Abstract
We have been developing optical nanoprobes based on glycoconjugated gold nanoparticles that selectively and sensitively detect carbohydrate–protein interactions. Nanoparticle aggregations induced by specific carbohydrate–protein interactions shift plasmon absorption to longer wavelengths and increase plasmon light scattering. The dissociation constants (Kd) for carbohydrate–protein interactions were calculated from UV-Vis spectral data by performing computer simulations and assuming aggregates with a protein : glycoconjugated gold nanoparticle ratio of 1 : 2. The obtained Kd values were much higher than those of monosaccharaides. These results reveal that the presence of multiple carbohydrate ligands on gold nanoparticle surfaces significantly enhances the affinity for carbohydrate-binding proteins relative to that for monosaccharaides. Carbohydrate-binding proteins can be detected with a high sensitivity using such glycoconjugated gold nanoparticles. In this method based on plasmon absorption, the maximum wavelength shifts are proportional to the mannose-binding protein (Concanavalin A) concentration in the range of 12–45 nM ; the limit of detection (LOD) was 4.0 nM. The detection sensitivity can be further enhanced by using a method based on plasmon light scattering ; the corresponding LOD for Concanavalin A was 0.4 nM.
