Gold nanoparticles (Au NPs) were functionalized by cysteine (Cys), beta-amyloid peptides
(Cys(0) A beta(1-28), Cys(0)A beta(1-40), A beta(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 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 A?, 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 H-1 NMR measurements
were also performed. 1H 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)A(1-40) and Au-A 42 systems, however compared to the cysteine or LPFFD-OH-containing
gold dispersion with Cys(0)A beta(1-28) measurable less aggregation were occurred.
The spectral parameters clearly suggest that A beta(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. (C)
2010 Elsevier ay. All rights reserved.