Functional core/shell nanoparticles via layer-by-layer assembly. investigation of the experimental parameters for controlling particle aggregation and for enhancing dispersion stability

Gold nanoparticles (AuNPs) with a size of 13.5 nm were synthesized using well-established methods as described earlier by Turkevich (Turkevich, J.; Stevenson, P. C.; Hillier, J. Discuss. Faraday Soc. 1961, 11, 55-75) and Frens (Hens, G. Nature (London), Phys. Sci. 1973, 241, 20-22) using citrate as the reducing agent. It has already been, reported that such AuNPs can easily be coated with polymeric shells using electrostatic layer-by-layer assembly of certain polyelectrolytes. Here, we show which parameters, namely, the polyelectrolyte concentration, the contour length of the polyelectrolyte chain, and the ionic strength, are preventing bridging flocculation during polyelectrolyte adsorption and enhancing the stability of the colloidal dispersion. For the preparation of individually coated particles with high yield, we identified optimal conditions such as the degree of polymerization of the polyelectrolytes used, the polyelectrolyte concentration, the nanoparticle concentration, and the concentration of added NaCl during multilayer buildup. Surprisingly, such functional nanoparticles are obtained with highest yield at a moderate excess of polyions. In contrast to expectations, a larger excess of polyions leads again to slight destabilization of the dispersion. The present findings raise our confidence to establish layer-by-layer deposition as a general method for functionalizing even different nanoparticles using a single method.