Sugar−Quantum Dot Conjugates for a Selective and Sensitive Detection of Lectins

Abstract

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.

Glyconanoparticles for colorimetric bioassays

“…Although different types of nanomaterials including CdS/ZnS quantum dots, [33][34][35][36][37][38] upconverting nanoparticles, 39 magnetic nanoparticles, [40][41][42][43][44][45] and carbon nanotubes, 46 have been used for the synthesis of glyconanoparticles, the intrinsic colour changes associated with the aggregation of noble metal nanoparticles have ensured that these nanoparticles are extensively used for the development of bioassays.…”

Fluorescently labelled glycans and their applications

“…It was determined that approximately 210 GlcNAc molecules were incorporated into each QD, and the fluorescence of the QDs is quenched in the presence of WGA lectin in a concentration-dependent fashion. In a similar approach, CdSe/ZnS QDs were decorated with glycans derived from di-or trisaccharides, e.g., D-lactose, D-melibiose, or D-maltotriose, through reductive amination, and investigated for their ability to agglutinate soybean agglutinin, jacalin, and Con A [124]. These glycandecorated QDs can selectively agglutinate corresponding lectins and the resulting aggregates can be deglutinated with free glycans selectively.…”

Multivalent glycoconjugates in medicinal chemistry

“…153 The specific interactions between soybean agglutinin and Con A with CdSe/ZnS glyco-QDs have been monitored using the light scattered at 600 nm. 154 Mannose-coated CdS quantum dots (Man-QDs) (Fig. 23) induce luminescent aggregates of E. coli which can be used to detect bacteria in cell suspensions, containing as few as 10 4 bacteria per mL.…”