(354e) Polymer-Induced Single-Step Synthesis And Stabilization Of Noble Metal Nanoparticles In Water

Metal nanoparticles, particularly gold, have received wide attention because of the unique optical properties of these particles for applications in photonics, detection systems, device fabrication, and catalysis. For this reason, different synthetic methods have been developed to generate monodisperse gold nanoparticles (AuNPs) either in aqueous or organic media. One of the most widely-used methods is the reduction of tetrachloroaurate ions (AuCl4-) in aqueous medium using sodium citrate.1 However, this method lacks good control over the synthesized particle size and the size dispersion is rather poor. The Brust method and various modifications are useful for the generation of AuNPs having core sizes ranging from 1 to 4 nm.2 In the Brust method, the transfer of AuCl4- into toluene or chloroform is performed using tetraalkylammonium bromide followed by reduction with sodium borohydride in the presence of alkylthiols. In addition to all of the above-mentioned methods, reduction of gold salt to AuNPs by amine-containing organic molecules also has been investigated and successfully accomplished.3 However, most of the amine compounds used in the AuNP synthesis are only soluble in organic solvents. As a result the reduction reaction must be performed in organic solvents, or in a biphasic system. Consequently, the applications of nanoparticles in biological system are unfavorable because the biomolecules are unstable in organic medium. We report a simple, inexpensive, single-step synthesis of gold and silver nanoparticles using poly(allylamine) (PAAm) as a reducing and stabilizing agent. The synthesis was carried out in aqueous solution, making the method versatile and environmentally friendly. The synthesized polymer-stabilized nanoparticles showed exceptional stability in water for months. The polymer-stabilized gold nanoparticles were allowed to undergo ligand exchange with a variety of ω-functionalized alkylthiols including acid-, alcohol-, amine-, and biotin-terminated thiols. The methodology also is applicable for the generation of silver nanoparticles.

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