I: Thin-Film Nanoporous Anodic Alumina For Nanobiotechnology Ii: Microscale Cd4+ Cell Biosensor With Single-Cell Resolution For Diagnosis Of Hiv Infection

Abstract

Two research topics were presented in this dissertation. The first topic focused on nanoporous anodic alumina thin films and their applications in nanobiotechnology. It discussed in details the fabrication and the characterizations of nanoporous anodic alumina thin films on silicon substrates. Two methods were presented for fabricating freestanding PAA thin films with open pores. In the first method, an alumina thin film was fabricated on a Si3N4-coated silicon substrate. A partly freestanding structure was achieved by removing the silicon substrates using KOH anisotropic etch. The second method, named as "double-layer anodization", was developed for fabricating partly or fully freestanding alumina thin films by utilizing a sacrificial metal layer. The confined diffusion of small organic molecules in alumina nanopores was investigated. The diffusion system was built upon the silicon-based freestanding alumina thin film. The molecular diffusion in alumina pores was modeled as a one-dimensional Fickian flow, based on which the diffusion dynamics was characterized. A novel DNA biosensor utilizing the large surface area of alumina films was developed. The device was based on a metal-alumina-metal vertical structure. The top and bottom metal films served as electrodes while the sandwiched alumina membrane served as a porous dielectric layer. Single-stranded DNA oligonucleotides were attached to the sidewalls of the alumina pores through chemical modifications. The DNA hybridization process was sensed by measuring the impedance spectrum of the alumina membrane between the two electrodes. The second topic was the research of a cell biosensor for the precise quantification of human CD4+ cells, orientated for the development of affordable point-of-care diagnostic tools for analyzing the HIV-infection status of AIDS patients. With this motivation, an impedance biosensor was developed, based on an array of cell-sized working electrode pixels. Each electrode pixels was able to independently detect the existence of one single cell on the electrode surface. The cell counting was digitalized by the electrode pixelation, being independent of the cell concentration. With this sensor, the detection of CD4+ cells at single-cell resolution was demonstrated.