We report here on covalent functionalization of magnetic narroparticle colloidal suspension (ferrofluid) with doxorubicin. Since doxorubicin (adriamycin) is a potent anti-cancer drug, such particles can be guided with external magnetic field to a target tissue, a carrier process that may overcome the non-specificity and efficiency of adriamycin as a drug. The nanoferrite functionalization was effected by means of acid chloride chemistry leading to the formation of covalent bond between the hydroxyl groups at the nanoparticle surface and acid chloride molecules. This procedure can be easily tailored to provide the nanoferrites with various functionalities capable of further modifications with, e.g., drug molecules. Thus, we used such modified nanoferrites to covalently attach molecules of anti-tumor drug-doxorubicin. The attachment was verified by means of FTIR and cyclic voltammetry. Mean size of nanoferrites was evaluated by powder X-ray diffraction (PXRD) technique and high-resolution field emission scanning electron microscope (HR-FESEM). The amount of doxorubicin attached to nanoparticles was assessed by means of quartz crystal microbalance combined with cyclic voltammetry. (C) 2008 Elsevier Ltd. All rights reserved.