We report here a novel and simple approach on which nanometer-size, water soluble glycodendrimer (mannose-functionalized poly(amidoamine) PAMAM generation G0 cystamine core dendrimer) coated gold nanoparticles (Au–man) allows the detection of protein–carbohydrate interactions based on surface energy transfer process (SET). This sensitive SET sensing approach enables quantitative analysis of the binding constant of a mannose-binding protein, lectin Concanavalin A (Con A) labelled with a fluorophore to a sensing Au–man in aqueous samples. Competitive binding and inhibition assays were done to investigate the SET efficiency. The binding constant of Con A to Au–man interactions of (5.6 ± 0.1) × 10⁶ M⁻¹ is 100-times higher than the binding constant values obtained in the interactions with the glycodendrimer G2 alone. The simple modification of the gold nanoparticles with glycodendrimers provides a convenient method to obtain biocompatible and selective carbohydrate-based SET probes for protein biorecognition.