Glutathione (GSH)-capped CdTe quantum dots (GSH-CdTe QDs) were synthesized in aqueous solution. In pH 7.4 Tris-HCl buffer medium, acridine orange (AO) was adsorbed to the surfaces of GSH-CdTe QDs via electrostatic attraction and formed ground state complex, which resulted in the quenching of the fluorescence of GSH-CdTe QDs. Adding ctDNA to GSH-CdTe QDs-AO system leaded to the fluorescence intensity of GSH-CdTe QDs recover, which can be explained by that the addition of ctDNA to the system induced AO to dissociate from the surface of GSH-CdTe QDs and embed into its double helix structure. According to the fluorescence quencher and restoration for GSH-CdTe QDs, fluorescence reversible control of QDs was realized. The fluorescence intensity change of GSH-CdTe QDs-AO system aroused by the addition of ctDNA was proportional to the ctDNA concentration in a certain range, and its detection limit was 0.13 ng•mL^－1. Based on it, the simple, rapid, accurate and sensitive methods had been proposed to determine ctDNA. The interaction of GSH-CdTe QDs-AO-ctDNA was studied by resonance Rayleigh scattering (RRS), absorption spectra and image of atomic force microscopy. The interaction mechanism was discussed and corresponding model of interaction was built.

Key words: CdTe quantum dot, acridine orange, calf thymus DNA, fluorescence reversible control