Sugar-quantum dot conjugates for a selective and sensitive detection of lectins

One-pot synthesized neoglycoconjugates with a reactive thiol group are introduced here for functionalization with carbohydrates for solubilization and stabilization of CdSe-ZnS quantum dots in aqueous solution. Three different sizes of quantum dots (QDs) with lactose, melibiose, and maltotriose on their surface have been utilized, for the first time, for lectin detection through agglutination assay. The sugar-QDs thus synthesized were characterized by transmission election microscopy (TEM), fluorescence, and absorption spectroscopy. Agglutination of sugar-QDs by three different lectins occurred through specific multivalent carbohydrate-lectin interactions and was studied extensively by monitoring the scattered light at 600 nm. This assay was very selective, which has been demonstrated by a more selective binding of soybean agglutinin (SBA) with melibiose-QD, as compared to lactose-QD, and specific deagglutination caused by alpha-D-galactose, while alpha-D-mannose did not show any effect. The detection sensitivity of the maltotriose-QD was tested with Concanavalin A (ConA), and as little as 100 nM of the lectin was detected using light scattering. The detection sensitivity of this protocol has been enhanced considerably by the fluorescence properties of QDs. This agglutination process seems to occur through formation of smaller soluble aggregates, which further associate to form larger aggregates.