Browsing by Subject "Microfluidic"
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Item A microfluidic device for continuous capture and concentration of pathogens from water(2009-05-15) Balasubramanian, Ashwin KumarA microfluidic device, based on electrophoretic transport and electrostatic trapping of charged particles, has been developed for continuous capture and concentration of microorganisms from water. A generic design, utilizing mobility and zeta potential measurements of various microorganisms exposed to different environmental conditions and physiological states, was employed. Water and buffer samples at pH values ranging from 5.2?7.0 were seeded with bacteria (E. coli, Salmonella, and Pseudomonas) and viruses (MS-2 and Echovirus). Negative control and capture experiments were performed simultaneously using two identical devices. Both culture based methods and real-time PCR analysis were utilized to characterize the capture efficiency as a function of time, flowrate, and applied electric field. Based on differences between the capture and negative control data, capture efficiencies of 90% to 99% are reported for E. coli, Salmonella, Pseudomonas, and MS-2, while the capture efficiency for Echovirus was around 75%. Overall, the device exhibits 16.67 fold sample volume reduction within an hour at 6 mL/hr. This results in a concentration factor of 15 at 90% capture efficiency. Direct quantification of capture on the anode of the prototype microfluidic device was also performed by particle tracking using fluorescent microscopy. Based on image processing, the capture data at different locations on the electrode surface is quantified as a function of the wall shear stress at these locations, which is calculated using CFD simulations. Finally, the Faradaic processes in the microchannel due to electrochemical reactions are studied to predict the amount of electrophoresis in the system. Scaling of the device to sample 5 L/hr can be achieved by stacking 835 identical microchannels. Power and wetted volume for the prototype and scaled devices are presented. The device can thus function either as a filtration unit or as a sample concentrator to enable the application of real-time detection sensor technologies. The ability to continuously sample water without chemical additives facilitates the use of this device in drinking water distribution systems. This work constitutes the first step in our development of a continuous, microbial capture and concentration system from large volumes of potable water.Item A Study of Microfluidic Reconfiguration Mechanisms Enabled by Functionalized Dispersions of Colloidal Material for Radio Frequency Applications(2010-07-14) Goldberger, Sean A.Communication and reconnaissance systems are requiring increasing flexibility concerning functionality and efficiency for multiband and broadband frequency applications. Circuit-based reconfiguration mechanisms continue to promote radio frequency (RF) application flexibility; however, increasing limitations have resulted in hindering performance. Therefore, the implementation of a "wireless" reconfiguration mechanism provides the required agility and amicability for microwave circuits and antennas without local overhead. The wireless reconfiguration mechanism in this thesis integrates dynamic, fluidic-based material systems to achieve electromagnetic agility and reduce the need for "wired" reconfiguration technologies. The dynamic material system component has become known as electromagnetically functionalized colloidal dispersions (EFCDs). In a microfluidic reconfiguration system, they provide electromagnetic agility by altering the colloidal volume fraction of EFCDs - their name highlights the special considerations we give to material systems in applied electromagnetics towards lowering loss and reducing system complexity. Utilizing EFCDs at the RF device-level produced the first circuit-type integration of this reconfiguration system; this is identified as the coaxial stub microfluidic impedance transformer (COSMIX). The COSMIX is a small hollowed segment of transmission line with results showing a full reactive loop (capacitive to inductive tuning) around the Smith chart over a 1.2 GHz bandwidth. A second microfluidic application demonstrates a novel antenna reconfiguration mechanism for a 3 GHz microstrip patch antenna. Results showed a 300 MHz downward frequency shift by dielectric colloidal dispersions. Magnetic material produced a 40 MHz frequency shift. The final application demonstrates the dynamically altering microfluidic system for a 3 GHz 1x2 array of linearly polarized microstrip patch antennas. The parallel microfluidic capillaries were imbedded in polydimethylsiloxane (PDMS). Both E- and H-plane designs showed a 250 MHz frequency shift by dielectric colloidal dispersions. Results showed a strong correlation between decreasing electrical