The synthesis of ultrafine gold nanoparticles in presence of maltose modified hyperbranched poly(ethyleneimines) (PEI) is described. The polymer acted as both a reducing and stabilising agent in the particle formation process. The nanoparticles were characterized by means of dynamic light scattering (DLS), transmission electron microscopy (TEM), analytical ultracentri fugation (AUC), small angle x ray scattering (SAXS), and small angle neutron scattering (SANS). The mechanism of nanoparticle formation can be described in two steps. The reduction process of the Au 3þ ions located in the inner coil region of the hyperbranched PEI led to the for mation of a compact gold core, and is accompanied by a collapse of the polymer coil. Therefore, in the subsequent reduction process a gold polymer hybrid shell is formed. By using the PEI of higher molar mass, core shell gold nanoparticles of about 3.6 nm size with a more narrow size distribution and special fluorescence behavior could be synthesized. Keywords Gold nanoparticles, gold polymer hybrid shell, maltose modified poly (ethyleneimine) The authors thank Antje Vö lkel (MPI KGF) for the skilfully performed analytical ultracentrifugation experiments. Addition ally, they like to thank C. Oppel and S. Prévost for help with the SAXS and SANS experiments, respectively. Sibylle Rü stig is gratefully acknowledged for the TEM micrographs.
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