Semiconductor Quantum Dots Water Solubilization, Functionalization, and Ratiometric Sensing of O2
Research on fluorescent semiconductor quantum dots (QDs, or nanocrystals) has been focused towards developing analytical applications for which their robust optical properties add value. To this end, the materials must be efficiently water solubilized and functionalized. This thesis details my research in this regard, starting with the development of a one-step method to produce ~10 nm hydrodynamic diameter water-soluble CdSe/ZnS quantum dots through ligand exchange with a near-monolayer of organosilane caps. The samples are stable for months under benchtop conditions and have high quantum yields (~60%), which is unprecedented for cap-exchanged QDs. Furthermore, the procedure can be applied to CdS/ZnS, ZnSe/ZnMnS/ZnS, and CuInS2/ZnS QDs. While water-solubilization is necessary for the development of analytical applications, the materials must be functionalized with chemical and biological vectors for sensing applications. In this regard, small molecular reagents that can efficiently functionalize water soluble CdSe/ZnS nanocrystals have been developed. These reagents do not cause quenching or precipitation of QDs as observed with commercially available activators. Last, a ratiometric fluorescent QD reporter for O2 levels in water created by attaching multiple pyrene-functional chromophores to the surface of bright, water-soluble semiconductor nanocrystals. These ligands have been used with both CdSe/CdZnS and AgInS2/ZnS nanocrystals, the latter of which represents a fluorescent QD sensor with significantly reduced toxicity.