PREPARATION OF FUNCTIONAL SILANE-STABILIZED GOLD COLLOIDS IN THE (SUB)NANOMETER SIZE RANGE

A synthesis method is introduced for very small uniform gold particles (diameter less than 5 nm), based on the reduction of hydrogen tetrach loroaurate(III) in ethanol in the presence of (gamma-mercaptopropyl)tr imethoxysilane (MPS). The surface layer of MPS molecules gives the gol d particles a high colloidal stability and allows in principle further reaction with any silane coupling agent. Decrease of the HAuCl4: MPS ratio allows a controlled reduction of gold particle size, resulting i n remarkably uniform gold dusters of (sub)nanometer size, observed wit h high-angle-annular-dark-field scanning transmission electron microsc opy. After attachment of (gamma-aminopropyl)triethoxysilane (APS) to t he MPS surface layer, other molecules may be covalently bound to the g old colloid via the amine group of APS. As an illustrative example we prepared in this manner gold particles labeled with a fluorescent dye. The chemical structure of the surface silanes was studied with Fourie r transform infrared spectroscopy.