Browsing by Subject "microfluidics"
Now showing 1 - 14 of 14
Results Per Page
Sort Options
Item Characterization and applications of microfluidic devices based on immobilized biomaterials(Texas A&M University, 2007-04-25) Heo, JinseokMicrofluidic biosensors and bioreactors based on immobilized biomaterials are described in this dissertation. Photocrosslinkable hydrogel or polymeric microbeads were used as a supporting matrix for immobilizing E.coli or enzymes in a microfluidic device. This dissertation covers a microfluidic bioreactor based on hydrogel-entrapped E.coli, a microfluidic biosensor based on an array of hydrogel-entrapped enzymes, and a microfluidic bioreactor based on microbead-immobilized enzymes. Hydrogel micropatches containing E.coli were fabricated within a microfluidic channel by in-situ photopolymerization. The cells were viable in the hydrogel micropatch and their membranes could be porated by lysating agents. Entrapment of viable cells within hydrogels, followed by lysis, could provide a convenient means for preparing biocatalysts without the need for enzyme extraction and purification. Our results suggested that hydrogel-entrapped cells, immobilized within microfluidic channels, can act as sensors for small molecules and as bioreactors for carrying out reactions. A microfluidic biosensor based on an array of hydrogel-entrapped enzymes could be used to simultaneously detect different concentrations of the same analyte or multiple analyte in real time. The concentration of an enzyme inhibitor could be quantified using the same basic approach. Isolations of the microchannels within different microfluidic channels could eliminate the possibility of cross talk between enzymes. Finally, we characterized microfluidic bioreactors packed with microbead-immobilized enzymes that can carry out sequential, two-step enzyme-catalyzed reactions under flow conditions. The overall efficiency of the reactors depended on the spatial relationship of the two enzymes immobilized on the beads. Digital simulations confirmed the experimental results.Item Collection, focusing, and metering of DNA in microchannels using addressable electrode arrays for portable low-power bioanalysis(Texas A&M University, 2008-10-10) Shaikh, FaisalAlthough advances in microfluidic technology have enabled increasingly sophisticated biosensing and bioassay operations to be performed at the microscale, many of these applications employ such small amounts of charged biomolecules (DNA, proteins, peptides) that they must first be pre-concentrated to a detectable level. Efficient strategies for precisely handling minute quantities of biomolecules in microchannel geometries are critically needed, however it has proven challenging to achieve simultaneous concentration, focusing, and metering capabilities with currentgeneration sample injection technology. Using microfluidic chips incorporating arrays of individually addressable microfabricated electrodes, we demonstrate that DNA can be sequentially concentrated, focused into a narrow zone, metered, and injected into an analysis channel. The technique used in this research transports charged biomolecules between active electrodes upon application of a small potential difference (1 V), and is capable of achieving orders of magnitude concentration increases within a small device footprint. The collected samples are highly focused, with sample zone size and shape defined solely by electrode geometry. In addition to achieving the objectives of the research project, this setup was found to provide added functionality as a label-free biomolecule detection technique due to the formation of light scattering phases of charged biomolecules on top of the capture electrode.Item Electrokinetic concentration enrichment within a microfluidic device integrated with a hydrogel microplug(2009-05-15) Dhopeshwarkar, Rahul RajeshA simple and efficient technique for the concentration enrichment of charged species within a microfluidic device was developed. The functional component of the system is a hydrogel microplug photopolymerized inside the microfluidic channel. The fundamental properties of the nanoporous hydrogel microplug in modulating the electrokinetic transport during the concentration enrichment were investigated. The physicochemical properties of the hydrogel plug play a key role in determining the mode of concentration enrichment. A neutral hydrogel plug acts as a physical barrier to the electrophoretic transport of charged analytes resulting in size-based concentration enrichment. In contrast, an anionic hydrogel plug introduces concentration polarization effects, facilitating a size and charge-based concentration enrichment. The concentration polarization effects result in redistribution of the local electric field and subsequent lowering of the extent of concentration enrichment. In addition, an electroosmotic flow originating inside the pores of the anionic hydrogel manipulates the location of concentration enrichment. A theoretical model qualitatively consistent with the experimental observations is provided.Item Fabrication of masters for microfluidic devices using conventional