Preparation and Characterization of 1-2 nm DendrimerEncapsulated Gold Nanoparticles Having Very Narrow Size Distributions

Highly monodisperse, 1-2-nm diameter Au nanoparticles were prepared using poly(amidoamine) (PAMAM) dendrimers as templates. The synthesis is carried out in water, takes less than 30 min, and requires no subsequent purification. Au nanoparticles having diameters of 1.3 (plus_minus) 0.3 and 1.6 (plus_minus) 0.3 nm were obtained when 55 and 140 equiv, respectively, of HAuCl4 per dendrimer were used. For unpurified Au nanoparticles in this size range, this represents more than a 200% improvement in size distribution compared to previous reports. The high monodispersity is a function of the template synthesis, which avoids size variations arising from random nucleation and growth phenomena, and the use of magic number equivalent ratios of AuCl4-\dendrimer. When a nonmagic number of AuCl4equivalents per dendrimer was used, a significantly more polydisperse distribution of Au nanoparticles was obtained.