Highly controlled core/shell structures: Tunable conductive polymer shells on gold nanoparticles and nanochains

Controls in coating gold nanoparticles with conductive polymers are reported, where uniform core/shell nanoparticles with tailored core aggregation and shell thickness are unambiguously demonstrated. In the presence of sodium dodecylsulfate (SDS), the adsorption and in situ polymerization of aniline or pyrrole on the surface of gold nanoparticles gives uniform polymer shells. A typical single encapsulation of 10 nm gold nanoparticles gave ∼99.1% monomers out of 1074 particles surveyed. The shell growth was found to be kinetically controlled; polyaniline was successively grown on 22 nm gold nanoparticles by multiple growth cycles, giving shell thicknesses of 14, 31, 61 and 92 nm, respectively. We show that the aggregation of gold nanoparticles can be controllably promoted in this system, by simply timing SDS addition, to give linearly aggregated cores of 2-20 particles. The in situ formation of conductive polymer shells has allowed the isolation and unambiguous characterization of these nanochains for the first time. The one-step, "mix-and-wait" synthesis solely utilizes inexpensive starting materials and is, therefore, well-suited for fabrication of large quantities of core/shell nanoparticles. The core/shell nanoparticles form stable colloidal suspensions and can be readily purified by centrifugation.