Spectroscopic investigations of CdTe quantum dot stability in different aqueous media

For the successful use of quantum dots (QDs) in biomedicine their chemical and optical stability is of great importance. In this study the changes of photoluminescence parameters of CdTe QDs coated with mercaptopropionic acid (MPA) dependently on time and environment are presented. The presence of salt ions in the QD water solution decreases photoluminescence band intensity and induces red shift. The pH value of the solution also influences spectroscopic properties of QDs. In the pH range from 2.5 to 9 a decrease of photoluminescence intensity is observed. The fastest one, leading to the complete luminescence bleaching, occurs in the most acidic medium. Changes of QD spectral properties in cell growth media were studied as well. The results imply that spectroscopic changes of CdTe-MPA QDs are caused by the interactions between the ions present in the solution and ligand coating of QDs. The model of possible processes is proposed.