| Currently, 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 the bioapplications. In this study, we firstly prepared four kind of gold nanorods with different ratios of long and short radius, then characterized them using UV-Vis spectroscopy, TEM and Fluorescence Correlation Spectroscopy (FCS). Furthermore, we used 17 nm GNPs as a model, and modified them with six thiol compounds including glutathione, mercaptopropionic acid (MPA), cysteine, cystamine, dihydrolipoic acid (DHLA) and thiol-ended polyethylene glycol (PEG-SH) via Au-S bond. We systematically investigated the effects of thiol ligands, pH and salt concentrations of solutions on colloidal stability to GNPs using UV-Vis absorption spectroscopy, fluorescence correlation spectroscopy (FCS) and Zeta potential instrument. We found that GNPs modified with PEG-SH were the most stable in aqueous solution compared to other thiol compounds. Based on the results above, we developed a simple and efficient approach for modification of GNPs using a mixture of PEG-SH and MPA as ligands. These bi-ligands modified GNPs were facilely conjugated to antibody using EDC (1-ethyl-3-(3-dimethylaminopropyl) carbodiimide) and N-hydroxysulfo-succinimide (Sulfo-NHS) as linkage reagents. We conjugated GNPs to epidermal growth factor receptor (EGFR) antibodies, and successfully used the antibody-GNPs conjugates as targeting probes for imaging of cancer cells using the illumination of dark field. Compared to current methods for modification and conjugation of GNPs, our method described here showed simple, low-cost, and have potential applications in bioassays and cancer diagnostics and studies. |
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