This publication discloses a method and apparatus for functionalizing nanoparticle systems. The method comprises treating a nanoparticle-containing layer (102) so as to produce a pattern of structurally transformed zones, the treatment comprising applying an electric field through the nanoparticle layer (102). According to the invention an AC-field capacitively coupled to the nanoparticle-containing layer (102) is used as said electric field. The treatment preferably results in at least partly sintered structures, which can be used as conductors, for example. The document discloses several realizations for utilization of the disclosed functionalization in mass-fabrication lines.