Highly selective recognition of naphthol isomers based on the fluorescence dye-incorporated SH-β-cyclodextrin functionalized gold nanoparticles

In present work, a rhodamine 6G (Rh 6G)-incorporated beta-cyclodextrin functionalized gold nanoparticle (Rh 6G-CD-AuNP) based fluorescent assay has been successfully developed for recognizing/detecting the structural isomers, alpha-naphthol and beta-naphthol, in aqueous solution. The beta-cyclodextrin functionalized gold nanoparticles (CD-AuNPs) are achieved by conjugating the thiolated beta-cyclodextrin (SH-beta-CD) with AuNPs via S-Au covalent bonds. Rhodamine 6G (Rh 6G) is chosen as a fluorescent probe in this approach because it can be strongly absorbed on the surface of AuNP by noncovalent interaction. After binding with beta-CD cavity, the naphthols enable to act as electron transfer quenchers of Rh 6G, which lead to significant fluorescence quenching of the dye. Because of different association ability of naphthol isomers with the beta-CD cavity, the assay can selectively distinguish alpha-naphthol and beta-naphthol with reasonable sensitivity. Detection of naphthols down to 8 nM with a dynamic range of nearly three orders of magnitude (0.01-8 mu M) for alpha-naphthol and 50 nM with two orders of magnitude (0.1-20 mu M) for beta-naphthol is demonstrated, respectively. The ability of the method for detecting the content of alpha-naphthol or beta-naphthol in the different naphthol mixtures has also been evaluated. (C) 2010 Elsevier B.V. All rights reserved.