Effects of Ligand Coordination Number and Surface Curvature on the Stability of Gold Nanoparticles in Aqueous Solutions

• Published in: Langmuir Vol. 25; no. 18; pp. 10604 - 10611
• Main Authors: Mei, Bing C, Oh, Eunkeu, Susumu, Kimihiro, Farrell, Dorothy, Mountziaris, T. J, Mattoussi, Hedi
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15-09-2009
• Subjects: Chemistry; Colloidal state and disperse state; Colloids - chemistry; Colloids: Surfactants and Self-Assembly, Dispersions, Emulsions, Foams; Dithiothreitol - chemistry; Exact sciences and technology; General and physical chemistry; Gold - chemistry; Ligands; Metal Nanoparticles - chemistry; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Salts - chemistry; Sodium Cyanide - chemistry; Solutions; Sulfhydryl Compounds; Surface physical chemistry; Resistance; Gold; Stability; Packing; Sodium; Nanoparticle; Transition metal; Cyanides; Aqueous solution; Curvature; Density; Nanocrystal
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la901423z

The colloidal stability of gold nanoparticles (AuNPs) cap-exchanged with either monothiol- or dithiolane-terminated PEG-OCH3 ligands was investigated. Three distinct aspects were explored: (1) effects of excess salt concentration; (2) ligation competition by dithiothreitol (DTT); and (3) resistance to sodium cyanide digestion. We found that overall ligands presenting higher coordination numbers (dithiolane) exhibit much better stability to excess added salt and against competition from DTT compared to their monodentate counterparts. Resistance to NaCN digestion indicated that there is a balance between coordination number and density of ligand packing on the NP surface. For smaller NPs, where a larger surface curvature reduces the ligand packing density, a higher coordination number is clearly beneficial. In comparison, a higher ligand density allowed by the smaller curvature for larger nanocrystals makes monothiol−PEG-capped NPs more resistant to cyanide digestion. The present study indicates that balance between the coordination number and surface packing density is crucial to enhancing the colloidal stability of AuNPs.