Studies of magnetite nanoparticles synthesized by thermal decomposition of iron (III) acetylacetonate in tri(ethylene glycol)

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Abstract

In this paper, water-soluble magnetite nanoparticles have been directly synthesized by thermal decomposition of iron (III) acetylacetonate, Fe(acac)3 in tri(ethyleneglycol). Size and morphology of the nanoparticles are determined by transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements while the crystal structure is identified using X-ray diffraction (XRD). Surface charge and surface coating of the nanoparticles are recognized using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectra (XPS) and zeta potential measurements. Magnetic properties are determined using vibrating sample magnetometer (VSM) and superconducting quantum interference device (SQUID) measurements. The results show that as-prepared magnetite nanoparticles are relatively monodisperse, single crystalline and superparamagnetic in nature with the blocking temperature at around 100 K. The magnetite nanoparticles are found to be highly soluble in water due to steric and electrostatic interactions between the particles arising by the surface adsorbed tri(ethyleneglycol) molecules and associated positive charges, respectively. Cytotoxicity studies on human cervical (SiHa), mouse melanoma (B16F10) and mouse primary fibroblast cells demonstrate that up to a dose of 80 μg/ml, the magnetic nanoparticles are nontoxic to the cells. Specific absorption rate (SAR) value has been calculated to be 885 and 539 W/gm for samples with the iron concentration of 1 and 0.5 mg/ml, respectively. The high SAR value upon exposure to 20 MHz radiofrequency signifies the applicability of as-prepared magnetite nanoparticles for a feasible magnetic hyperthermia treatment.

Introduction

Superparamagnetic (SPM) iron oxide (particularly Fe2O3 and Fe3O4) nanoparticles have been attracted a great attention in the bio-medical field such as magnetic separation, drug delivery, cancer hyperthermia and magnetic resonance imaging (MRI) contrast enhancement [1], [2], [3], [4], [5], [6]. The single-step synthesis of highly water-soluble, superparamagnetic and biocompatible magnetite nanoparticles with controlled size and distribution is extremely important to realize the full potential of these materials in biomedicine. To date, the thermal decomposition method is very promising technique to fabricate high-quality superparamagnetic and monodisperse magnetite nanoparticles [7], [8], [9]. Typically, this method involves decomposition of Fe(acac)3 in a high-boiling temperature solvent in presence of stabilizing surfactants such as oleic acid and oleylamine. However, the obtained magnetite nanoparticles are organic soluble which makes them inappropriate for bio-medical applications. Therefore, many groups have further developed the thermal decomposition method to directly synthesize water-soluble magnetic nanoparticles [10], [11]. Recently, Cai et al. [12] have synthesized water-soluble magnetite nanoparticles by high-temperature decomposition of Fe(acac)3 in triethylene glycol (TREG). An obvious advantage of this approach is that no further reducing agent and surfactants are required, which made this process easy to scale-up for mass. The TREG has been used for a triple role as high-boiling solvent, reducing agent and stabilizer to efficiently control the particle growth and prevent interparticle aggregation. Here, we have extended this work and proposed a mechanism for solubility of the as-prepared magnetite nanoparticles in aqueous suspension by exploring surface charge and surface coating of the nanoparticles. Cytotoxicity and hyperthermia studies of the nanoparticles have also been performed to evaluate their potentiality in biomedicine.

Section snippets

Experimental section

Absolute ethanol and ethyl acetate were used without purification. Tri(ethylene glycol) (TREG, 99%) and Iron(III) acetylacetonate (Fe(acac)3, 97%) were purchased from Sigma-Aldrich.

Water-soluble Fe3O4 nanoparticles were prepared by the thermal decomposition of Fe(acac)3 in TREG at elevated temperature with out using any surfactants [12]. Typically, 2 mmol of Fe(acac)3 was dissolved in a 20 ml of hydrophilic TREG media and then magnetically stirred under a flow of argon. The solution was

Crystal structure

Fig. 1 shows the XRD patterns which match well with the standard XRD patterns for bulk magnetite (JCPDS File no. 19-0629) indicating that the particles are consisting of Fe3O4 phase. The average crystallite size is measured using Scherrer's equation [15] as 10.7 nm.

Size and morphology

The TEM image in Fig. 2 indicates that the magnetite nanoparticles are well dispersed in water. The average size of the particle is about 11 nm which is very close to the crystallite size obtained from XRD. Inset of Fig. 7 is showing

Conclusions

As-prepared magnetite nanoparticles are relatively monodisperse, single crystalline and superparamagnetic in nature. The nanoparticles are highly soluble in water because of the steric and electrostatic interactions between the particles arise from the surface adsorbed tri(ethyleneglycol) molecules and the associated positive charges, respectively. Cytotoxicity studies show that as-prepared magnetite nanoparticles are biocompatible up to the iron concentration of 80 μg/ml. The significant

Acknowledgments

The authors gratefully acknowledge the help of Dr. S.D. Dhole, Department of Physics, University of Pune, for the hyperthermia heating measurement.

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