School of Physics - Theses
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ItemSurface modification of nanoporous anodic alumina for biomedical applications( 2015)The development of new nanoporous materials promise advances in many chemical, medical, biological and environmental industries. Nanoporous anodic aluminum oxide (AAO) is a porous structure with tunable chemical and physical properties, which can be easily fabricated with a straight-forward electrochemical process. AAO membranes are among the most promising platforms for various applications due to their robustness, uniform and narrow porous structure, and their scalable fabrication. However, practical biomedical applications of AAO are scarce due to poor (bio-)chemical stability of the oxide. Surface modification of AAO membranes is used to improve various properties of the AAO material, such as chemical stability, biocompatibility and functionality. Surface modification opens up new opportunities for advanced applications, especially for biomedical application that have a high demand for functional membranes. Functional nanoporous membranes can be used in catalysis, sensors and filters which are commonly used in biology and chemistry. For past few decades, different approaches have been taken to improve the surface properties of AAO, mostly resulted to limited improvement in stability and non-cytotoxicity. Due to the confined space and high aspect ratio of the nanopores, most of the available techniques failed to provide a conformal and protective surface modification for AAO structure. To find a solution for this challenge, I set out to find a better surface treatment for AAO, one that would be conformal, biocompatible, resistant to corrosion and readily functionalized. In this thesis I report on a novel method to fabricate composite nanoporous nanodiamond and diamond-like carbon coated alumina nanomaterials by chemical vapor deposition. I demonstrate that these hybrid nanomaterials exhibit multiple functionalities, such as high surface area, quasi-ordered nanopore structure, tunable surface chemistry and electrical conductivity, excellent biological, chemical and corrosion resistance. In particular I report on the synthesis of ultrathin sp3-bonded carbon layers (2-5 nm) into three-dimensional nanoporous materials that produces a conformal, impermeable, protecting carbon layer over the whole surface of the nanoporous structure. The thin yet perfect coating of the membrane confers the chemical stability (1 < pH < 14) and biocompatibility on the nanoporous alumina. The modified nanoporous membranes exhibit biochemical properties comparable to diamond. These novel nanoporous materials have a great potential to be used in different chemical (filters, catalysis and sensors) and biomedical applications that require materials that need to be biocompatible or withstand extreme corrosive environments. In a demonstration of the potential utility of these materials, I have modified their surfaces to realize a new platform for biosensing. The platform is based on a combination of a sensor and a flow-through nanoporous filter in a single device, allowing effective detection and capture of trace concentrations of DNA in large volumes. A truly “ultra-high density 3D DNA array” is obtained using chemical functionalization of the modified nanoporous membranes. The fabricated sensors demonstrate unique broad-range detection sensitivity, which is by several orders of magnitudes better than the commercial gene arrays and other flat-based DNA arrays. In addition, single-molecules are detected inside of the nanopores using depth profiling in confocal microscopy - which is to our knowledge the first demonstration of single-molecule detection using nanoporous alumina membranes.