length of the elements and an increase of the volume fraction, causing frequency to decrease and mutual coupling to increase. Measured, modeled, and analytical results for impedance, voltage standing wave ratio (VSWR), and radiation behavior (where applicable) are provided.Item Applications of micro-3D printing to microfluidic cell dosing(2014-08) Robinson, Michael Mayes; Shear, Jason B.Cellular growth, development, differentiation, and death are mediated to some degree by the interaction of soluble factors with plasma membrane receptors. Traditionally the cellular response to chemical cues has been studied by exposing entire culture dishes to a desired reagent. While the addition of soluble reagents homogenously to cell culture dishes provides a basis for understanding much of cell biology, greater spatial resolution of reagent delivery is necessary in order to elucidate mechanisms on the subcellular scale. This dissertation explores techniques that may improve the quality and precision of delivering soluble factors to cultured cells in order to better understand the complex processes of cell biology. These advancements were made possible by applying high intensity, focused laser light to soluble materials to achieve microscopic three-dimensional (µ-3D) printing. In combination with a previously developed microfluidic cell dosing platform, microstructures were designed and µ-3D printed to hydrodynamically focus reagent streams for cell dosing. Structures were also µ-3D printed within micrometers of living cells from a solution of gelatin and bovine serum albumin with minimal cytotoxicity. When µ-3D printed, these proteins displayed both temperature and pH-responsive properties. In order to allow for on-the-fly control of reagent stream size and temporal pulse width, microstructures were µ-3D printed from temperature-responsive N- isoproplyacrylamide. To further improve the temporal resolution of the system, a technique for cycling between reagents with millisecond exchange times using laminar flow microfluidics was developed. The utility of these techniques was demonstrated by staining rat Schwann cells and mouse neuroblastoma rat glioma hybrid cells (NG108-15) with focused streams of fluorescent dyes. These advancements may allow future experiments to determine the placement of soluble factors necessary for bacterial quorum sensing or stem cell differentiation.Item Development of a Microfluidic Device for Synthesis of Lipid Bi-Layer In-Situ(2010-01-14) Banneyake, Bm U.Lipid bi-layers are ubiquitous components of biological cells and are found in a variety of cell components. In biological membranes, lipid bi-layer membranes carry membrane proteins, which control transport of material and communication of signals in and out the cell. There are several disadvantages involved with patch clamping method as a way of studying biological membranes and protein interactions. Hence, artificial synthesis of bi-layer has been of great interest in basic biophysical studies, drug discoveries in pharmaceutical studies and study of protein nanopores for precise engineering applications. However, conventional lipid bi-layer synthesis techniques require skilled operators, have low repeatability (reliability), have portability restrictions and result in unstable bi-layers having a short lifetime. In this investigation a novel microfluidic device and a method for artificial synthesis of lipid bi-layer in-situ are explored. In the proposed method, lipid trapped at an aperture on a Teflon sheet, is thinned to form a lipid bi-layer by a continuous flow of buffer solution on both sides of the aperture in the microfluidic device. The microfluidic device is expected to have advantages from its compact design. Further, the new approach is expected to be repetitive and good for automation removing the requirement of a skilled operator. The microfluidic device was fabricated using two glass substrates. Two channels of ? ? shape were etched and through holes were fabricated at all four terminal ends of the microchannels on each glass substrate. A thin Teflon sheet carrying a 100?m diameter hole was sandwiched between the two glass wafers forming two sets of microchannels on both sides of the aperture. An analytical microfluid model of the microchannels was developed to investigate the nature of the flow and to select microchannel parameters. Experiments using the proposed device were performed to verify the feasibility of the novel approach for lipid bi-layer synthesis. Experimental results suggest formation of a lipid bi-layer at an aperture on the Teflon sheet but further investigation might be necessary for verification. Life time of the bi-layer is short mainly due to low quality of the used aperture.Item Electrokinetic focusing of charged species at bipolar electrode in a microfluidic device(2010-12) Perdue, Robbyn K.; Crooks, Richard M.; Bard, Allen