dimensional model was developed to predict concentration profiles from passive, laminar mixing of concentration layers formed in a fractal-like merging channel network. Both flat and parabolic velocity profiles were used in the model. A physical experiment was used to confirm the results of the model. Concentration profiles were acquired in the channels using laser induced fluorescence. The degree of mixing was defined and used to quantify the mixing in the test section. Although the results of the experiment follow the trend predicted by the two-dimensional model, the model under predicts the results of the experiment. A three-dimensional CFD model of the flow field in the channel network was used to explain the discrepancies between the two-dimensional model and the experiment. For the channel network considered, the degree of mixing is a function of Peclet number. The effect of geometry on the degree of mixing is investigated using the two-dimensional model by varying the flow length, the width of the inlet channels, and the number of branching levels. A non-dimensional parameter is defined and used to predict an optimum number of branching levels to maximize mixing for a fixed inlet channel width, total length, and channel depth. / Graduation date: 2003

Abstract A new technique for bonding of polymer micro-fluidic devices has been developed. This method can easily bond biochips with complex flow patterns and metal layer. Above all, using a patterned glass, the micro-channel structures on Poly-Methyl Meth-Acrylate (PMMA) substrates were generated by one-step hot embossing procedure. In contrast with the traditional thermal bonding, this paper presents low-temperature and low-pressure packaging for polymer micro-fluidic platforms. Furthermore, the disposable plastic biochip has successfully been tested by the measurement of tensile strength and surface roughness. This paper also reports details of the passive and active micro-mixers. According to experimental and numerical investigations, the mixing performance of passive micro-mixers is expectably to be found. In addition, to quantify the mixing concentration distribution in the micro-channel, it has been demonstrated by launching the image analysis programs. The bonding efficiency of the solvent is twenty four times as strong as thermal bonding efficiency.

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