Browsing by Author "Dr. Albert Banes, Committee Member"

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    Characterization and Evaluation of a Novel Nanoporous Gold Biosensor Substrate.
    (2009-07-22) Pierson, Bonnie Elizabeth; Dr. Albert Banes, Committee Member; Dr. Roger Narayan, Committee Chair; Dr. Nancy Monteiro-Riviere, Committee Member
    Dilute but powerful biological markers, such as hormones in blood stream, are potent but difficult to detect quickly and accurately using current biosensor technologies. Nanoporous structures offer greatly increased surface area which can be functionalized for use as a biosensor, amplifying throughput and the enhancing the ability to detect small concentrations. With the option for diverse component materials and conformations, a sensor with prescribed properties could be easily incorporated into devices for clinical diagnosis or research applications. This study evaluates the suitability of a nanoporous gold (NPG) wire for use as a biosensing component as a proof of concept through the detailed characterization of the porosity, structural support, and electrical properties of the wires. The nanoporous gold wires were created using electrochemical etching equipment. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were used to image and evaluate the pores and effectiveness of the etching procedure. Pores were found to be 9.86 ± 4.92 µm in diameter with a density of 880 pores/µm2 and only 5% silver remained following etching procedures. The storage capacity of the nanoporous wire annealed to a gold support structure at 15.6 mF/cm, was found to be higher than that of unsupported wires at 10.6 mF/cm. Structurally supported NPG wires also demonstrated a lower resistance (4.2Ω compared to 13.4Ω) owing to the capacitance of the nonporous gold support structure at high frequencies. Wires annealed to a gold support structure demonstrated greater mechanical stability and generally more consistent electrical properties. Samples were found highly susceptible to fracture and any coatings vulnerable to denaturing with extensive transport, handling, and testing. Some cross-contamination of samples was detected. Most contamination effects were minimal and confined to materials used in the manufacturing process. Future investigation should include other support structure conformations, functionalizing samples, and performing biocompatibility testing. NPG wires demonstrate potential for environmental applications and as medical device component, but have not yet been evaluated for direct-contact in vivo applications. The brittleness of the material necessitates that it be used in conjunction with other support structures; however the material provides interesting electrical properties, a good base for the adhesion of biomolecules, and a thorough porosity.
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    Microstructural, Mechanical and Antibacterial Characterization of Nanocrystalline Diamond Thin Films
    (2007-04-08) Lewis, Jamal Sana; Dr. Peter Mente, Committee Member; Dr. Albert Banes, Committee Member; Dr. Roger Narayan, Committee Chair
    Nanocrystalline diamond thin films exhibit unusual hardness, wear resistance, and corrosion resistance properties, and are currently being considered for use in orthopaedic, ophthalmic, and other medical implants. The purpose of this study was to evaluate the hardness, Young's modulus, microscratch adhesion, and antimicrobial properties of nanocrystalline diamond thin films. Microwave plasma enhanced chemical vapor deposition (MPCVD) was used to deposit nanocrystalline diamond thin films on p-type silicon wafers. Raman spectroscopy, scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HRTEM) were used to determine quality and phase purity of the nanocrystalline diamond thin films. The thin films consisted of diamond nodules that varied in morphology (size=60-600 nm). HRTEM showed that the films contained rectangular crystallites with dimensions between 2 — 4 nm. Raman spectroscopy confirmed that the thin film sample contained both tetrahedrally-bonded and amorphous carbon phases. The hardness and Young's modulus values for the nanocrystalline diamond thin films were 29.4 ± 11.9 GPa to 72.0 ± 10.7 GPa and 346.4 ± 98 GPa to 551.8 ± 71.5 GPa, respectively. Microscratch adhesion testing was performed on the nanocrystalline diamond films to examine the functional adhesion strength between the diamond films and the silicon substrates. The nanocrystalline diamond/silicon wafer systems demonstrated very good film adhesion (LCN ≈ 3.1 — 3.4 N). A CDC biofilm reactor was utilized to incubate and grow Pseudomonas fluorescens on the surfaces of the nanocrystalline diamond thin films and stainless steel coupons. Quantitative data showed that bacterial attachment on the nanocrystalline diamond thin films was quite significant and comparable to that on stainless steel surfaces. This work suggests that nanocrystalline diamond thin films are good candidate materials for biomedical implants but are susceptible to microbial colonization.