Facile Solvothermal Preparation of Monodisperse Gold Nanoparticles and Their Engineered Assembly of Ferritin–Gold Nanoclusters

Herein, we report a quick and simple synthesis of water-soluble gold nanoparticles using a HAuCl4 and oleylamine mixture. Oleylamine serves as a reduction agent as well as a stabilizer for nanoparticle surfaces. The particle sizes can be adjusted by modulating reaction temperature and time. Solvothermal reduction of HAuCl4 with oleylamine can be confirmed by measuring the product in Fourier transform infrared (FTIR) spectroscopy. The plasmon band shifting from yellow to red confirms a nanosized particle formation. Amide bonds on the surface of the nanoparticles formed hydrogen bonds with one another, resulting in a hydrophobic monolayer. Particles dispersed well in nonpolar organic solvents, such as in hexane or toluene, by brief sonication. Next, we demonstrated the transfer of gold nanoparticles into water by lipid capsulation using 1-myristoyl-2-hydroxy-sn-glycero-3-phosphocholine (MHPC), 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-(methoxy polyethylene glycol)-2000 (DPPE-PEG2k), and 1,2-dioleoyl-sn-glycero-3-N-{5-amino-1-carboxypentyl}iminodiacetic acid succinyl nickel salt [DGS-NTA(Ni)]. The particle concentration can be obtained using an absorbance in ultraviolet–visible (UV–vis) spectra (at 420 nm). Instrumental analyses using transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) analysis, dynamic light scattering (DLS), and FTIR confirmed successful production of gold nanoparticles and fair solubility in water. Prepared gold particles were selectively clustered via engineered ferritin nanocages that provide multiple conjugation moieties. A total of 5–6 gold nanoparticles were clustered on a single ferritin nanocage confirmed in TEM. Reported solvothermal synthesis and preparation of gold nanoclusters may serve as an efficient, alternate way of preparing water-soluble gold nanoparticles, which can be used in a wide variety of biomedical applications.