Functionalization of gold nanoparticles with amino acid, beta-amyloid peptides and fragment

Gold nanoparticles (Au NPs) were functionalized by cysteine (Cys), beta-amyloid peptides (Cys(0)Abeta(1-28), Cys(0)Abeta(1-40), Abeta(1-42)) and a pentapeptide fragment (Leu-Pro-Phe-Phe-Asp-OH (LPFFD-OH)). Optical absorption spectra of these systems were recorded and the plasmon resonance maximum values (lambda(max)) of the UV-vis spectra together with the transmission electron microscopy (TEM) images were also analysed. Both TEM images and the appearance of a new absorption band between approximately 720 and 750 nm in the visible spectra of the Au-cysteine and Au-LPFFD-OH systems most probably indicate that upon addition of these molecules to Au NPs-containing aqueous dispersions formation of aggregates is occurred. The wavelength shift between the two observed absorption bands in cysteine- and pentapeptide-modified Au NPs systems are Deltalambda=185 and 193 nm, respectively. These results suggest that the monodisperse spherical gold nanoparticles were arranged to chained structure due to the effect of these molecules. For confirmation of the binding of citrate and cysteine onto the plasmonic metal surface (1)H NMR measurements were also performed. (1)H NMR results may suggest that the citrate layer on the metal surface is replaced by cysteine leading to a formation of organic double layer structure. In the presence of beta-amyloid peptides the aggregation was not observed, especially in the Au-Cys(0)Abeta(1-40) and Au-Abeta(1-42) systems, however compared to the cysteine or LPFFD-OH-containing gold dispersion with Cys(0)Abeta(1-28) measurable less aggregation were occurred. The spectral parameters clearly suggest that Abeta(1-42) can attach or bind to the surface of gold nanoparticles via both the apolar and the N-donors containing side-chains of amino acids and no aggregation in the colloidal gold dispersion was observed.