printed circuit technology(Texas A&M University, 2004-09-30) Sudarsan, Arjun PenuboluThe capability to easily and inexpensively fabricate microfluidic devices with negligible dependence on specialized laboratory equipment continues to be one of the primary forces driving the widespread use of plastic-based devices. These devices are typically produced as replicas of a rigid mold or master incorporating a negative image of the desired structures. The negative image is typically constructed from either thick photoresists or etched silicon substrates using conventional photolithographic fabrication processes. While these micromachining techniques are effective in constructing masters with micron-sized features, the need to produce masters rapidly in order to design, fabricate, and test microfluidic devices, is a major challenge in microfluidic technology. In this research, we use inexpensive photosensitized copper clad circuit board substrates to produce master molds using conventional printed circuit technology. The techniques provide the benefits of parallel fabrication associated with photolithography without the need for cleanroom facilities, thereby offering a degree of speed and simplicity that allows microfluidic master molds to be constructed in approximately 30 minutes in any laboratory. These techniques are used to produce a variety of microfluidic channel networks using PDMS (polydimethylsiloxane) and melt-processable plastic materials.Item Flow-Through Microfluidic Device for High-Efficiency Transfection of Mammalian Cells through Combined Microelectroporation and Sonoporation(2012-07-16) Longsine, Whitney LeighIn this study we are presenting a proof-of-concept microfluidic device that simultaneously applies the conditions required for microelectroporation and micro-sonoporation in a flow-through fashion that allows for high throughput, high efficiency transfection of mammalian cells. During the design stage, we developed a low-cost, high-resolution polymer microfabrication technique termed laser stenciling. While few other electro-sonoporation protocols have been reported, to the best of our knowledge, we are the first to incorporate microelectroporation, which has been well established in literature to be advantageous to conventional electroporation, with flow-through micro-sonoporation. When comparing transfection efficiency for our electro-sonoporation method to that of sonoporation or microelectroporation alone, we observed single batch improvements up to 20 percent and 17 percent, respectively. The average improvement in efficiency was approximately 15 percent greater than achieved with sonoporation and 10 percent greater than that of electroporation. Importantly, there was little difference in short term cell viability between the three methods (maintained at > 90 percent). The average transfection efficiency for electro-sonoporation was 81.25 percent and cell viability was 91.56 percent. Overall, we have presented a device and electro-sonoporation method that meets or outperforms the transfection efficiency and cell viability standards for HeLa cells set by other reported electroporation and sonoporation methods.Item Kinetics of an Inverse Temperature Transition Process and Its Application on Supported Lipid Bilayer(2011-10-21) Chang, Chin-YuanThis dissertation focuses on the study of inverse temperature transition processes of the poly(N-isopropylacrylamide) (PNIPAM) and the elastin-like polypeptides (ELPs). A novel temperature jump microfluidic system is introduced and this system shows the ability to measure the kinetics of the PNIPAM and the ELPs collapse without a heat transfer problem. The conformational change of the ELPs during the phase transition process is utilized as a nanoscale protein filter to modulate ligandreceptor binding events on supported lipid bilayers (SLBs). This research study is divided into three main parts. The first part is the development of the temperature jump microfluidics. The kinetics of PNIPAM collapse is used as a model system to show the capability of this new device to measure millisecond time scale phase transition processes. The effects of salts on the kinetics of PNIPAM collapse are also shown in this part. To our knowledge, this is the first study which shows the effects of salts on PNIPAM collapse kinetics. The second part of this research is the application of the novel temperature jump microfluidics. The hydrophobic collapse of ELPs composed of identical sequence but different chain length is investigated. By controlling the molecular weight of the ELPs, the thermodynamic contributions from intermolecular hydrophobic interactions, and intramolecular hydrophobic interactions could be calculated individually for this unique system. The third part is the application of the phase transition property of ELPs. The ELPs are conjugated on the surface of the SLBs as a nanoscale protein filter. The conformation of the ELPs can be modulated by ionic strength of the buffer solution or ambient temperature. The ELPs conjugated SLBs platform showed the ability to block IgG binding to biotin conjugated on the SLBs when the ELPs were in the