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 water-soluble QDs have the same optical spectra compared with those formed initially in organic solutions. The fluorescence intensity of the water-soluble QDs would 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, =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.