Intellectual merit. When proteins are tagged with reporter labels to trace the locations and movements of the proteins on or within cells, the physical size of the label can be quite significant. This is especially true for the popular class of labels called quantum dots (qdots), which are inorganic crystals with intense fluorescence. The core of a qdot is fairly small, 2-4 nm, but is completely insoluble. To make them soluble in water-based buffers requires a hydrophobic-hydrophilic ligand shell. Commercially-available qdots are typically 21 nm in diameter. The research will make a ligand-shield that is only about 2 nm thick. The shield will have a sulfur atom that binds the qdot-core very tightly. This sulfur will either be a thiol, a thioether, or a thioketone. This sulfur will also have a polyethylene glycol, making the entity water soluble. It may have a negative or positive charge to reduce non-specific sticking. Finally, it will have a bioreactive entity for coupling.
Broader Impacts. Quantum dots have tremendous potential as incredibly bright fluorophores for labeling proteins. However, their large size has limited their usefulness as biological tracers. The research presented here intends to overcome this limitation by providing to the research community methods to make a new class of water-soluble quantum dots that are significantly smaller than those currently commercially available. The research provides excellent training for synthetic chemists and graduate students who are interested in basic optics, microscopy, and spectroscopy.
