Browsing by Subject "Microfluidic"

Now showing 1 - 3 of 3
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    Fabrication and characterization of a polydimethylsiloxane microfluidic pump for direct-sampling neuroscience experiments, with in-line capillary electrophoresis - laser-induced fluorescence chemical analysis
    (2011-05) Graf, Neil J.
    A polydimethylsiloxane (PDMS) peristaltic micropump was designed, fabricated, and characterized, for intended use within rodent brain direct-sampling neuroscience experiments, with capillary electrophoresis - laser-induced fluorescence (CE-LIF) chemical analysis. The micropump was fabricated in-part using replica molding (REM) and injection molding. The micropump channel was formed by bonding an open PDMS Gaussianshaped micromolded channel, to a featureless slab of PDMS. Two pieces of capillary tube interconnects were sealed within the closed-off microchannel, and used to make connections with the outside world. The micropump was actuated using piezoelectric cantilevers, with a precision machined microvalve attached to the tip of each cantilever actuator. Registration of the cantilevers and microvalves over the PDMS microchannel, was accomplished with the aid of in-house machined micropositioners. The micropump was thoroughly characterized, for use and application as a bio-analytical add-on attachment device, to an already existing CE-LIF instrument. The micropump was characterized for: various microchannel geometries; different microvalve sizes, tilt, positioning, and shutoff performance; micropositioner design and performance; and, flow rate, backpressure, and peristaltic signal analysis. A P-Q (or H-Q) plot was formed, to represent the performance of the micropump for maximum attainable backpressure (P), versus flow rate (Q). The linear plot was formed by experimentally collecting fourteen individual data points, each corresponding to a unique micropump, “state.” The P-Q plot as discussed within Chapter VIII, is very potent, in providing a 5-for-1 benefit ratio. The P-Q plot allows an experimentalist to obtain: 1) a means to understand how the micropump output performance for both flow rate and backpressure, can be optimized for any particular microfluidic application, 2) an experimentally characterized micropump performance curve/s, 3) an experimentally characterized system curve, 4) the maximum power output of the micropump, and 5) a means to acquire a quantitative measure of the suction lift requirements associated with rodent brain direct-sampling neuroscience experiments. A control volume analysis is provided, to additionally articulate and facilitate discussion of the direct-sampling methodology. Preliminary pilot study direct-sampling data is also provided, as a means to justify and prove viability of the direct-sampling technique, for future characterization and optimization direct-sampling CE-LIF neuroscience studies.
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    Fabrication of a PDMS microfluidic device for size selective DNA transport and single-stranded DNA generation for SELEX
    (2012-07) Sheng, Yixiao
    An innovative nanopore based microfluidic device for SELEX has been developed for single-stranded DNA generation and sizing. The objective of my research is to design, fabricate, test and model this device and make this device applicable for SELEX. The nanopores of the membrane controls fluidic transport between different planes in the device. It adds more functionality and flexibility to the microfluidic device. This device consists of two polydimethylsiloxane (PDMS) channels separated by a polycarbonate membrane. Channels were designed in a CAD software and a master was fabricated using rapid prototyping of PDMS. Multiple PDMS replicas were then cast from this master. The membrane was sandwiched between two channels. Oxygen plasma treatment was applied to bond two PDMS layers and glass substrates were used to support the whole device. Recovery of fluorescein across the membrane was compared with 10 and 80 nucleotide (nt) single stranded DNA(ssDNA) to characterize the device. Recovery of analytes improved with decreasing flow rate. Size selectivity was observed. Two mathematical models which were built based on conservation of mass and constitutive relationships described the process of DNA transportation in the microfluidic device. Trends in recovery measured at various flow rates were consistent with the trends predicted in the two models which support the premise that diffusion dominated the molecular transport in this device. In addition to that, Model 2 demonstrated recovery was affected by the ionic strength of the buffer as well. One application of this device was to automate the process to make double stranded DNA(dsDNA) single stranded which can be integrated into an automatic SELEX system. Streptavidin-coated polystyrene beads were immobilized with dual-biotin labeled dsDNA and alkaline treatment was adopted to denature dsDNA and release the non-biotinylated ssDNA. 25mM sodium hydroxide (NaOH) was optimized to achieve the best purity. 95.7% of the strands collected across the membrane were the non-biotinylated ssDNA. Capillary Electrophoresis (CE) results confirmed that the non-biotinylated ssDNA was the major component across the membrane.
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    Pathogen Quantification and Risk Assessment of Water Reuse Systems in the State of Minnesota
    (2019-12) Dooling, Valerie
    There is a growing interest in reusing or reclaiming water for non-potable use; however, one of the largest barriers to implementation is unknown source water quality and what risks are present. This work was conducted to determine the number of pathogens and their concentration present in currently operational water reuse systems in Minnesota, and to collect design treatment information from each reuse site and compare to pathogen and indicator quantity. Eighty-three samples were collected from 25 sites and were simultaneously analyzed for 27 bacterial and viral genes through microfluidic qPCR. Findings are that indicators and chemical tests did not correlate with type of source water. Type of treatment does not consistently correlate to log10 reduction, and only wastewater disinfection consistently removed all pathogens from treatment. Ten different pathogens were detected in water reuse systems. Quantitative Microbial Risk Assessment was performed on six pathogens in four exposure scenarios. Findings are that annual risk of infection of non-treated water is greater than recreational water benchmarks, however, the extent of risks depend on the exposure. When only considering samples from distribution or post-treatment sites, the risks are considerably lower, and often within guidelines.