Direct Synthesis of Aqueous CdSe/ZnS-Based Quantum Dots Using Microwave Irradiation

This study focuses on an aqueous one-pot method for synthesis of CdSe/ZnS core/shell QDs using microwave radiation. The novelty of the study is the use of Zn(NH3)4 as the zinc source. Using an initial solution with the composition Cd1Se1Zn6MPA20, the QDs obtained upon heating at 160 °C for 60 min were not high quality, as evidenced by a quantum yield of 1.5%, due to the poor interface between the core and shell. Postsynthesis UV irradiation of the as-prepared QDs for 30 min could be used to improve the quantum yield to 22%, but the technique is not practical for large-scale applications. By increasing the amount of Cd2+ in the initial solution to Cd4Se1Zn4MPA20, we formed CdSe/CdS/ZnS QDs after heating at 150 °C for 90 min, which contained less interfacial trap-states and as a result, had a higher quantum yield of 13%. These QDs were characterized by powder diffraction, electron microscopy, and X-ray photoelectron spectroscopy. Uptake of the microwave-optimized QDs by alveolar macrophages was compared in a side-by-side study against commercial QDs, QDot585. Despite having a lower relative quantum yield (13%) as compared to the commercial QDs (65%), the microwave-synthesized QDs at 20 nM concentrations were readily detected within the macrophages after 20 min of incubation.