Fabrication of gold-calcium phosphate composite nanoparticles through coprecipitation mediated by amino-terminated polyethylene glycol.

Calcium phosphate (CaP) nanoparticles immobilizing gold (Au) nanocrystals (Au-CaP composite nanoparticles) would be useful in diagnoses and/or treatments with Au nanocrystals. In this study, we achieved the rapid one-pot fabrication of such nanoparticles via coprecipitation in labile supersaturated CaP solutions by using appropriate Au sources, namely, Au nanocrystals coated with amino-terminated polyethylene glycol (PEG). In this process, amino groups at the PEG terminal played a crucial role in the coprecipitation with CaP through affinity interactions, and thus in the formation of Au-CaP composite nanoparticles; however, the molecular weight of the PEG chain was not a controlling factor in the coprecipitation. The important role of the functional groups at the PEG terminal was suggested by comparison with Au nanocrystals coated with carboxyl- and methoxy-terminated PEG, both of which barely coprecipitated with CaP and failed to form Au-CaP composite nanoparticles. Au nanocrystals coated with amino-terminated PEG were immobilized on the CaP nanoparticles, thereby regulating their size (∼140 nm in hydrodynamic diameter) and their dispersion in water. This coprecipitation process and the resulting Au-CaP composite nanoparticles have great potential in biomedical applications.