extended coil state and open the access for protein to bind to biotin in compact globule conformation.Item Layer-by-Layer Assembled Smectite-Polymer Nanocomposite Film for Rapid Detection of Low-Concentration Aflatoxins(2012-11-01) Hu, He 1987-Aflatoxin is a potent biological toxin produced by fungi Aspergillus flavus and A. parasiticus. Current quantification methods for aflatoxins are mostly established on immunoaffinity columns which are both costly and labor intensive. Inspired by smectites? high aflatoxin adsorption capacity and affinity, a novel aflatoxin quantification sensor based on smectite-polyacrylamide (PAM) nanocomposite was fabricated. First, a smectite-PAM nanocomposite film was synthesized on flat silicon substrates which assembled smectite particles from the clay suspension. A layer-by-layer assembly process was developed to achieve uniform morphology and thickness of the nanocomposite films. During the aflatoxin quantification process, positive correlations between the fluorescence intensity from the aflatoxin B1 (AFB1) adsorbed smectite-PAM nanocomposite films and the AFB1 concentration in the test solutions were obtained. The smectite-PAM nanocomposite film has shown similar AFB1 adsorption capabilities as the smectite. Second, the smectite-PAM nanocomposite film was optimized in order to achieve the aflatoxin quantification at ppb level (below 20ppb) in corn extraction solutions. The smectite was modified by Ba2+, which had demonstrated to be able to improve its aflatoxin adsorption capacity. PAM aqueous solutions with the mass concentration ranging from 0.8% to 0.001% were tested. The results showed that the nanocomposite synthesized from 0.005% concentration of PAM solution generated the best properties. After the optimization, the smectite-PAM nanocomposite films achieved the detection of aflatoxin B1, B2, G1 and G2 (AFB2, AFG1 and AFG2) in 10 ppb corn extraction solution. Aflatoxin quantifications in AFB1 and AFB2 mixture solution, AFB1 and AFB2 mixture solution and AFB1 and AFG1 mixture solution were conducted, and the recoveries of last test ranged from 90.52% to 110.11% at low aflatoxin concentration (below 20 ppb). Third, in order to shorten the quantification duration and simplify the detection process, a novel aflatoxin detection array based on smectite-PAM nanocomposite and an improved fluorometric quantification method were developed. Through a microfluidic chip, the reaction time was reduced to 10~20min. Two concentration levels (20~80ppb/5~15ppb) of aflatoxin B1 spiked corn extraction solutions were tested. In the fluorometric quantification step, a common lab-use 365 nm ultraviolet lamp replaced the spectrofluorometer which simplified and accelerated the process.Item Micro-chamber filling experiments for validation of macro models with applications in capillary driven microfluidics(2009-05-15) Gauntt, Stephen ByronPrediction of bubble formation during filling of microchambers is often critical for determining the efficacy of microfluidic devices in various applications. In this study experimental validation is performed to verify the predictions from a previously developed numerical model using lumped analyses for simulating bubble formation during the filling of microchambers. The lumped model is used to predict bubble formation in a micro-chamber as a function of the chamber geometry, fluid properties (i.e. viscosity and surface tension), surface condition (contact angle, surface roughness) and operational parameters (e.g., flow rate) as user defined inputs. Several microchambers with different geometries and surface properties were microfabricated. Experiments were performed to fill the microchambers with different liquids (e.g., water and alcohol) at various flow rates to study the conditions for bubble formation inside the microchambers. The experimental data are compared with numerical predictions to identify the limitations of the numerical model. Also, the comparison of the experimental data with the numerical results provides additional insight into the physics of the micro/nano-scale flow phenomena. The results indicate that contact angle plays a significant role on properties of fluids confined within small geometries, such as in microfluidic devices.Item Microfluidic Investigation of Tracer Dye Diffusion in Alumina Nanofluids(2012-10-05) Ozturk, Serdar 1979-Nanofluids, a new class of fluids engineered by suspending nanometer-sized particles in a host liquid, are offered as a new strategy in order to improve heat and mass transfer efficiency. My research was motivated by previous exciting studies on enhanced mass diffusion and the possibility of tailoring mass transport by direct manipulation of molecular diffusion. Therefore, a microfluidic approach capable of directly probing tracer diffusion between nanoparticle-laden fluid streams was developed. Under conditions matching previously reported studies, strong complexation interactions between the dye and nanoparticles at the interface between fluid streams was observed. When the tracer dye and surfactant were carefully chosen to minimize the collective effects of the interactions, no significant