J.; Stevenson, Keith J.; Mullins, Charles B.; Stanton, John F.The development and characterization of bipolar electrode (BPE) focusing is described. BPE focusing is an electrokinetic equilibrium technique in which charged analytes are focused and locally enriched on an electric field gradient in the presence of a counter-flow. This electric field gradient is formed at the boundary of an ion depletion zone – the direct result of faradaic reactions occurring at the BPE in the presence of an externally applied electric field. Direct measurement of the electric field strength in the ion depletion region shows that the electric field is enhanced in this region and takes on a gradient shape, confirming the results of numerical simulations. Transient electric field measurements with simultaneous monitoring of a focused fluorescent tracer reveal that the field gradient forms rapidly upon application of the external field and remains stable over time with the tracer focused at a local field strength predicted by simple electrokinetic equations. These transient electric field measurements probe the effect of individual experimental parameters on the electric field gradient and the focused band. The results of these studies indicate that a steeper field gradient leads to enhanced concentration enrichment of the analyte. The slope of the gradient is increased with higher concentration of the running buffer and higher applied field strength. The addition of pressure driven flow across the microchannel moves the location of the field gradient and the position of the focused band. Further enhancement of enrichment is achieved through the suppression of Taylor dispersion after coating the microchannel with a non-ionic surfactant. The findings of these studies have motivated the transition of BPE focusing to smaller microchannels. A decrease in microchannel size not only decreases Taylor dispersion, but also provides access to higher buffer concentration and higher applied field strength, both of which enhance enrichment. The result is a three-order-of-magnitude increase in total analyte enrichment at a much higher enrichment rate. Furthermore, a dual channel configuration for BPE focusing is introduced which provides greater control over focusing conditions. Finally, the formation of ion depletion and enrichment zones at a BPE in a microchannel is shown to mimic ion concentration polarization (ICP) at micro-/nano-channel junctions. This is significant because this faradaic ICP provides a model to which traditional ICP can be compared and is achieved in a more easily fabricated device. In summary, the fundamental principles of BPE focusing are described. A greater understanding of the effect of experimental parameters on the focusing process leads to an unprecedented magnitude and rate of enrichment in a simple device architecture.Item Investigation of the photocatalytic lithographic deposition of metals in sealed microfluidic devices on TiO2 surfaces(2009-05-15) Castellana, Edward ThomasThe research presented within this dissertation explores the photocatalytic deposition of metal carried out within sealed microfluidic channels. Micro scale patterning of metals inside sealed microchannels is investigated as well as nanoscale control over the surface morphology of the nanoparticles making up the patterns. This is achieved by controlling solution conditions during deposition. Finally, the nanoparticle patterns are used in fabricating a sensor device, which demonstrates the ability to address multiple patches within a sealed channel with different surface chemistries. Also presented here is the construction of the first epifluorescence/total internal reflection macroscope. Its ability to carry out high numerical aperture imaging of large arrays of solid supported phospholipid bilayers is explored. For this, three experiments are carried out. First, imaging of a 63 element array where every other box contains a different bilayer is preformed, demonstrating the ability to address large scale arrays by hand. Next, a protein binding experiment is preformed using two different arrays of increasing ligand density on the same chip. Finally, a two-dimensional array of mixed fluorescent dyes contained within solid supported lipid bilayers is imaged illustrating the ability of the instrument to acquire fluorescent resonance energy transfer data. Additionally, the design and fabrication of an improved array chip and addressing method is presented. Using this new array chip and addressing method in conjunction with the epifluorescence/total internal reflection macroscope should provide an efficient platform for high throughput screening of important biological processes which occur at the surfaces of cell membranes.Item Measurement and control of complexity effects in branched microchannel flow systems(2012-05) Hart, Robert Andrew; Da Silva, Alexandre