Gold nanoparticles decorated with oligo(ethylene glycol) thiols: Surface charges and interactions with proteins in solution

• Published in: Journal of colloid and interface science 2014-07, Vol.426 (426), p.31-38
• Main Authors: Schollbach, Moritz, Zhang, Fajun, Roosen-Runge, Felix, Skoda, Maximilian W.A., Jacobs, Robert M.J., Schreiber, Frank
• Format: Article
• Language: English
• Subjects: Charge; Chemistry; Colloidal state and disperse state; Colloids; DLS; Ethylene Glycols - chemistry; Exact sciences and technology; General and physical chemistry; Glycols; Gold - chemistry; Gold nanoparticles; Hydrogen-Ion Concentration; Inversions; Lysozyme; Metal Nanoparticles - chemistry; Oligo(ethylene glycol) thiol; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Proteins; Proteins - chemistry; Self-assembled monolayer; Solutions; Spectrophotometry, Ultraviolet; Sulfhydryl Compounds - chemistry; Surface chemistry; Surface Properties; Thiols; UV–visible spectroscopy; Zeta-potential
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2014.03.052

[Display omitted] •We examine the long-term stability of OEG coated AuNPs in solution.•We study the interaction of these colloids with proteins.•Addition of negatively charged protein, such as BSA, stabilizes the system.•Addition of positively charged protein, such as lysozyme, leads to a reentrant condensation.•The mechanism of reentrant condensation is an effective charge inversion of the colloids. 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.