Colloidal Stability of Gold Nanoparticles Modified with Thiol Compounds: Bioconjugation and Application in Cancer Cell Imaging

Abstract

Gold nanoparticles (GNPs) are attractive alternative optical probes and good biocompatible materials due to their special physical and chemical properties. However, GNPs have a tendency to aggregate particularly in the presence of high salts and certain biological molecules such as nucleic acids and proteins. How to improve the stability of GNPs and their bioconjugates in aqueous solution is a critical issue in bioapplications. In this study, we first synthesized 17 nm GNPs in aqueous solution and then modified them with six thiol compounds, including glutathione, mercaptopropionic acid (MPA), cysteine, cystamine, dihydrolipoic acid, and thiol-ending polyethylene glycol (PEG-SH), via a Au-S bond. We systematically investigated the effects of the thiol ligands, buffer pH, and salt concentrations of the solutions on the colloidal stability of GNPs using UV-vis absorption spectroscopy. We found that GNPs modified with PEG-SH were the most stable in aqueous solution compared to other thiol compounds. On the basis of the above results, we developed a simple and efficient approach for modification of GNPs using a mixture of PEG-SH and MPA as ligands. These biligand-modified GNPs were facilely conjugated to antibody using 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide and N-hydroxysulfosuccinimide as linkage reagents. We conjugated GNPs to epidermal growth factor receptor antibodies and successfully used the antibody-GNP conjugates as targeting probes for imaging of cancer cells using the illumination of a dark field. Compared to current methods for modification and conjugation of GNPs, our method described here is simple, has a low cost, and has potential applications in bioassays and cancer diagnostics and studies.

Synthesis of oligo(lactose)-based thiols and their self-assembly onto gold surfaces

“…For example, functionalization with nucleic acids or proteins may destabilize AuNPs, and to improve the colloidal stability the biospecific molecule is mixed with filler molecules providing both steric stabilization and biocompatibility. [12][13][14][15] Oligo(ethylene) glycols (OEGs) are commonly used for steric stabilization of particles, [16,17] including stabilization of liposomes used as drug delivery vehicles, where they also prevent the triggering of immune responses. [18] As an alternative, we have synthesized the oligosaccharides 1-3 ( Figure 1) which presumably are rod-like [19] Immobilization of thiol compounds on gold surfaces into self-assembled monolayers (SAMs) is widely used to prepare well-defined and versatile model surfaces for studies of protein adsorption and biofouling.…”

Immunoassay for Human IgG Using Antibody-functionalized Silver Nanoparticles

“…Moreover, polyclonal antibodies are more stable over a broad salt concentration and pH. 40,42 The coupling of anti-hIgG to AgNPs was accomplished using mercaptosuccinic acid (MSA). The sulfhydryl group of MSA binds covalently to the metal, whereas its carboxylic group interacts electrostatically with the positively charged moieties such as ammonium present in the antibody.…”

“…However, this conjugation method proved to be effective when used in the development of immunoassays employing metal nanoparticles, 13 and no aggregation was observed before addition of NaClO4. [42][43][44] Additionally, the effect of anti-hIgG concentration was investigated in the range of 150 and 750 ng mL -1 . The best performance was observed using 150 ng mL -1 anti-hIgG.…”

Enhanced Radiation Therapy of Gold Nanoparticles in Liver Cancer

“…Stability of bio-conjugates of GNPs in aqueous solutions is a critical issue in bio-applications. In our study, we found PEG-SH modified GNPs to be more stable compared to other thiol-compounds in aqueous solutions (e.g., cysteine and homocysteine) [52]. We assessed the stability of GNPs in plasma, cellular uptake and their intracellular distribution, cytotoxicity, and radiation therapeutic effect under radiation by 137 Cs at doses of 0-4 Gy in two different cell lines.…”