Biological sensing with nano-bio interface systems
Abstract
Nanoelectrode arrays comprised of carbon-based nanomaterials offer a high-performance platform for electrochemically sensing numerous biomolecular agents due to their unique mechanical, electrical, and chemical properties. Metallic nanoparticles intertwined with carbon-based nanomaterials have shown great promise in electrochemical biosensing--providing some of the best performance characteristics to date. However, the concomitance of a scalable fabrication technique, robust biofunctionalization scheme, and enhanced performance ( i.e., low detection limit and wide linear sensing range) remains to be realized--creating a gap between fundamental research and commercial viability. This dissertation provides a bridge between biosensor research and commercial feasibility by detailing a bottom-up approach to nanoelectrode array fabrication that is scalable and suitable for a wide variety of biological sensing applications. Both the nanofabrication and biofunctionalization protocols are altered and analyzed in distinct ways in order to improve performance and scalability. First, arrays of single-walled carbon nanotubes (SWCNTs) are grown via microwave plasma enhanced chemical vapor deposition from a template of porous anodic alumina developed from a silicon wafer. Au coated Pd nanocubes and Pt nanospheres are electrochemically deposited at SWCNT defect sites to enhance electro-reactivity. The electrodes are converted into glucose biosensors by immobilizing the enzyme glucose oxidase (GOx) via covalent thiol linking and non-covalent drop coat methods. These initial SWCNT/metal nanoparticle hybrid sensors provide fascinating results--enabling some of the most highly sensitive glucose sensing to date, however, a comprehensive understanding of the relationship between the nanofabrication/biofunctionalization protocols and biosensor performance is still lacking. In an effort to elucidate the tradeoffs among kinetics, mass transport, and charge transport, the SWCNT/Pt nanosphere biosensors are computationally modeled in an enzymatic biosensing scenario. These in silico results, corroborated experimentally, demonstrate how the Pt nanosphere density along the SWCNTs can substantially alter the biosensor detection limit, linear sense range, and sensitivity. These results paved the way for subsequent comparative studies were the material, shape, size, and density of biosensor nanostructures are analyzed side-by-side. First, Pd nanocubes and Pt nanospheres electrodeposited on SWCNTs are comparatively tested in a glutamate biosensing environment. Additionally, the density and size of Pt facets associated with the Pt nanoparticles electrodeposited on the SWCNT arrays is also currently being studied. Next, the effects of both short- and long-chain enzyme-conjugated self-assembled monolayers immobilized on Au nanoelectrode arrays are electrochemically tested and compared. Finally, in a culminating work, the size and density of Pt nanoparticles electrodeposited on graphene petal nanosheets (GPNs) are modulated to maximize biosensor performance. The fabrication of the Pt-GPN biosensors does not require lithograpy steps nor metal catalyst patterning techniques while the electrodeposition of GOx via the electrically conductive polymer Poly(3,4-ethylenedioxythiophene) (PEDOT) permits sensitive and selective glucose sensing for extended periods of time (> 1 month). In addition, research is underway to incorporate these nanostructured electrode into lab-on-a-chip platforms that will potentially enable multiplexed monitoring of numerous analytes associated with medicine, agriculture, food safety, and national security.
Degree
Ph.D.
Advisors
Fisher, Purdue University.
Subject Area
Engineering|Biomedical engineering|Nanotechnology
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