Synthesis of CdSe/CdS core/shell quantum dots for biological sensing applications

A simple, room temperature, one-pot method to produce biocompatible CdSe/CdS quantum dots (QDs) in aqueous solution is presented. CdCl2 and NaSeSO3 are the precursors for the CdSe core where gelatin is used as an inhibitor. A CdS shell is grown by injecting H2S gas, generated by a reaction between sulfuric and sodium sulfide, into the solution. This fast, low cost synthesis approach is simple for scale-up production of QDs. Transmission electron microscopy shows that the bare CdSe quantum dots were 2-3 nm in diameter. The emission peak from the CdSe can be tuned over most of the visible wavelength (from 520nm to 600 nm) as the diameter of the QDs is allowed to increase before growth of the CdS shell. The core/shell structure was confirmed via UV-Vis absorption spectroscopy, PL studies, and structural characterization (XRD). The higher band gap CdS coatings significantly enhanced the photoluminescence (PL) of CdSe quantum dots by a factor of 2-3. However, the large lattice mismatch between the CdS coating and the CdSe core results in eventually quenched luminescence from CdSe with thicker CdS coatings. To increase the photochemical stability and biocompatibility of the CdSe/CdS QDs, a silica coating is grown directly on the QDs. Preliminary data indicates that the PL from CdSe/CdS QDs post-growth is affected as the applied electric field is altered. Efforts to functionalize the QDs with DNA and antibodies have begun. Studies have been initiated to demonstrate the feasibility of microinjecting the QDs into Xenopus embryo with minimal post-synthesis processing.