The physicochemical properties of gold nanoparticles (GNPs) functionalized with peptides and N-methylated peptides were studied with respect to their interaction with beta-amyloid (1-42). Peptides with sequences of CGGIGLMVG and CGGGGGIGLMVG linked with GNPs of an average diameter of 13 nm were employed for this study. The peptide-GNPs were found to be soluble and dispersed at pH 7.4 in a sodium phosphate aqueous buffer solution. The resonance spectra of each peptide coated GNP was measured in the absence and presence of beta-amyloid (1-42). The difference in the intensity of the lambda(max) of the resonance absorption bands was attributed to the interaction of the functionalized GNPs with the protein. Particles bearing the CGGGGGIGLMVG sequence exhibited the largest change in lambda(max) intensity; the prevention of fibril formation and inhibition of cytotoxicity was also examined.