Synthesis of dendrimer-passivated noble metal nanoparticles in a polar medium: Comparison of size between silver and gold particles

The synthesis of silver and gold metal nanospherical particles stabilized b y the fourth-generation poly(amido amine) (G4 PAMAM) dendrimer is reported. The reduction of silver nitrate and sodium tetrachtoroaurate in the presen ce of the PAMAM dendrimer having terminal amine groups results in the forma tion of stable, water-soluble nanoparticles. The formation and size of the particles have been determined fi om the UV-vis plasmon absorption band and transmission electron microscopic (TEM) analyses. The average particle siz es are (6.2 +/- 1.7)-(12.2 +/- 2.9) nm for silver and are (3.2 +/- 0.7)-(7. 3 +/- 1.5) nm for gold, depending on the metal ion-to-dendrimer terminal am ine ratio (M:D) used. Thus, dendrimer-protected silver particles are substa ntially larger than the gold particles synthesized in similar systems. Nano particles prepared at 0.25:1 and lower M:D ratios are stable for a long per iod of time. A TEM study of the morphology also shows a short-ranged hexago nal arrangement of particles in a monolayer onto the carbon-coated copper T EM grid. Detailed particle size analysis studies by TEM support the possibi lity that the terminal amino groups of the dendrimers take part in the stab ilization of the nanoparticles. The evidence from X-ray photoelectron spect roscopic and Fourier transform infrared absorption spectroscopic investigat ions confirms the valence state of the gold and the encapsulation by the de ndrimer.