A method for producing nanomaterial product which comprises at least one nanoparticle Gold-metal-Polymer, the polymer comprising at least one biopolymer, the atoms of metal being linked with the atom of Gold, the metal being chosen among: Gd, Co, Eu, Tb, Ce, Mn, Fe, Zn, Ag, the method being realized in an aqueous solvent, without reactive or stabilizer agent, and presenting a step of reducing: tetrachloroauric acid (HAuCl4) and metal ions, in the presence of the biopolymer, the biopolymer being used as a stabilizer agent.