Effect of Surfactants on Colloidal Stability and Magnetic Hyperthermia of Fe3O4 Nanoparticles

Abstract

In recent years, magnetic hyperthermia has emerged as promising therapy for the treatment of cancer. Use of Fe3O4 nanoparticles for in-vivo magnetic hyperthermia therapy has been approved by US food and drug administration (FDA). Fe3O4 nanoparticles have strong tendency to aggregate because of their high surface energy. Dipolar interactions between nano-crystallites further promote aggregation. This minimizes colloidal stability of nanoparticles and could deteriorate their magnetic hyperthermia performance. To minimize effect of dipolar interactions between nanoparticles, they are sterically stabilized by small chain surfactants. In this study we have studied effect of anionic (oleic acid) and cationic (CTAB) surfactants on colloidal stability and hyperthermia performance of Fe3O4 nanoparticles. Fe3O4 nanoparticles were synthesized by chemical co-precipitation method. They were coated with a bilayer of oleic acid (OA) or CTAB and dispersed in water. As-synthesized Fe3O4 nanoparticles are superparamagnetic with near zero coercivity and remanence. Colloidal stability of OA or CTAB coated Fe3O4 nanoparticles were determined by hydrodynamic size and zeta potential measurements. The hydrodynamic size of OA coated Fe3O4 nanoparticles show minimal change in 30 days aging. It increases from 40.5 nm to 41.7 nm, while their zeta potential changes from -65 mV to -52.50. In case of CTAB coated Fe3O4 nanoparticles, hydrodynamic size increases from 64.6 nm to 73.8 nm and zeta potential also increases to 56 mV from 40 mV within 30 days of aging. Optimum conditions of magnetic hyperthermia measurements of OA and CTAB coated Fe3O4 nanoparticles were established by performing measurements as a function of magnetic field strength (2-10 mT), field frequency (162-935.6 kHz) and nanoparticle concentration for 10 mins. Specific loss power (SLP) of OA coated Fe3O4 decreases from 14.94 W/g to 10.05 W/g while it remains almost constant (9.67 W/g to 9.39 W/g) in CTAB coated Fe3O4 aged for 30 days. Thus, CTAB coated Fe3O4 nanoparticles possess better colloidal stability and hence more suitable for magnetic hyperthermia applications.