(637j) Rapid Synthesis of Polymer-Stabilized Metal Colloids

We present rapid, room temperature synthesis of PEG-stabilized gold nanoparticles using Flash NanoPrecipitation (FNP), a polymer directed self-assembly method.  During FNP, an aqueous solution of gold chloride is rapidly mixed with an amphiphilic PEG-based block copolymer dissolved in an organic solvent with a reducing agent, tannic acid (TA).   Upon mixing, gold chloride is reduced by TA and encapsulated by the self-assembling PEG-based block copolymer.  Simultaneous gold reduction and polymer self-assembly facilitated by the rapid mixing prevent secondary nucleation and Ostwald ripening.  The result is kinetically controlled growth and size focusing of encapsulated gold nanoparticles of uniform size (standard deviation <15%).  The size of the resulting gold nanoparticles and hydrodynamic diameter of the nanoparticle construct can be tuned by varying the pH.   We anticipate FNP will be a versatile platform for single-step, room temperature processing PEG-stabilized gold nanoparticles with tunable surface chemistry.  Continuous processing may also be possible.