Quantum dot labeling of membrane associated targets: The development of small molecule conjugates to interrogate the serotonin transporter protein

The primary aim of this research was to incorporate highly fluorescent semiconductor nanocrystals, or quantum dots (QDs), in various biological assays as an improved means of optically imaging membrane associated receptors. Initial imaging efforts utilized antibody conjugated QDs to fluorescently label interleukin-2 receptor (IL-2R) expression in activated populations of Jurkat T cells, ultimately permitting verification of the time-course associated with IL-2R translation and expression. The remainder of the research was focused on the development of a small molecule QD targeting strategy to generate fluorescent probes capable of specifically interacting with the serotonin transporter protein. Attempts to functionalize ampiphilic QDs with custom synthesized small molecule-polyethylene glycol derivatives possessing a hydrophobic terminus initially resulted in self assembly of these ligands to the QD surface in the absence of covalent coupling reagents. The artifactual fluorescent response caused by protein adsorption in biological assays, as well as considerations for improved small molecule presentation as a means to facilitate specific QD interactions were subsequently identified. Finally, an optimized protocol which ultimately permits the fluorescent detection of serotonin transporter expression in live mammalian cell cultures using both fluorescent microscopy and flow cytometry has been described.