Understanding and controlling gold nanoparticle formation from a robust self-assembled cyclodextrin solid template

Recently, we discovered that cyclodextrin (CD)-stabilized gold nanoparticles could be synthesized in an aqueous medium from a self-assembled supramolecular structure of CD and gold salt. We showed that the self-assembled structure of the CD complex induced by the gold salt acted as a solid template for the formation of nanoconfined gold seeds and that gold seeds grew into CD-stabilized gold nanoparticles in water without the necessity of other reducing or stabilizing agents. Here, we extensively investigate the supramolecular self-assembled structure of the CD/gold salt complex under various synthetic conditions, the mechanism of the α-CD-stabilized gold nanoparticles formation, and the processing parameters for controlling the size of gold nanoparticles. We demonstrate that gold salts were confined between two different crystalline phases of the supramolecular CD solid template via a gold salt-induced molecular self-assembly process and that thermal treatment of the CD/gold salt complex led to the formation of nanosized gold seeds geometrically confined within the crystalline interface region. Placement of the thermally treated complex in water without the addition of any supplementary additives proliferated the growth of CD-stabilized gold nanoparticles via stabilization of the growing gold seed intermediates by CD molecules. In addition, various processing parameters such as Au salt concentration are shown to affect the size of AuNPs.