change in tracer dye diffusivity was observed in the presence of nanoparticles. Next, adapting tracer dyes for studies involving colloidal nanomaterials was explored. Addition of these charged tracers poses a myriad of challenges because of their propensity to disrupt the delicate balance among physicochemical interactions governing suspension stability. Here it was shown how important it is to select the compatible combinations of dye, nanoparticle, and stabilizing surfactant to overcome these limitations in low volume fraction (< 1 vol%) aqueous suspensions of Al2O3 nanoparticles. A microfluidic system was applied as a stability probe that unexpectedly revealed how rapid aggregation could be readily triggered in the presence of local chemical gradients. Suspension stability was also assessed in conjunction with coordinated measurements of zeta potential, steady shear viscosity and bulk thermal conductivity. These studies also guided our efforts to prepare new refrigerant formulations containing dispersed nanomaterials, including graphene nanosheets, carbon nanotubes and metal oxide and nitride. The influence of key parameters such as particle type, size and volume fraction on the suspension's thermal conductivity was investigated using a standard protocol. Our findings showed that thermal conductivity values of carbon nanotube and graphene nanosheet suspensions were higher than TiO2 nanoparticles, despite some nanoparticles with large particle sizes provided noticeable thermal conductivity enhancements. Significantly, the graphene containing suspensions uniquely matched the thermal conductivity enhancements attained in nanotube suspensions without accompanying viscosity, thus making them an attractive new coolant for demanding applications such as electronics and reactor cooling.Item Microfluidically Cryo-Cooled Planar Coils for Magnetic Resonance Imaging(2013-08-09) Koo, ChiwanHigh signal-to-noise ratio (SNR) is typically required for higher resolution and faster speed in magnetic resonance imaging (MRI). Planar microcoils as receiver probes in MRI systems offer the potential to be configured into array elements for fast imaging as well as to enable the imaging of extremely small objects. Microcoils, however, are thermal noise dominant and suffer limited SNR. Cryo-cooling for the microcoils can reduce the thermal noise, however conventional cryostats are not optimum for the microcoils because they typically use a thick vacuum gap to keep samples to be imaged to near room temperature during cryo-cooling. This vacuum gap is typically larger than the most sensitive region of the microcoils that defines the imaging depth, which is approximately the same as the diameters of the microcoils. Here microfluidic technology is utilized to locally cryo-cool the microcoils and minimize the thermal isolation gap so that the imaging surface is within the imaging depth of the microcoils. The first system consists of a planar microcoil with microfluidically cryo-cooling channels, a thin N2 gap and an imaging. The microcoil was locally cryo-cooled while maintaining the sample above 8?C. MR images using a 4.7 Tesla MRI system shows an average SNR enhancement of 1.47 fold. Second, the system has been further developed into a cryo-cooled microcoil system with inductive coupling to cryo-cool both the microcoil and the on-chip microfabricated resonating capacitor to further improve the Q improvement. Here inductive coupling was used to eliminate the physical connection between the microcoil and the tuning network so that a single cryocooling microfluidic channel could enclose both the microcoil and the capacitor with minimum loss in cooling capacity. Q improvement was 2.6 fold compared to a conventional microcoil with high-Q varactors and transmission line connection. Microfluidically tunable capacitors with the 653% tunability and Q of 1.3 fold higher compared to a conventional varactor have been developed and demonstrated as matching/tuning networks as a proof of concept. These developed microfluidically cryo-cooling system and tunable capacitors for improving SNR will potentially allow MR microcoils to have high-resolution images over small samples.Item Monodispersed polygonal water droplets in microchannel(2009-05-15) Mehrotra, RajatThe fabrication, motion and behavior of small droplets are subjects under considerable current study. The possible applications include using droplets as actuators to enhance mixing, as chemical reactors and the formation of emulsions. Microfluidics provides a convenient means of producing droplets at the micro scale. The study is currently dominated by spherical systems where droplets are consistently spherical in nature. Various methods and geometries have been tested for fabricating these droplets but little research has been conducted towards producing non-circular droplets. While the fabrication of non-spherical droplets has been reported before control over their shape remains difficult to achieve. In this thesis, we present a method to fabricate droplets using shear focusing in an oil medium alternatively from two channels facing each other. The droplets produced