A facile route of gold nanoparticle synthesis and surface modification using amino-terminated poly(ethylene oxide)-poly(propylene oxide) block copolymers.

We report here a facile synthetic method and surface modification of gold nanoparticles using amino-terminated poly(ethylene oxide)-poly(propylene oxide) block copolymers (CH3-[OCH2CH2]x-[OCH2CH(CH3)]y-NH2; EO(x)PO(y)NH2) (SURFONAMINE) as media, reducing agents, stabilizing agents and surface-modifying agents. Gold nanoparticles were synthesized through autoreduction of hydrogen tetrachloroaureate(III) hydrate (HAuCl4 x 3H2O) by SURFONAMINE as media and reducing agents at ambient conditions (approximately 25 degrees C). The AuCl4- reduction and gold nanoparticle formation were promoted by SURFONAMINE with longer PEO segment and heating. The enhanced-activity of SURFONAMINE for AuCl4- reduction contributed to particle growth due to the AuCl4- reduction by SURFONAMINE anchored on gold nanoparticles. Furthermore, amphiphilic property of the gold nanoparticle surface was controlled in terms of EO/PO unit ratio of SURFONAMINE. For example, gold nanoparticles synthesized in SURFONAMINE L-207 (EO33PO10NH2) homogeneously mixed with water but not with cyclohexane. On the other hand, gold nanoparticles synthesized in SURFONAMINE B-200 (EO6PO29NH2) were miscible with cylcohexane while immiscible with water.