Rational and combinatorial design of peptide capping ligands for gold nanoparticles
Authors: Irshad Hussain
Raphaël Lévy
David G Fernig
Mathias Brust
Richard J Nichols
Nguyen T K Thanh
David J Schiffrin
R Christopher Doty
Journal: Journal of the American Chemical Society (2004)
Discipline: CHEMISTRY
Keywords: Protein folding; Peptide ligand; Gold nanoparticles; Stability; Water-soluble
Affiliations: Contribution from the Center for Nanoscale Science, School of Biological Sciences, Bioscience Building, and Department of Chemistry, University of Liverpool, Liverpool L69 7ZB, U.K.

Abstract:  Based on protein folding considerations, a pentapeptide ligand, CALNN, which converts citrate-stabilized gold nanoparticles into extremely stable, water-soluble gold nanoparticles with some chemical properties analogous to those of proteins, has been designed. These peptide-capped gold nanoparticles can be freeze-dried and stored as powders that can be subsequently redissolved to yield stable aqueous dispersions. Filtration, size-exclusion chromatography, ion-exchange chromatography, electrophoresis, and centrifugation can be applied to these particles. The effect of 58 different peptide sequences on the electrolyte-induced aggregation of the nanoparticles was studied. The stabilities conferred by these peptide ligands depended on their length, hydrophobicity, and charge and in some cases resulted in further improved stability compared with CALNN, yielding detailed design criteria for peptide capping ligands. A simple strategy for the introduction of recognition groups is proposed and demonstrated with biotin and Strep-tag II. 

Retracted: No

PubPeer comments:
 Supporting Information appears to have images which overlap (S9-S58). ![file] , 
 Figures S9 (left) and S58 (right) (Supporting information) appears to have images which overlap. ![file] Figure S9. Effect of peptide length. Absorbance spectra of CALNN-capped gold nanoparticles in increasing NaCl concentrations Figure S58. New design. Absorbance spectra of CCVVVT-capped gold nanoparticles in increasing NaCl concentrations Two different experiments with different polymers and yet an almost identical uv spectrum (see the GIF). How is it possible ? ![file] , 
 Response from the senior author, on whom responsibility rests in one way or another. The peptides are oligomers, not polymers. The plasmon resonance is sensitive to the size of the nanoparticles and the refractive index of the local environment. This experiment presents the evolution of the plasmon resonance as a function of ionic strength for two peptides that form a monolayer on gold nanoparticles. Since the gold nanoparticle solution is the same (the peptides are added after synthesis), for two peptide monolayers that provide similar stability, one would expect very similar spectra. As the gif helpfully shared by Babiana Flabellifolia shows, these spectra are in fact very different, in particular at high ionic strength with CCVVVT (right) providing higher stability than the spectra on the left. Incidentally, Babiana Flabellifolia made a mistake : the UV-vis presented above as CALNN fig S9 is not CALNN fig S9, it is CALN fig S8. CALNN-capped gold nanoparticles are more stable and therefore the similarity is in fact higher between CALNN (S9) and CCVVVT (S58). ,