Effects of surfactants on the magnetic properties of iron oxide colloids

Iron oxide nanoparticles are having been extensively investigated for several biomedical applicationssuch as hyperthermia and magnetic resonance imaging. However, one of the biggest problems of thesenanoparticles is their aggregation.Taking this into account, in this study the influence of three different surfactants (oleic acid, sodiumcitrate and Triton X-100) each one with various concentrations in the colloidal solutions stability wasanalyzed by using a rapid and facile method, the variation in the optical absorbance along time.The synthesized nanoparticles through chemical precipitation showed an average size of 9 nm and anarrow size distribution. X-ray diffraction pattern and Fourier Transform Infrared analysis confirmedthe presence of pure magnetite. SQUID measurements showed superparamagnetic properties with ablocking temperature around 155 K. In addition it was observed that neither sodium citrate nor TritonX-100 influences the magnetic properties of the nanoparticles. On the other hand, oleic acid in a concen-tration of 64 mM decreases the saturation magnetization from 67 to 45 emu/g. Oleic acid exhibits a goodperformance as stabilizer of the iron oxide nanoparticles in an aqueous solution for 24 h, for concentra-tions that lead to the formation of the double layer.