Interaction of β-cyclodextrin-capped CdSe quantum dots with inorganic anions and cations

A facile method was developed for the preparation of water soluble beta-Cyclodextrin (beta-CD)-modified CdSe quantum dots (QDs) (beta-CD-QDs) by directly replacing the oleic acid ligands on the QDs surface with beta-CD in an alkaline aqueous solution. The as-prepared QDs show good stability in aqueous solution for several months. Oxoanions, including phosphoric acid ion, sulphite acid ion and carbonic acid ion, affect the fluorescence of beta-CD-QDs. Among them, H2PO4- exhibited the largest quenching effect. For the polyprotic acids (HO)(3)AO, the effect of acidic anions on the fluorescence of beta-CD-QDs was in the order: monoanion (HO)(2)AO(2)(-) > dianion (HO)AO(3)(2-) >> trianion AO(4)(3-). After photoactivation for several days in the presence of anions at alkaline pH, the beta-CD-QDs exhibited strong fluorescence emission. The effect of various heavy and transition metal ions on the fluorescence properties of the beta-CD-QDs was investigated further. It was found that Ag+, Hg2+ and Co2+ have significant quenching effect on the fluorescence of the beta-CD-QDs. The SternVolmer quenching constants increased in the order: Hg2+ < Co2+