Superparamagnetism of Magnetite Nanoparticles:  Dependence on Surface Modification

Abstract

Superparamagnetic iron oxide nanoparticles (SPION) with an average particle diameter of 6 nm are prepared by controlled chemical coprecipitations. Colloidal suspensions of noninteracting SPION, where the surface has been modified with three different types of biocompatible substances, namely, starch, gold (Au), and methoxypoly(ethylene glycol) (MPEG) have been fabricated via three different techniques. Starch-coated SPION are prepared by coprecipitation in a polymeric matrix, Au-coated SPION are fabricated by the microemulsion method, and MPEG-coated SPION are prepared using the self-assembly approach. The magnetic nanoparticles form a core-shell structure, and the magnetic dipole-dipole interactions are screened by a layer of coating agents. The amounts of coating agents and SPION are indirectly calculated from the thermogravimetric analysis and superconducting quantum interference device measurements by assuming passive oxidation on the surface of the SPION, and the other conditions do not influence the measurements. The dependency of the spectral characteristics of Mössbauer spectroscopy as a function of an external magnetic field Hext is measured to investigate the effect of dipole-dipole screening of the different coating layers on the SPION. Uncoated SPION show a stable magnetic moment under Hext, and the superparamagnetic (SPM) fraction transforms to a ferrimagnetic state. Starch and Au-coated SPION retain the SPM fraction according to Mössbauer spectroscopy and magnetization measurements. MPEG-coated SPION show hyperfine magnetic structure without the quadrupole effect with increasing the value of the blocking temperature.

Synthesizing Iron Oxide Nanostructures: The Polyethylenenemine (PEI) Role

“…The saturation magnetization M SAT , on the other hand, shows a linear trend from FeO_800 to the FeO_25000 and FeO_nopei samples, with M SAT values of 83 emu/g, 66 emu/g, and 11 emu/g, respectively. While the saturation value of the FeO_800 is lower, but still comparable to the bulk saturation value of 92 emu/g [35], the decrease observed in M SAT for the remaining samples can be at first attributed to the presence of the antiferromagnetic hematite phase, which causes a depression of the magnetization values normalized by mass. This effect can be already observed in the FeO_25000 sample, but becomes dramatic in the FeO_nopei sample.…”

Engineered inorganic core/shell nanoparticles

“…Indeed, gold shells grown on magnetite exhibit a surface plasmon resonance at larger wavelengths compared to shells of similar size grown over silica. In addition, this resonance is further red-shifted with increasing shell thickness, in contrast to the blue shift observed for shells grown over silica [78,201,202]. This lower energy resonance of the plasmon is related to the permittivity of the core (high for Fe oxide and low for silica) and its variation with increasing the size of the shell results from the decrease of the coupling between the shell plasmons associated with the outer and the inner side of the gold shell (figure 28).…”

“…(decrease) of the blocking temperature and a decrease in their susceptibility in comparison to the uncoated NPs, which is believed to reflect the less efficient coupling of the magnetic cores as a result of interparticle spacing [78,200,201,157] In contrast, the plasmonic properties of the metallic shell are strongly influenced by the high dielectric constant of the magnetic cores. Indeed, gold shells grown on magnetite exhibit a surface plasmon resonance at larger wavelengths compared to shells of similar size grown over silica.…”

Iron Oxide Biomagnetic Nanoparticles (IO-BMNPs); Synthesis, Characterization and Biomedical Application–A Review

“…Use laboratory equipments and different novel procedure for preparing Fe 3 O 4 nanoparticles and coating biocompatible materials on it, has been describing in numerous articles. In this research [24] FeCl 3 (0.5 mol/L) and FeSO 4 (0.5 mol/L) solutions provided individually and transferred into a three-neck round bottom flask equipped with a mechanical stirrer (magnetic stirrer). Immediately after adding the iron salt solutions, 5 mL NH 3 .H 2 O (50%, v/v aqueous) was quickly syringed into the flask with stirring.…”