Physical and Optical Characterization of Anodized Aluminum-Tantalum Thin Films for use in Thin Film Diagnostics

• Author / Creator

  Nickel, Matthew R

• Thin film diagnostics have been proposed as a solution to the growing need for point-of-care diagnostic tests. Diagnostics based on anodized aluminum-tantalum thin films use interference colours to detect the adsorption of protein layers on a surface. The purpose of this work was to develop a stronger understanding of thin film diagnostics based on anodized aluminum-tantalum thin films with respect to: 1) deposition parameters of the metallic films and their effect on the optical properties, microstructure and sensitivity when developed for an immunoassay, 2) anodization parameters and their effect on the optical properties, microstructure and sensitivity when developed for an immunoassay, 3) effect of antigen size and surface density on the thin film interference colours, and 4) demonstration of a new binding technology to aluminum oxides to expand the use of these films for detecting other antigen-antibody pairs. Deposition of the tantalum and aluminum films is done using magnetron sputtering techniques. Adjusting the microstructure of the deposited tantalum films by changing the sputtering gas pressure had an effect on the optical reflectance, however no effects were found on the sensitivity of detecting adsorbed protein layers. The microstructure of the deposited aluminum films had minimal effect on the optical properties (refractive index and extinction coefficient) of the oxidized films after anodization. Sputtering parameters that achieved smoother, homogeneous films after anodization tended to show higher sensitivity to detecting adsorbed proteins. The electrolyte and voltage during anodization had significant effects on the optical properties, microstructure and sensitivity. Oxalic acid additive to a phosphoric acid bath was found to significantly improve film homogeneity and reduce surface roughness and pore size of the anodic alumina layer. This, in turn, was found to improve the sensitivity for detecting adsorbed protein and improve the tunability of the optical properties over films anodized strictly in phosphoric acid. Methods were also discovered, using sulphuric acid or a voltage-step procedure, to tailor the pore size at the surface while simultaneously adjusting the optical properties of the anodic film. Antigen surface density was also found to have an effect on sensitivity for antibody assays. Spacing of an antigen on the film surface showed improved detection of a polyclonal antibody at lower concentrations. Finally, a new binding technology for proteins to aluminum oxides was applied to these diagnostics to expand the application for detecting secondary antibodies or antibodies for the Zika viral protein, non-structural protein 1 (NS1). Overall, these films showed significant tunability and high sensitivity, making them very useful for a variety of medical or research applications.

• Subjects / Keywords

  • anodized aluminum
  • biomedical
  • point-of-care diagnostics
  • thin film interference
  • nanostructured thin films

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R30P0X670

• License

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