Method for manufacturing surface enhanced Raman spectroscopy tags

A method for manufacturing surface enhanced Raman spectroscopy (SERS) tags comprising the steps:

• a) providing a first colloid consisting essentially of nanoparticles having a plasmonic surface and substantially same size dispersed in an aqueous solvent, and a stabilizing agent adsorbed on the surface of said nanoparticles, and having a ζ-potential value lower than or equal to −25 mV;
• b) providing a second colloid consisting essentially of nanoparticles having a plasmonic surface and substantially same size dispersed in an aqueous solvent, Raman active reporter molecules adsorbed on the surface of said nanoparticles, and a stabilizing agent adsorbed on the surface of said nanoparticles, and having ζ-potential value lower than or equal to −25 mV;
• c) combining the first colloid with the second colloid so that the ratio between the number of nanoparticles of the first colloid and the number of nanoparticles of the second colloid is between about 25:1 to about 1:1, to provide a third colloid;
• d) inducing aggregation of the nanoparticles by any of the steps d1)-d3) or a combination thereof:
• d1) mixing the third colloid obtained at step c) at a pH comprised between about 2.2 and the lowest pH value at which the Raman active reporter molecules have a net electrical charge of between 0 and 0.3;
• d2) addition of a salt solution to the third colloid obtained at step c);
• d3) addition of a water-miscible solvent to the third colloid obtained at step c);
• and
• e) stopping aggregation.