Luminescent CdTe/CdS core-shell and CdTe/CdS/ZnS multi-layer quantum dots: synthesis and investigations for bioapplication

摘要

Concerns on quantum dots (QDs) have been continuously increasing because of their advantages on photophysical properties. Water soluble CdTe/CdS core-shell and CdTe/CdS/ZnS multi-layer QDs were synthysized with mercaptopropanoic acid (MPA) as stabilizer in aqueous phase in the current research. The obtained QDs were characterized with fluorescence spectrum (FS), and quantum yields (QYs) was calculated base on the resulting data from FS. Comparing with CdTe core, red-shift of maximum emission wavelength (MEW) of CdTe/CdS was observed, which indicated the growth of QDs size. To obtain high QYs of CdTe/CdS core-shell QDs, several methods and different reaction conditions were investigated and discussed, such as dependence of Cd~(2+) concentration, dependence of pH, influence of S~(2-):Te~(2-), and effect of Cd~(2+):S~(2-) etc. Among all of discussed methods, QYs of core-shell CdTe/CdS is generally degressive with refluxing time elapsing. The best QYs of 79.8% can be achieved when pH was set at 8.5, Cd~(2+):S~(2-) = 1:0.1 (mol ratio). Moreover, CdTe/CdS/ZnS multi-layer QDs was prepared, and results via FS indicated a further red-shift from 554 nm to 646 nm comparing with CdTe/CdS QDs, but QYs decreased to 14.0%. QDs currently discussed in this research are easily synthesized, and safe to organism, i.e. biocompatible. They will be useful in applications of biolabeling, imaging, and biosensing based on fluorescence resonance energy transfer (FRET).