The present invention relates to nanoparticles with tumor necrosis factor (TNF) or cytokine immobilized thereon, where TNF or the cytokine is preferably immobilized in the form of a trimer in directed fashion and with retention of its biological activity on the carrier, to methods for the directed immobilization of TNF or cytokine on nanoparticles, to the use of the nanoparticles having immobilized TNF or cytokine for the identification and/or isolation of cytokine- or TNF-binding partners and for the identification and/or isolation of inhibitors of the interaction between TNF or cytokine and its binding partners, to the use of such nanoparticles for preparing a pharmaceutical composition, in particular for the therapy of tumors, and to pharmaceutical and diagnostic compositions which comprise such nanoparticles.