title: Gold nanoparticles decorated with oligo(ethylene glycol) thiols: surface charges and interactions with proteins in solution.
abstract: We have studied oligo(ethylene glycol) (OEG) thiol self-assembled monolayer (SAM) coated gold nanoparticles (AuOEG) and their interactions with proteins in solutions using electrophoretic and dynamic light scattering (ELS and DLS). The results are compared with poly(ethylene glycol) (PEG) thiol coated AuNPs (AuPEG). We show that both AuOEG and AuPEG particles carry a low net negative charge and are very stable (remaining so for more than one year), but long-term aging or dialysis can reduce the stability. If the decorated AuNPs are mixed with bovine serum albumin (BSA), both effective size and zeta-potential of the AuNPs remain unchanged, indicating no adsorption of BSA to the colloid surface. However, when mixed with lysozyme, zeta-potential values increase with protein concentrations and lead to a charge inversion, indicating adsorption of lysozyme to the colloid surface. The colloidal solutions of AuOEG become unstable near zero charge, indicated by a cluster peak in the DLS measurements. The AuPEG solutions show similar charge inversion upon addition of lysozyme, but the solutions are stable under all experimental conditions, presumably because of the strong steric effect of PEG. Washing the protein bound colloids by centrifugation can remove only part of the adsorbed lysozyme molecules indicating that a few proteins adsorb strongly to the colloids. The effective charge inversion and rather strongly bound lysozyme on the colloid surface may suggest that in addition to the charges formed at the SAM-water interface, there are defects on the surface of the colloid, which are accessible to the proteins. The results of this study of surface charge, and stability shed light on the interaction with proteins of SAM coated AuNPs and their applications.
authors.affiliation: Institut für Angewandte Physik, Universität Tübingen, Auf der Morgenstelle 10, D-72076 Tübingen, Germany.
authors.forename: Moritz
authors.initials: M
authors.lastname: Schollbach
authors.affiliation: Institut für Angewandte Physik, Universität Tübingen, Auf der Morgenstelle 10, D-72076 Tübingen, Germany. Electronic address: fajun.zhang@uni-tuebingen.de.
authors.forename: Fajun
authors.initials: F
authors.lastname: Zhang
authors.affiliation: Institut für Angewandte Physik, Universität Tübingen, Auf der Morgenstelle 10, D-72076 Tübingen, Germany.
authors.forename: Felix
authors.initials: F
authors.lastname: Roosen-Runge
authors.affiliation: STFC, ISIS, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0OX, United Kingdom.
authors.forename: Maximilian W A
authors.initials: MW
authors.lastname: Skoda
authors.affiliation: Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Mansfield Road OX1 3TA, United Kingdom.
authors.forename: Robert M J
authors.initials: RM
authors.lastname: Jacobs
authors.affiliation: Institut für Angewandte Physik, Universität Tübingen, Auf der Morgenstelle 10, D-72076 Tübingen, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Schreiber
mesh_terms: D003102:Colloids; D005026:Ethylene Glycols / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D053768:Metal Nanoparticles / Q000737:chemistry*; D011506:Proteins / Q000737:chemistry*; D012996:Solutions; D013056:Spectrophotometry, Ultraviolet; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D003102:Colloids; D005026:Ethylene Glycols; D011506:Proteins; D012996:Solutions; D013438:Sulfhydryl Compounds; D006046:Gold
keywords: DLS; Gold nanoparticles; Oligo(ethylene glycol) thiol; Self-assembled monolayer; UV–visible spectroscopy; Zeta-potential