353— Interfacial Interaction of Amyloid Beta Peptide 1-40 with ThT

The amyloid beta peptide 1-40 (Ab1-40) was prepared over nano-gold colloidal surfaces together with Thioflavin T (ThT) dye as a fluorophore. The fluorescence assay of ThT displayed two different types of fluorescence bands: 1) mainly originating from free-ThT and 2) ThT significantly interacted with Ab1-40. The ThT directly interacted with Ab1-40 adsorbed over the gold colloidal surface. Significant evidence supporting that Ab1-40 has higher binding affinity than a gold colloidal surface was obtained. A series of studies on fluorescence decay time were collected at various pH’s ranging, from pH 1 to pH 12, and with several gold colloidal sizes ranging from 10 nm to 100 nm. It was concluded that ThT attached to either 22Glu or 23Asp of the Ab1-40 through an electrostatic interaction between adjacent Ab1-40 monomers, as Ab1-40 proceeds a folding conformational change. The spacing between adjacent Ab1-40 monomers was increased for gold colloidal sizes of 50 nm and above. An identification of the ThT attachment site in Ab1-40 simultaneously confirmed that the hydrophilic segment of Ab1-40 was used in binding to the gold colloidal surface and hydrophilic site of Ab1-40, networking with the other Ab1-40 adsorbed on the gold colloidal surface.