Preparation of bioconjugates of CdTe nanocrystals for cancer marker detection

Highly fluorescent CdTe quantum dots (Q-dots) stabilized by 3-mercaptopropionic acid (MPA) were prepared by an aqueous solution approach and used as fluorescent labels in detecting a cancer marker, carcinoembryonic antigen (CEA), expressed on human colon carcinoma cell line LS 180. Nonspecific adsorptions of CdTe Q-dots on carcinoma cells were observed and effectively eliminated by replacing MPA with a thiolated PEG ( poly( ethylene glycol), Mn = 750) synthesized according to literature. It was unexpectedly found out that the PEG- coated CdTe Q-dots exhibited very strong and specific affinity to anti-CEA monoclonal antibody rch 24 ( rch 24 mAb). The resultant CdTe -(rch 24 mAb) conjugates were successfully used in detections of CEA expressed on the surface of cell line LS 180. Further experiments demonstrated that the fluorescent CdTe Q-dots exhibited much better photostability and a brighter fluorescence than FITC, which consequently led to a higher efficiency in the cancer marker detection.