K., 1975-Complex flow structures consisting of branching, multi-scale, hierarchically arranged flow paths can be a beneficial in certain applications by providing lower hydraulic and thermal resistances than conventional flow arrangements. In this study, an experimental approach was used to investigate the hydrodynamic and thermal effects of the complexity, or degree of branching, in microscale complex flow structures. The primary focus of this work was to develop new concepts to advance the current capabilities of complex flow structures through management of complexity. The effects of complexity were determined from experiments performed on a set of microfluidic test sections which were identical except for the complexity of the underlying microchannel configuration. Comparison of the relative hydrodynamic and thermal performance indicates that complexity has a strong effect on both the pressure drop and heat transfer. When the pumping power is taken into account, the results suggest that higher complexity arrangements improve the overall thermal-hydraulic performance. This conclusion was confirmed by the trends observed in the coefficient of performance, a measure of the device thermal efficiency. To address the limitations of conventional fixed-complexity designs, the concept of a variable-complexity flow structure is developed. With a variable-complexity design, the configuration of a branched flow structure can be dynamically controlled to improve performance as operational conditions vary. This concept was successfully demonstrated by developing and testing an active variable-complexity microfluidic device in which pneumatically controlled microvalves were used to create different flow channel configurations. The variable-complexity concept was further refined by developing a microfluidic device with a passive variable-complexity design in which the flow channel configuration changed autonomously based on local temperatures. By using microvalves containing a temperature sensitive polymer, the flow configuration of the device was made thermally adaptive. Experiments were performed to characterize the behavior of the polymer microvalves and the overall device performance. The results showed that the device was capable of tracking changes in external heat sources by adapting and reconfiguring its internal flow structure. The experiments also showed how this variable-complexity design can reduce the pumping power expenditure by automatically directing flow only to areas where it is required.Item Study of microfluidic measurement techniques using novel optical imaging diagnostics(Texas A&M University, 2007-04-25) Park, JaesungNovel microscale velocity and temperature measurement techniques were studied based on confocal laser scanning microscopy (CLSM) and optical serial sectioning microscopy (OSSM). Two microscopic measurement systems were developed, 1) a CLSM micro particle image velocimetry (PIV) system with a dual Nipkow disk confocal unit (CSU-10), a CW argon-ion laser and an upright microscope, and 2) an OSSM micro- particle tracking velocimetry (PTV) system with an epi-fluorescence microscope and a non-designed specimen to make a three-dimensional (3-D) diffraction particle image. The CLSM micro-PIV system shows a unique optical slicing capability allowing true depth-wise resolved vector field mapping. A comparative study is presented between the CLSM micro-PIV and a conventional epi-fluorescence micro-PIV. Both have been applied to the creeping Poiseuille flows in two different microtubes of 99-????m (Re = 0.00275) and 516-????m ID diameters (Re = 0.021). The CLSM micro-PIV consistently shows significantly improved particle image contrasts, the definition of "optical slicing" and measured flow vector fields more accurately agreeing with predictions based on the Poiseuille flow fields, compared to the conventional micro-PIV. The OSSM micro-PTV technique is applied for a 3-D vector field mapping in a microscopic flow and a Brownian motion tracking of nanoparticles. This technique modifies OSSM system for a micro-fluidic experiment, and the imaging system captures a diffracted particle image having numerous circular fringes instead of an in-focus particle image. The 3-D particle tracking is based on a correlation between the 3-D diffraction pattern of a particle and the defocus distance from a focal plane. A computational program is invented for the OSSM micro-PTV, and provides a 3-D velocity vector field with a spatial resolution of 5.16 ????m. In addition, a concept of nonintrusive thermometry is presented based on the correlation of the Brownian motion of suspended nanoparticles with the surrounding fluid temperature. Detection of fully three-dimensional Brownian motion is possible by the use of the OSSM, and the measured value of mean square displacement (MSD) is compared fairly well with Einstein's predictions.