A synthesis of polyethylene glycol (PEG)-coated magnetite Fe₃O₄ nanoparticles and their characteristics for enhancement of biosensor

The magnetite Fe₃O₄ nanoparticles were synthesized by using chemical co-precipitation method and these nanoparticles were successfully coated by polyethylene glycol (PEG) with variation concentrations of PEG. The magnetite Fe₃O₄ nanoparticles used as a bimolecular label (nano-tags), exhibiting a soft magnetic behavior with magnetization (M _s) of 77.16 emu g⁻¹ and coercivity (H _c) of 50 Oe respectively. The polyethylene glycol (PEG) was used as a biocompatible polymer. The x-ray diffraction (XRD) patterns of the Fe₃O₄ showed that Fe₃O₄ was well crystallized. It also confirmed the existence of invers spinel. The diffraction peak of 35.4° was used to calculate the crystallite size. The estimation of Fe₃O₄ average crystallite size is 12 nm, while the PEG-coated Fe₃O₄ nanoparticles is 8.6 nm. The transmission electron microscopy (TEM) images of Fe₃O₄ showed that the morphology of magnetite Fe₃O₄ nanoparticle is spherical in shape with uniform grain size and good dispersibility despite the agglomeration it found in some place. The addition of PEG can decrease the agglomeration and reduce the particle size. The existence of PEG layer on Fe₃O₄ was confirmed by Fourier transform infrared (FTIR) spectroscopy. The result of Vibrating Sample Magnetometer (VSM) showed that saturation magnetization (M _s) of Fe₃O₄ nanoparticles decreased from 77.16 to 37.15 emu g⁻¹ with the increase of PEG weight from 0% to 50%. Such Fe₃O₄ nanoparticles with favorable size and tunable magnetic properties are promising biosensor applications. (paper)