Stable water-soluble CdSe/ZnS quantum dots with higher quantum efficiency as fluorescent biological label

Oil-soluble CdSe/ZnS (CdSe core, ZnS shell) semiconductor quantum dots (QDs) have been prepared in a non-coordinating solvent and successfully turned into a water phase with a quantum efficiency as high as 48 per cent by using mercaptopropionic acid (MPA). MPA watersoluble QDs have the same optical spectra compared with those formed initially in organic solutions. The fluorescence intensity of the water-soluble QDswould last for several months in air. Bovine serum albumen (BSA) has been grafted onto the water-soluble QDs with covalent bonds by way of the chemical reaction of QDs with N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS) to form the BSA-QDs. Electrophoresis of the BSA-QDs with 1 per cent agarose has been performed in the buffer solution of phosphate buffer (PB, pH = 7.4) to check the bioconjugation of QDs and BSA. Similarly, the QDs have been used as the fluorescent biological probe to label the antibody conjugated to the hepatitis B surface antigen (anti-HBs) and the corresponding positive control. The fluorescence microscope photographs prove that the anti-HBs and the corresponding positive control have not lost their biological activity. The results indicate that the water-soluble QDs can be very effective in cellular imaging.