Multifunctional conjugates to prepare nucleolar-targeting CdS quantum dots.

We used a click reaction to synthesize a bidentate 1,2,3-triazole-based ligand, TA, for use in the preparation of aqueous CdS quantum dots (QDs). TA-conjugated CdS QDs exhibited two fluorescence emission peaks, one at 540 nm arising from CdS nanocrystals and the other at approximately 670 nm arising from TA-CdS QD complexes formed via surface coordination. Coordination between TA and CdS was verified by using X-ray photoelectron (N 1s) spectra as well as Raman and NMR spectra of TA-capped QDs. Electrochemical analysis revealed that the 1,2,3-triazole moities in TA form complexes with the Cd(II) ions. The aqueous QDs protected by TA were very stable at different ionic strengths and over a broad pH range, according to fluorescence analysis. The ethidium bromide exclusion assay demonstrated that the bidentate TA ligand interacts strongly with DNA. Fluorescent micrographs and TEM images of cancer cells stained with TA-capped QDs clearly showed that the TA ligand targeted CdS QDs to the nucleoli of cells. In contrast, thioglycolic acid-capped CdS QDs just stained the cell membranes and could not pass the cell membranes to reach the cell nucleus.