Date of Award
Master of Science
AN ABSTRACT OF THE THESIS OF ZACHARIA THARAKAN, for the Master of Science degree in BIOMEDICAL ENGINEERING, presented on 11/06/17, at Southern Illinois University Carbondale. TITLE: FABRICATION AND CHARACTERIZATION OF PIEZOELECTRIC ZINC OXIDE NANOWIRE SENSOR MAJOR PROFESSOR: Dr. Farhan Chowdhury The biosensor field is rapidly accelerating in recent years. Among many types of biosensors available today, piezoelectric (PZT) class of materials are becoming very popular. In this thesis, Zinc Oxide nanowire PZT biosensor was fabricated and characterized to detect the presence of fungi which has some huge economic implications in US agriculture industry. Zinc Oxide nanowires were synthesized in a mass scale via wet solution method in a controlled temperature and growth environment. Different substrates including glass, indium tin oxide, and gold coated silicon substrates were utilized to grow the nanowires followed by layering with silane and subsequently etching them. The results show that the nanowires were grown homogenously on gold coated silicon wafers with cylindrical structures. The ideal morphology of the nanowires was found to be dependent on: incubation time, incubation temperature, and substrate material. Substrate catalyst was also varied from Au & Pd to pure Au which showed significant improvement in producing the nanowires. A systematic variation of hours was implemented from: 3, 5, 7, 9, 11, and 13 hours. Zinc Oxide nanowire features such as length, diameter, and aspect ratio were quantified through SEM micrographs. Linear increase in height, diameter, and aspect ratio was observed up to 13 hours along with density. The optimal condition for nanowire growth was determined at: 80 °C and 5 hours. Energy dispersive spectroscopy aided in generating presence of specific elements on the biosensor. Raman helps in verifying chemical composition of the device. Both Raman and EDS spectroscopy aided in enhancement and individualization of the biosensor at different proposed parameters. Keithley readings represented series of current-voltage (I-V) measurements under different forward biased voltages. The response of nanowires from these I-V measurements show a diode-like response. Next, nanowire displacement patterns of fungi, Fusarium proliferatum (F. proliferatum) were studied by I-V measurements. When I-V measurements were conducted on PZT nanowires in the presence of F. proliferatum a strong association from microbe attachment and growth was observed showing an increase in switch-on voltage with a 2V sweep. It is speculated that the observed high resistance is a result of mechanical movement of fungi on the piezoelectric device. Future studies will be designed to investigate this phenomenon. These results indicate that by simply reading the characteristic current-voltage measurement, one can better evaluate microbe pattern of displacement and maturation. Future application of this nanowire platform can characterize distinct displacement signature of disease carrying organism much more efficiently.
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