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Nanobiosensors for Health Monitoring

Final Report Summary - NANHEMO (Nanobiosensors for Health Monitoring)

The main goal of this research is the synthesis of water soluble core-shell CdSe/ZnS quantum dots (QDs) and their suitability in biosensing using an electrochemiluminescence-based detection method.
Water soluble QDs have been synthesized using the ligand exchange method. We synthesized dimethylaminoethanethiol (DAET)-capped CdSe/ZnS QDs from CdSe/ZnS Lumidots® in toluene. DAET/CdSe/Zns QDs showed an emission peak (see Fig. 1) maximum at 670 nm which corresponds to a particle size of 6.3 nm (dark red emission). DAET ligand is used as a surfactant which renders the CdSe/ZnS QDs water soluble. The ligand on the surface of a quantum dot prevents aggregation of individual particles. A ligand exchange phase transfer method allowed changing the original hydrophobic ligand (TOPO) with the hydrophilic ligand on the surface of the quantum dots. Because DAET QDs are positively charged, they have been incorporated within negatively charged Nafion polymer. A major drawback of ligand exchange reactions is that they are commonly accompanied by a significant decrease in quantum yield. The quantum yield typically drops down in a range between 1%-25%, depending on the quantum yield before the ligand exchange. The quantum yield for the DAET-QD emission is determined to be less than 5% (Rhodamine 6G as reference).