Magnetic and Cytotoxicity Properties of La1−xSr x MnO3(0 ≤ x ≤ 0.5) Nanoparticles Prepared by a Simple Thermal Hydro-Decomposition
© to the authors 2009
Received: 23 December 2008
Accepted: 14 April 2009
Published: 9 May 2009
This study reports the magnetic and cytotoxicity properties of magnetic nanoparticles of La1−xSr x MnO3(LSMO) withx = 0, 0.1, 0.2, 0.3, 0.4, and 0.5 by a simple thermal decomposition method by using acetate salts of La, Sr, and Mn as starting materials in aqueous solution. To obtain the LSMO nanoparticles, thermal decomposition of the precursor was carried out at the temperatures of 600, 700, 800, and 900 °C for 6 h. The synthesized LSMO nanoparticles were characterized by XRD, FT-IR, TEM, and SEM. Structural characterization shows that the prepared particles consist of two phases of LaMnO3(LMO) and LSMO with crystallite sizes ranging from 20 nm to 87 nm. All the prepared samples have a perovskite structure with transformation from cubic to rhombohedral at thermal decomposition temperature higher than 900 °C in LSMO samples ofx ≤ 0.3. Basic magnetic characteristics such as saturated magnetization (MS) and coercive field (HC) were evaluated by vibrating sample magnetometry at room temperature (20 °C). The samples show paramagnetic behavior for all the samples withx = 0 or LMO, and a superparamagnetic behavior for the other samples havingMSvalues of ~20–47 emu/g and theHCvalues of ~10–40 Oe, depending on the crystallite size and thermal decomposition temperature. Cytotoxicity of the synthesized LSMO nanoparticles was also evaluated with NIH 3T3 cells and the result shows that the synthesized nanoparticles were not toxic to the cells as determined from cell viability in response to the liquid extract of LSMO nanoparticles.
The perovskite manganites La1−xSr x MnO3 have recently attracted much attention because of their technical applications [1, 2]. Sr-doped LaMnO3 or LSMO is particularly of interest due to its good magnetic, electrical, and catalytic properties and nowadays is increasingly becoming an attractive possibility in several biomedical applications. A variety of methods has been attempted for the preparation of highly homogeneous and fine powders of these perovskite manganites, including the citrate-gel process , sol–gel route , molten salt method , autocombustion process , and hydrothermal synthesis , to name just a few. Among these established synthesis methods, it is still critical to find simple and cost effective routes to synthesize LSMO nanocrystalline with a well controlled, reproducible, and narrow size distribution of ferromagnetic nanoparticles with large magnetic moment per particle by utilization of cheap, nontoxic, and environmentally benign precursors.
In this paper, we report a simple and cost effective synthesis of La1−xSr x MnO3nanoparticles withx = 0, 0.1, 0.2, 0.3, 0.4, 0.5 by using the decomposition mechanism of metal acetate salts in water at various temperatures of 600–900 °C. The influence of Sr concentration on the structure and the morphology of the samples was characterized by XRD, FT-IR, SEM, and TEM. Magnetic properties of the samples were investigated by vibrating sample magnetometer (VSM). The effects of Sr concentration and thermal decomposition temperature on the magnetic properties were also discussed in detail. The last part of the investigation concerns the result of cytotoxicity testing of the synthesized sample by MTT assay.
Magnetic nanoparticles of La1−xSr x MnO3(LSMO) withx = 0, 0.1, 0.2, 0.3, 0.4, 0.5 were prepared via the thermal hydro-decomposition method. In this process, high purity acetates of La(CH3COO)3 · x H2O (99.9%, Aldrich), Mn(CH3COO)2 · 4H2O (>99.9%, Fluka), and Sr(CH3COO)2(99%, Aldrich) were used as starting materials. In a typical procedure, 0.007 mol metal acetates with a mole ratio corresponding to the nominal composition of La: Sr: Mn ratio of 1−x: x: 1 were dissolved in deionized water (DI water) at a ratio of 5:1 (volume/weight) of DI water to total acetate salts. The mixed solution was stirred with a magnetic stirrer at room temperature for 15 min, and was thermally decomposed in an oven under normal atmosphere at different temperatures of 600, 700, 800, and 900 °C for 6 h and left to cool down to room temperature before being ground to obtain LSMO nanoparticles.
