Microwave-assist Aqueous Synthesis, Optical Properties And Bioapplication Of CdSeTeS Quaternary Alloyed QDS

Quantum dots (QDs), also referred to semiconductor nanocrystals, have been successfully used in biological and biomedical fields such as bio-tagging and bio-imaging because of their unique optical properties, such as narrow emission spectra, continuous absorption band, size-dependent emission wavelength and great photostability. Compared to traditional binary QDs like CdTe, CdSe, ZnSe and so on, ternary or quaternary alloyed QDs have attracted significant attention recent years due to their composition-dependent optical properties besides size-dependent optical properties. At present, certain ternary alloyed QDs have been successfully synthesized in water phase and organic phase, but there are few reports about the synthesis of quaternary alloyed QDs. To the best of our knowledge, we have not found any quaternary alloyed QDs that consist of a common cation and three different kinds of anions. We guess that these new quaternary alloyed QDs probably have some special optical properties. In this paper, CdSeTeS quaternary alloyed QDs were for the first time synthesized in water by microwave irradiation using mercaptopropionic acid (MPA) as the stabilizer and the source of sulfur. Furthermore, the optical properties of CdSeTeS QDs were investigated systematically. Finally, the CdSeTeS QDs were successfully applied to targeted imaging for SiHa cancer cells as fluorescent probes. The main contributions are as follows:Firstly, the precursor solutions were prepared with CdCl₂·2.5H₂O,NaHX (X=Se, Te) and MPA. CdSeTeS quaternary alloyed QDs were synthesized in water by microwave irradiation. The influences of certain factors, such as the heating time, the Se:Te ratio, the MPA ratio, the concentration of precursor solutions and the reaction temperature, on the synthesis of CdSeTeS QDs were investigated. In the optimal conditions, a series of quaternary alloyed QDs with different emission wavelengths, exhibiting photoluminescence from 549 to 709 nm, were prepared. The experimental results of high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX) and powder X-ray diffraction (XRD) indicated that the as-prepared nanocrystals possessed quaternary alloy structure with high crystallinity. The characterization of UV absorption spectroscopy and fluorescence spectroscopy demonstrated that CdSeTeS quaternary alloyed QDs exhibited good water solubility, chemical stability and high QY (up to 57.7 %). Meanwhile, the results also revealed that microwave irradiation was a convenient and efficient approach for the synthesis of alloyed QDs.Secondly, the optical properties of CdSeTeS QDs were investigated systematically by using UV absorption spectroscopy, fluorescence spectroscopy, steady/transient state fluorescence spectroscopy and fluorescence correlation spectroscopy (FCS). Our results illustrated CdSeTeS QDs had size-dependent and composition-dependent optical properties. Most importantly, the quaternary alloyed QDs possessed very long fluorescence lifetime (more than 100 ns) and excellent photostability.Finally, the CdSe_0.2Te_0.8S QDs with the fluorescence emission peak at 652 nm were chose to conjugate with the epidermal growth factor receptor (EGFR) monoclonal antibody (Erbitux) as fluorescent probes. The conjugates were characterized by FCS. Furthermore, QDs- Erbitux as labeling probes were successfully applied to targeted imaging of SiHa cervical cancer cells. Compared with the control sample, the strong contrast effect can be observed. We believe that CdSeTeS QDs will become a very useful probe in vivo targeted imaging and clinical diagnosis.