Synthesis and characterization of magnetic nanoparticles for use as sensors

Abstract

A comprehensive study of physical and magnetic properties of cobalt substituted ferrite and magnetite nanoparticles synthesized by thermal-decomposition was carried out. Initially, a systematic study of the effect of synthesis conditions on final size, crystalline structure, and composition of cobalt substituted ferrite nanoparticles synthesized by thermal-decomposition was carried out. Using a statistical design of experiments, the impact of the temperature and time during nucleation and growth stages on final particle size, lattice parameter, and Fe/Co ratio was determined. Based on DC and AC susceptibility measurements, the effect of sample preparation on determination of the anisotropy constant of magnetite nanoparticles was studied. Magnetite nanoparticles synthesized by the thermal-decomposition method were fixed in a poly(styrene-divinylbenzene) matrix at 0.1%, 1%, and 6%(w/w). ZFC curves and the out-of-phase component of the dynamic susceptibility were obtained for each of sample and using Néel and Vogel-Fulcher models, the anisotropy constant was determined. The effect of particle size on the anisotropy constant of magnetite nanoparticles was also studied. In this case, magnetite with different diameter were synthesized by vary the synthesis conditions during thermal-decomposition method. Magnetite nanoparticles were fixed in poly(styrene-divinylbenzene) at 0.1% (w/w) and ZFC curves and AC susceptibility measurements were carried out Finally, cobalt ferrite nanoparticles synthesized by the thermal-decomposition method were tested as possible sensors. Cobalt ferrite nanoparticles were functionalized with biotin using a COO- -silane coupling agent. Using AC measurements, avidin molecules at a concentration of 1 μM in aqueous solution could be detected by monitoring the change in Brownian relaxation time after the attachment of avidin molecule to biotinylized cobalt ferrite nanoparticle. This analysis required a sample volume of 100 μl and on 8 μg of the protein to be detected.