Chapter 20 De Novo Synthesis of Biofunctional Carbohydrate-Encapsulated Quantum Dots

摘要

Semiconductor nanocrystals, also called quantum dots (QDs) are particles that exhibit unique size- and composition-dependent optical properties. Several recent reports have described the synthesis of QDs coated with a variety of biomolecules for cellular imaging applications. We have prepared QDs coated with the tumor-associated carbohydrate antigen (TACA) disaccharide Galβ1-3GalNAcα- (Thomsen Friedenreich antigen) O-conjugated to various linkers and studied their photoluminescent and binding properties. The de novo synthesis of highly stable, luminescent and functional quantum dots was achieved by the use of a "hybrid" system containing small percentages of different surface passivating agents along with an appropriate neoglycoconjugate. The glycan-coated quantum dots were prepared in a simple one-pot procedure that is amenable to various other saccharides. Initial studies with thiolacetic acid as a co-capping agent produced highly luminescent particles with functional carbohydrate units but the negative charge was undesirable for important applications such as cellular bioimaging. Replacement of this small organic acid with a short modified polyethylene glycol segment yielded quantum dots with very similar properties butrnlacking charged functionality on the surface. An array of binding and agglutination assays confirmed that the functional characteristics of the sugar were intact on all particles synthesized. These new tools hold great promise for labeling cells that express specific carbohydrate-binding proteins on their surfaces.