Sonochemical Synthesis of Cyclodextrin-Coated Quantum Dots for Optical Detection of Pollutant Phenols in Water

A simple, rapid sonochemical procedure for the preparation of highly fluorescent and water-soluble CdSe/ZnS quantum dots (QDs) using (alpha-. beta-, and gamma-cyclodextrin (CD) as surface-coating agents is reported. The water-soluble QDs were characterized by luminescence spectroscopy, UV-vis spectroscopy., Fr-IR spectroscopy. NMR spectroscopy, and transmission electron microscopy (TEM). The quantum yields (QYs) of alpha-CD-QDs, beta-CD-QDs, and gamma-CD-QDs in water were about 45, 39. and 27%. respectively. The n-CD-QDs allow highly sensitive determination of phenols by changing CD coating via fluorescence illtenSity quenching. The a-CD-QDs and P-CD-QDs are sensitive toward p-nitrophenol and I -naphthol, respectively. Under optimal conditions, the relative fluorescence intensities of alpha-CD/CdSe/ZnS QDs and beta-CD/CdSc/ZnS QDs both decreased linearly with increasing p-nitrophenol and 1-naphthol in the concentration ran-e of 0.01-100 mu M, with the corresponding detection limits (3(7) of 7.92 x 10(-9) and 4.83 x 10(-9) M. respectively. However, the sensitivity of n-CD-QDs toward other phenols, including o-nitrophenol, m-nitrophenol, 2-naphthol, o-cresol, m-cresol and p-cresol, are negligible. It is found that p-nitrophenol and 1-naphthol call quench the luminescence of alpha-CD-QDs and beta-CD-QDs in a concentration-dependent manner that is best described by a Stern-Volmer-type equation. The possible underlying mechanism is discussed.