Theses and Dissertations at Montana State University (MSU)
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Item Electrochmical impedance spectroscopy biosensor platform for evaluation of biofilm(Montana State University - Bozeman, College of Engineering, 2023) McGlennen, Matthew Connor Dusenbery; Co-chairs, Graduate Committee: Christine Foreman and Stephan Warnat; This is a manuscript style paper that includes co-authored chapters.Microbial biofilms are organized communities of surface-attached microorganisms encased in a self-produced extracellular matrix that pose significant challenges in medicine, the environment, and industry. Biofilms can cause chronic infections, biofouling, and equipment failure, while existing methods for biofilm detection are slow, costly, and labor-intensive. Recently, the use of microfabricated electrochemical impedance spectroscopy (EIS) biosensors has emerged as a promising technique for evaluating biofilm growth in real-time with advantages of small-size, adaptability, low-cost, and high-sensitivity. In this work, EIS biosensors featuring gold micro-interdigitated electrodes were produced using standard microfabrication techniques. Sensors were integrated into a custom 3D-printable flow cell system, enabling EIS measurements and confocal laser scanning microscopy (CLSM) imaging simultaneously. Green fluorescently labeled Pseudomonas aeruginosa PA01, a model biofilm forming bacteria, was introduced into flow chambers and subsequent growth was monitored by EIS, CLSM, and biomass enumeration. Using the system, biofilm growth, dispersal, and the effects of cell-signaling suppression were evaluated. The sensors were also tested in an oil-water emulsion and field-tested on an alpine snow-patch and pond. Improved stability of EIS measurements was achieved by coating the sensors' counter and reference electrodes with an electrically conductive polymer. Biofilm growth was successfully detected using EIS biosensors at an optimized single-frequency, with average decreases in impedance of ~22% by 24 hours. Likewise, biofilm dispersal via chemical treatments were successfully detected with average increases in impedance of ~14% over the ensuing 12 hours. When cells were exposed to a quorum sensing inhibition agent, impedance did not decrease for 18 hours. Impedance changes due to biofilm growth, dispersal, and effects of quorum sensing inhibition were validated by CLSM images and biofilm enumeration. Similarly, in an oil-water emulsion the biosensors successfully detected biofilm growth, dispersal, and effects of quorum sensing inhibition. In an alpine field-test, samples containing varying concentrations of microbes could be detected using the EIS biosensors. This work demonstrates that EIS biosensors are a promising tool for real-time monitoring of biofilm dynamics in a variety of aqueous environments. Overall, EIS biosensing holds great potential for in situ and real-time data regarding biofilm colonization that is not possible with existing techniques.Item Fabrication of subwavelength scale optical nanostructures(Montana State University - Bozeman, College of Engineering, 2011) Haq, Mohammad Tahdiul; Chairperson, Graduate Committee: Wataru NakagawaSub-wavelength scale optical nanostructures can be engineered for specific applications in multiple disciplines. This thesis describes the fabrication of three such optical nanostructures and the process development and optimization performed to improve the nanofabrication capabilities of our research group. Along with our collaborators we have fabricated a subwavelength-scale solid immersion lens. The fabrication process of cylinders of precise dimensions in resist is discussed as well as the measurements and characterization of the final fabricated device. The second device is a1-D antireflective rectangular grating in silicon with 800nm period, which is fabricated, simulated and characterized. The lithography process is calibrated for gratings with 250-600nm line widths and the etching process is optimized to obtain depths precise to within + or - 10nm. The final device is a mid-infrared polarizing beam splitter. The fabrication of this device is not yet complete, but the correct grating structure in silicon is fabricated and some process improvements for gold deposition have been realized.