Gas-phase synthesis of multicomponet magnetic/plasmonic nanoparticles for cancer theranostics

Abstract

Multi-component nanoparticles have promise for cancer theranostics. This research developed a gas-phase approach for synthesis of multi-layer magnetic/plasmonic nanoparticles, consisting of a superparamagnetic iron oxide core, a continuous silica shell, and an outer layer decorated with gold nanoparticles. These multi-layer nanoparticles can be further coated with hydrophilic polyethylene glycol (PEG), and dispersed in a water solution for future testing, such as imaging, heating, and targeted delivery. Key challenges for manufacturing such nanoparticles include control of the dimensions, morphology, chemical composition and functional properties of each layer. Superparamagnetic iron oxide nanoparticles (SPIONs) were produced in a DC thermal plasma using ferrocene as the iron precursor. Particle composition and magnetic properties were affected by the O₂ flow rate, plasma power, location of the ceramic tube positioned above the nozzle exit, and use of dilution argon injected downstream of the ferrocene packed bed. The achieved optimum product had a saturation magnetization equalling ~40 emu/g with a coercivity of 26 Oe and a remanence of 1.5 emu/g. These particles had a mean diameter ~9 nm, and mainly contained the magnetite phase. These results were the best ever reported for synthesis of SPIONs by a plasma process. Plasma-synthesized SPIONs were transported into a coating chamber where a continuous silica shell was grown by means of photo-induced chemical vapor deposition. Silica coating thickness could be tuned between sub-nanometer to several nanometers by varying the residence time and silica precursor flow rate. Gold decoration was achieved by passing silica-coated iron oxide nanoparticles through a gold hot-wire generator and decoration chamber where small gold nanoparticles were scavenged on the silica surface. A two-step, gas-phase process was developed for PEGylating gold-decorated silica nanoparticles, by modifying the gold surface with hydroxyl groups, followed by inserting ethylene oxide vapor for polymerization. PEG thickness depended on the ethylene oxide flow rate, PEGylation temperature, and density of the hydroxyl groups on the particle surface. This work was the first reported gas-phase PEGylation of gold-decorated silica nanoparticles. Several online methods, including scanning mobility particle sizing and tandem differential mobility analysis, were used for characterization of particle size distribution and thickness of individual layers. Particle morphology was characterized by transmission electron microscopy (TEM) with particles collected onto TEM grids, and elemental composition are characterized by energy dispersive spectroscopy in scanning TEM. Bulk powder samples were collected on filters for offline characterization by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and magnetic property measurement instruments.