Effects of Coating and Stirring on Superparamagnetic Iron Oxide Nanoparticles Size and Magnetic Characteristics

Abstract

Considering the importance of nanoparticles physico-chemical properties in biomedical applications, we intend to describe and compares the results of fiveexperimental studies including: uncoated magnetic nanoparticles (MNPs), MNP + polyvinyl alcohol (PVA), MNP + amorphous silica (SiO 2 ) + gold (Au), and MNP + Au only. Controlled co-precipitation technique under N 2 gas is used to prevent undesirable critical oxidation of Fe 2+ .For uncoated Fe 3 O 4 NPs with saturation magnetization (M s ) range of (40-100) emu/g, smaller particles are synthesized by decreasing the NaOH concentration and increasing the stirring speed with the smallest value corresponding to 7.5 nm using 0.9 M of NaOH at 1500 rpm. The coatingprocess is done in four separate steps as follows:(i) the stable magnetic fluid containing well-dispersed Fe 3 O 4 /PVA nanocomposites which indicates a fast magnetic response with the smallest value of 7.5 nm using 0.9 M of NaOH at 750 rpm and M s of 50 emu/g, (ii) the synthesized Fe 3 O 4 NPs are stabilized using trisodium citrate (TSC) coating and then covered by SiO 2 layer using Stober method with the smallest value of 50 nm using 0.9 M of NaOH at 750 rpm and M s of 30 emu/g, (iii) small gold colloids (1-3 nm) are synthesized using Duff method and covered the amino functionalized particle surface of Fe 3 O 4 /SiO 2 nanoshells with the smallest value of 85 nm using 0.9 M of NaOH at 750 rpm and M s of 1.3 emu/g, (iv) also, bare superparamagneticIron oxide NPs (SPIONs) are covered by a thin layer of gold alone with the smallest value of 16 nm using 0.9 M of NaOH at 1500 rpm and M s of 12 emu/g. Magnetic properties and size of nanoshells are assessed using vibrating sample magnetometer (VSM)and transmission electron microscope (TEM). Furthermore, M s of 7.5 nm magnetite is high enough to be used as contrast agent for photoacoustic (PAI) and magnetic resonance imaging (MRI).