Gold nanorods (GNRs) with SiO2 overcoatings are of interest for enhancing the stability of GNRs during photothermal heating, for allowing functionalization with silanes, and for some specific applications, such as ultrasound imaging.  While methods have recently been developed for synthesizing GNRs on a large scale, SiO2 overcoating reactions are still limited to small reaction scales.  Here, we report a method for large-scale overcoatings, which gives ~200 mg of SiO2-overcoated GNRs (SiO2-GNRs).  SiO2 overcoatings are deposited onto and encapsulate the cetyltrimethylammonium bromide (CTAB) bilayers that stabilize GNRs by continuously adding tetraethoxysilane (TEOS) via syringe pump.  Continuous addition is important for keeping the TEOS concentration sufficiently low to allow for uniform overcoatings on individual GNRs.  Optical absorbance spectra of SiO2-GNRs closely resemble uncoated GNRs, which indicates overcoating of single (rather than multiple) GNRs and confirms that they remain well dispersed.  The SiO2 shell thickness can be controlled by adjusting the reaction conditions, giving shells as thick as 30 nm.  For thin (< 10 nm) coatings, addition of a poly(ethylene oxide) silane (PEG-silane) during growth allows for facile control over the shell thickness, giving overcoatings as thin as 3 nm.  The bulky PEG chain terminates further crosslinking and deposition of SiO2; timing of addition of PEG-silane allows for control of the SiO2 shell thickness.

Large-scale silica overcoating of gold nanorods with tunable shell thicknesses

248th National Meeting (2014)

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