Gold nanoparticles: synthesis, characterization, and bioconjugation

Abstract

Gold nanoparticles (Au NPs) with diameters ranging between 4-150 nm have been synthesized in water. The strong reducing agent sodium borohydride (NaBH4) was used to produce small Au NPs with diameter about 4 +_1 nm. 15 and 30 nm Au NPs were obtained by a slightly modified Turkevich and Frens method using sodium citrate as both reducing and stabilizing agent at high temperature. The attempt to produce Au NPs with diameter larger than 30-40 nm by the Turkevich method resulted in an increase in the polydispersity and the shape diversity of the final Au NPs, indicating the importance of the trial of new reducing agents in the production of Au NPs especially for diameters above 40 nm. Therefore, hydroxylamine-o-sulfonic acid (NH2SO4H) (HOS) was used here for the first time as a new reducing agent for HAuCl4 at room temperature to produce Au NPs with diameter of about 60, 90 and 150 nm. This new method using HOS is an extension of the approaches described to produce Au NPs with diameter above 40 nm by direct reduction. The obtained nanoparticles were characterized using uv-visible spectroscopy, dynamic light scattering (DLS) and transmission electron microscopy (TEM). Further biocojuguation on 15, 30 and 90 nm Au NPs were performed by grafting covalently Apolipoprotein E (ApoE) and Bovine Serum Albumin (BSA) through an ethylene glycol-N-hydroxysuccinimide linker (NHS-PEG-S-S-PEG-NHS) making them very attractive for drug delivery and cell targeting. Finally, functionalized polyethylene glycol-based thiol polymers were also used to stabilize the pre-synthesized Au NPs-PEG-Protein.