Interactions between Oligoethylene Glycol-Capped AuNPs and Attached Peptides Control Peptide Structure.

Peptide-functionalized nanoparticles (NPs) often rely on a well-defined peptide structure to function. Here, we report the attachment of model peptides to the ligand shell of AuNPs passivated with oligoethylene glycol (OEG). Specifically, peptides containing the repeating (LLKK)n motif plus either one or two reactive functional groups were covalently linked to OEG-capped, ∼5 nm AuNPs via the Cu+-catalyzed azide-alkyne cycloaddition reaction. This work builds on a previous study from our group in which an (LLKK)n peptide having two reactive functional groups was considered. Peptide attachment was confirmed by FTIR spectroscopy. Amino acid analysis was used to determine that 3-4 peptides were immobilized per AuNP. Circular dichroism spectroscopy revealed a structural change from random coil in solution to α-helical upon attachment to OEG-capped AuNPs. The key result of this study is that the nature of the capping layer on the AuNP surface influences peptide structure to a significant degree. Other important findings resulting from this work are that the AuNP-peptide conjugates reported here are water soluble and that the long axis of the helical peptides is oriented tangent to the AuNP surface. The latter point is important for applications involving biorecognition.