The crystal structure of the synthesized LSMO nanoparticles was characterized by X-ray diffraction (XRD) (Philips PW3040, The Netherlands) with the crystallite size calculated from the broadening of the XRD peaks using Debye–Scherrer method. The functional groups present in the samples were studied using the Fourier Transform Infrared Spectroscopy technique (FT-IR) (Spectrum one, Perkin Elmer Instrument, USA). The samples were incorporated in KBr pellets for which the FT-IR spectra were obtained in the 1000–450 cm−1wave-number range. The morphology of the samples was revealed by scanning electron microscopy (SEM) (LEO 1450VP, UK) and transmission electron microscopy (TEM) (JEOL 2010, 200 kV, Japan). The selected area electron diffraction (SAED) patterns from TEM and high resolution TEM (HRTEM) images were analyzed to identify the phase and crystal structure, and to confirm the results obtained from XRD. The magnetic properties were investigated by Vibrating Sample Magnetometer (VSM) (Lakeshore 7403, USA) at room temperature (20 °C).
The cytotoxicity of LSMO nanoparticles was evaluated with NIH 3T3 and cell viability was determined by MTT colorimetric assay (Sigma, USA). Cells were seeded on the 96-well culture plate (1 × 104 cells/well) for 24 h. The extracted LSMO liquid was taken by boiling LSMO particles in sterile distilled water at 121 °C for 1 h with concentration of 0.2 g/mL. Cells were incubated with 20 mL extracted LSMO liquid or sterile water (control) for 24 h. After removing the medium, 10 mL of 12 mM MTT solution was added and incubated for a further 4 h. Blue formazan crystals, metabolized MTT in mitochondria of viable cells, were dissolved in 50 mL of dimethylsulfoxide (DMSO; Sigma, USA) and measured at 550 nm by the plate reader (Biorad, Japan). The average value of four wells was used for each sample and two repeats were done in each experiment. The control NIH 3T3 cell viability was defined as 100%. Statistical comparison was performed using one-way ANOVA with SPSS software version 11.5 (SPSS, Germany).
Results and Discussion
Structural and Morphology Characterization
Properties of prepared LSMO
La1−xSr x MnO3
Thermally decomposed in the range of 700 → 900°C for 6 h
Cubic → Rhombo
Cubic → Rhombo
Cubic → Rhombo
Cubic → Rhombo
Crystallite size (nm)
LSMO nanoparticles with 0 ≤ x ≤ 0.5 have been synthesized by a simple thermal decomposition method using acetate salts in DI water. Structural characterization shows that the structure transforms from cubic to rhombohedral in the prepared samples withx ≤ 0.3 when decomposed at 900 °C, while the others remained cubic in structure. Study of magnetic properties at room temperature shows thatMSdepends strongly on the thermal decomposition temperature for samples ofx ≥ 0.2, and has no exact dependence on Sr concentration. There is a variation ofMSwith Sr content with the maximum atx = 0.3 for decomposition temperature of 900 °C, and at temperature below this the maximumMSof 40.4 emu/g is found atx = 0.2. In addition, the magnetic nanoparticles show no toxicity to the tested cells, NIH 3T3, as determined from the result of cell viability in response to the liquid extraction of the magnetic nanoparticles. This will be useful for medical applications. The present work has shown that the thermal hydro-decomposition is a new useful method for preparation of manganite nanoparticles, and gives a potential avenue for further practical scale-up of the production process and applications.
The authors would like to thank the Department of Chemistry of Khon Kaen University for providing FT-IR and VSM facilities, the Faculty of Science Electron Microscopy Unit for providing SEM facilities, and the National Metal and Materials Technology Center (MTEC) of NSTDA for providing TEM facilities. S. Daengsakul would like to thank the TGIST scholarship for the support of her Ph.D. study. This work is financially supported by The National Research Council of Thailand (NRCT) under the research contract no. PorKor/2550-287.
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