Quantum Dots for Biological Probing

Quantum dots (QDs) are semiconductor nanocrystals that can be used to probe biological molecules inside the cell. They are composed of a Cadmium Selenide (CdSe) core and a Zinc Sulfide (ZnS) outer shell. QDs have the potential to surpass the functionalities of conventional organic fluorophores. In contrast to tradition organic flurohores, QDs are superior in brightness, resistant to photobleaching, and have a tunable fluorescence emission, which is size-dependent. However, QDs bind nonspecifically to non-targeted molecules in the cell. A way to solve this problem is to alter the coater ligands on the QDs. Molecules with a thiol functional group were chosen to coat the QDs because sulfur makes a coordination bond with the ZnS outer shell.  Coaters were also chosen based on their charge, biocompatibility, flexibility, and the reactivity of their functional groups. Gel Electrophoresis was used to evaluate the charge of the coated QDs. A circular dichroism (CD) assay suggests that the QD coaters do not affect the secondary structure of Anti-mouse Immunoglobulin G (made in goat). The binding specificity was evaluated with tubulin in fixed HeLa cells. In a control experiment, a clear structure was obtained with Alexa 647 organic fluorophore incubated in Glutathione, Cysteine, and 4-pegylated mercaptoundecanol (PEG-4). Further studies will evaluate the effects of the coated QDs on the functions of the antibodies and insight into the biological compatibility of these coated QDs.