are non-circular in shape, and their shape dynamically alters as they travel in the microfluidic channel. The size of the droplets can be controlled by the ratio of oil and water flow rates. Microscopic images have been presented that show the non-spherical shape of the droplets at the point of fabrication. Images taken at two points further along the microfluidic channel show how the shapes of these droplets change as they travel in the channel. There were three regimes of droplet shapes, circular, triangular and rectangular shapes that were determined by the packing ratio of water droplet in oil phase in microfluidic channels. All droplets formed in this experiment were monodispersed.Item Multivortex micromixing: novel techniques using Dean flows for passive microfluidic mixing(Texas A&M University, 2007-04-25) Sudarsan, Arjun PenuboluMixing of fluids at the microscale poses a variety of challenges, many of which arise from the fact that molecular diffusion is the dominant transport mechanism in the laminar flow regime. The unfavorable combination of low Reynolds numbers and high P????clet numbers implies that cumbersomely long microchannels are required to achieve efficient levels of micromixing. Although considerable progress has been made toward overcoming these limitations (e.g., exploiting chaotic effects), many techniques employ intricate 3-D flow networks whose complexity can make them difficult to build and operate. In this research, we show that enhanced micromixing can be achieved using topologically simple and easily fabricated planar 2-D microchannels by simply introducing curvature and changes in width in a prescribed manner. This is accomplished by harnessing a synergistic combination of (i) Dean vortices that arise in the vertical plane of curved channels as a consequence of an interplay between inertial, centrifugal, and viscous effects, and (ii) expansion vortices that arise in the horizontal plane due to an abrupt increase in a conduit??????s cross-sectional area. We characterize these effects using top-view imaging of aqueous streams labeled with tracer dyes and confocal microscopy of aqueous fluorescent dye streams, and by observing binding interactions between an intercalating dye and double-stranded DNA. These mixing approaches are versatile, scalable, and can be straightforwardly integrated as generic components in a variety of lab-on-a-chip systems.Item Novel design of a passive microfluidic mixer for biochemical reactions and biosensing(2009-05-15) Yee, Yao-ChungThe next step in miniaturization of analytical devices involves the use of MEMS and Lab-on-a-Chip applications, where many biological or chemical reactions are carried out on the device in real time. Since detection mechanisms occur almost immediately after the reactions, inefficient mixing of reagents could cause a decrease in sensing capability, especially on micro- and nano-scaled devices. Thus a microfluidic mixer has become a crucial component in these applications. Here we propose a new design of a passive microfluidic mixer that utilizes the theories of chaotic advection to enhance mixing. The micro-channels for the mixer have dimensions with width ranging from 10?m to 40?m, depth 40?m, and a total length of 280?m. First the designs are simulated using CFD-ACE+ for computational analysis. After the device geometry has been decided, the actual devices are fabricated using traditional UV photolithography on silicon and bonded with pyrex glass by anodic bonding. To test the actual device mixing efficiency, we used a fluorescent dye rhodamine B solution to mix with DI water and put the devices under fluorescent microscope observations for real-time analysis. Images of fluorescent light intensities are taken at different flow rates during the analysis and are later used to study the experimental results calculated using a published mixing efficiency formula for comparison.Item Studies in biological surface science: microfluidics, photopatterning and artificial bilayers(Texas A&M University, 2004-09-30) Holden, Matthew AlexanderHerein is presented the collective experimental record of research performed in the Laboratory for Biological Surface Science. These investigations are generally classified under the category of bioanalytical surface science and include the following projects. Chapters III and IV describe the creation of a microfluidic device capable of generating fixed arrays of concentration gradients. Experimental results were matched with computational fluid dynamics simulations to predict analyte distributions in these systems. Chapters V and VI demonstrate the discovery and utility of photobleaching fluorophores for micropatterning applications. Bleached fluorophores were found to rapidly attach to electron rich surfaces and this property was used to pattern enzymes inside microfluidic channels in situ. Finally, Chapter VII exhibits a method by which solid supported lipid bilayers can be dried and preserved by specifically bound proteins. The intrinsic property of lateral lipid mobility was maintained during this process and a mechanism by which the protein protects the bilayer was suggested.