Development of Biosensors to Monitor the Interaction of Small Molecules with Amyloidogenic Proteins using Optical and Electrochemical Methods

Amyloidogenic protein fibrils are well known pathological hallmark of neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). The Amyloid Cascade Hypothesis attributes the onset and progression of AD to an imbalance in amyloid-beta (Abeta). In PD, a definitive diagnosis of Parkinson's disease can be confirmed only by post mortem examination of the patient's substantia nigra for the presence of Lewy bodies, mainly comprised of alpha-synuclein (a-S). As the toxicity in these neurodegenerative diseases is highly correlated with the formation of soluble oligomers from their corresponding proteins, a strategy to inhibit the aggregation of Abeta and a-S may help to ameliorate AD and PD respectively (Chapter 1). Herein, we review the fundamentals of electrochemistry (Chapter 2) before demonstrating the use of electrochemical techniques, acoustic wave sensor and BiacoreX surface plasmon resonance (SPR) to characterize the aggregation of Abeta (Chapter 3). We have shown that amyloid aggregation could be monitored through these label-free methods and clioquinol (CQ) inhibits the progression of aggregation. We further increased the throughput of monitored small molecules and Abeta interactions through the use of SPR imaging (SPRi) (Chapter 4) and LED-interferometric reflective imaging sensor (LED-IRIS) (Chapter 5). These studies showed that epigallocatechin gallate (EGCG) modulates the Abeta aggregation pathway to form beta-sheet absent aggregates while certain metal ions generally accelerate the Abeta aggregation process to form thick mature fibrils. These results are supported by Thioflavin T (ThT) and transmission electron microscopy (TEM) studies.We then studied the effects of CQ on a-S (Chapter 6) using electrochemical techniques and spectroscopic dyes such as ThT and Congo Red. Both electrochemical and spectroscopic studies showed that Cu(II) accelerated the fibril formation of a-S, while CQ inhibited such activity. This electrochemical analysis was further modified to include an optical screening test on the same transduction platform by utilizing nanosphere lithography (NSL) (Chapter 7). Complemented by Localized-SPR, SPRi, TEM and ThT studies, it was found that dense and unstructured amorphous a-S aggregates were induced by EGCG, while beta-sheet-rich and compact a-S mesh-networks were promoted by Cu(II) ions, in agreement with previous results.Ph.D