Au nanoparticle-modified DNA sensor based on simultaneous electrochemical impedance spectroscopy and localized surface plasmon resonance.

Electrochemical impedance spectroscopy (EIS) and localized surface plasmon resonance (LSPR) were performed on the same Au nanoparticle (AuNP)-modified indium tin oxide (ITO) coated glass surfaces. Cyclic voltammetry was applied to electrodeposit AuNPs on ITO surface directly. The surface plasmon band characterization of AuNPs was initially studied by controlling the electrodeposition conditions. It was found that the size of AuNP clusters was significantly affected by the applied potential and KCl concentration in solution. The dual-detection platform was applied to detect DNA hybridization related to a specific point mutation in apolipoprotein E gene (ApoE), which was related to the progression of Alzheimer's disease. The preliminary results facilitate the development of a versatile biosensor that can be easily miniaturized and integrated into a high-throughput diagnostic device.

Surface plasmon resonance imaging of amyloid-ß aggregation kinetics in the presence of epigallocatechin gallate and metals.

A number of human protein misfolding disorders, including Alzheimer's disease (AD), are closely related to the accumulation of ß-sheet-rich amyloid fibrils or aggregates. Neuronal toxicity in AD has been linked to the interactions of amyloid-ß (Aß) with metals, especially Zn(2+), Cu(2+), and Fe(3+), which leads to the production of reactive oxygen species. Nucleation-dependent Aß aggregation, or "seeding", is thought to propagate fibril formation. In this surface plasmon resonance imaging (SPRi) study, we have shown that the fibril seeds formed with the incubation of Aß in the presence of metals are better at promoting monomer elongation compared to Aß alone or in the presence of a well-described polyphenol, (-)-epigallocatechin-3-gallate (EGCG). This is a novel attempt to simultaneously monitor the effects of multiple modulators on fibril elongation using a single chip. EGCG was shown in transmission electron microscopy (TEM) and thioflavin T (ThT) studies to promote the formation of off-pathway, highly stable unstructured oligomers, supporting the SPRi results. These findings suggest that SPRi provides a promising platform as a screening tool for small molecules that can affect the aggregation pathways in neurodegenerative diseases.