The formation of a hybrid metal-biopolymer material is described. The synthesis of this material consists of functionalizing the surface of gold nanoparticles through a series of steps that lead to epoxy-functionalized nanoparticles. These are subsequently reacted with hydroxyl moieties of the alpha-D-glucopyranosyl groups of dextran. Subsequently, the dextran chains are carboxylated through treatment with bromoacetic acid. The resultant material combines the unique optical properties of gold nanoparticles with the versatility that carboxylated dextran offers for further functionalization with biomolecules. The interaction of this material with three proteins was then investigated through changes in the plasmon resonance properties of the gold nanoparticles. Concanavalin A, a lectin that binds glucose and mannose by means of specific molecular recognition, interacts readily with this material and such interaction is easily detected using optical absorption spectroscopy. Through reaction of the carboxyl groups with (+)-biotinyl-3,6,9,-trioxaundecanediamine, a material bearing biotin groups was obtained. This could interact with streptavidin or antibiotin by means of specific molecular recognition. Further confirmation of biospecific interactions was obtained with control experiments in which the binding sites were blocked through preincubation of the proteins with the corresponding ligand in solution. Binding of these proteins was concentration-dependent over a wide concentration range. This material provides a simple and convenient colorimetric method for biospecific interaction analysis.