Hybrid Conjugates Formed between Gold Nanoparticles and an Amyloidogenic Diphenylalanine-Cysteine Peptide

We investigated the effect of gold nanoparticles (AuNPs) on the aggregation of a CFF (C=cysteine; F=phenylalanine) tripeptide (derived from Aβ peptide) in aqueous medium. Special attention was dedicated to the role of AuNPs as inducers and inhibitors during nucleation kinetics and the structure of the resulting scaffolds was carefully investigated. At millimolar concentrations, the tripeptide was found to form β-sheet structures organized into long filaments. Spectral signatures and topography of the filaments were studied by Raman spectroscopy and atomic force microscopy (AFM), revealing that conjugation to AuNPs not only stabilizes the system, but also inhibit or enhance amyloid-like features depending on the synthesis route used in the preparation of AuNPs. Sodium borohydride (NaBH4) mediated synthesis of AuNPs gave rise to a strong absorption peak close to 520 nm, indicating that AuNPs were dispersed, independently of the peptide concentration added in the reaction. However, when the peptide/gold salt mixture was heated at 60 °C, AuNPs and AuNP-decorated filaments were both formed in solution and the fractions of which population were found to be dependent on the [HAuCl4]/[CFF] ratio, as illustrated by TEM images. In addition, the insertion of AuNPs at the surface of CFF nanostructures can promote electron transfer from the metallic nanoparticles to the CFF surface, creating an n-type semiconductor, and causing a peak shift of the phenylalanine absorption band.