New nanomaterials: amyloid fibrils from waste proteins
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosopy
The current landscape of nanotechnology has focussed attention on materials that self-assemble. The search for such materials has unsurprisingly led to the biological world, where functional nanoscale biomolecular assemblies are in abundance. Amyloid fibrils are one such self-assembling biological structure, formed when native proteins misfold into insoluble fibrous quaternary structures. This research has explored the use of amyloid fibrils formed from waste proteins, namely crude crystallin proteins from fish eye lenses, as biological nanowires. The use of amyloid fibrils as nanowires was investigated by examining the ability to control their dimensions and arrangement, along with analysis of their properties, such as stability and conductivity. TEM and AFM studies on the model amyloid forming protein, bovine insulin, showed that a number of fibril length distributions can be achieved, by systematically altering fibril growth and storage conditions. Although the same set of conditions cannot be directly applied to crystallin fibrils, these fibrils can also be produced on a range of length scales. Amyloid fibrils can be manipulated and aligned in a controlled manner by dielectrophoresis; this tool could later be used to incorporate amyloid fibrils into a biosensing or bioelectronics device. Dielectrophoresis was also used to immobilise crystallin fibrils between electrode pairs, in order to investigate the conductivity of small numbers of fibrils. These experiments complemented work carried out on the conductivity of amyloid fibril networks, using fabricated interdigitated electrodes. In the unmodified state, amyloid fibrils formed from bovine insulin, fungal hydrophobins, and crude crystallins were all shown to have low conductivity, with current values in the range of 10⁻⁸–10⁻¹⁰ A recorded at bias voltages of 0–2 V. Amyloid fibrils were used as a template for the synthesis of conductive nanowires, by modification with the conducting polymers polyaniline and polypyrrole, increasing conductivity by one and four orders of magnitude respectively. The functionalisation of fibrils with glucose oxidase enabled the creation of a very simple glucose sensing device. This device, consisting of a gold electrode modified with the glucose oxidase functionalised fibrils, showed an electrochemical response in the presence of glucose and the mediator FcOH. Future work is necessary to optimise the use of amyloid fibrils in this way; however, this study confirms a role for amyloid fibrils from a low cost source in bionanotechnology.