High Heating Efficiency of Magnetite Nanoparticles Synthesized with Citric Acid: Application for Hyperthermia Treatment

We report in this work the magnetic, morphological, and heating properties of magnetite nanoparticles (MNPs), which were synthesized by using different molar aqueous solutions of citric acid and the combustion method. When the content of citric acid (molarity) is increased from 0.5 M to 2 M, the average size of MNPs decreased from 7.3 +/- 1 nm to 6.9 +/- 1 nm according to the microscopy analysis. Also, the analysis by x-ray diffraction confirmed that all the MNPs presented a cubic phase. On the other hand, the magnetic measurements of the magnetite nanoparticles showed that they are superparamagnetic, since their coercivity values are in the range of 3-9 Oe. The MNPs were subjected to a magnetic field of 0.1 T while the frequency was varied from 87 kHz to 340 kHz. After this, the specific absorption rate (SAR) was calculated (this parameter is relevant because it is related to the heating efficiency of the nanoparticles). Consequently, the highest SAR value (179.8 W/g) was obtained at a frequency of 87 kHz and the lowest SAR value (114.9 W/g) was obtained at a frequency of 340 kHz. Furthermore, the SAR values were correlated with the Fe2+/Fe3+ ratio and found that the increase of this ratio enhances the heating efficiency of the magnetite nanoparticles. Also, the maximum heating temperature of the MNPs increases with the molarity of the citric acid (at the same frequency of applied magnetic field). In general, the highest values of heating temperature (61.2-66.4 degrees C) were produced by the MNPs subjected to a magnetic field of 87 Hz. We also evaluated the toxicity of the MNPs by obtaining their viability % values and those were in the range of 86-95%, which means that they are non-toxic and biocompatible. We finally achieved a proof of concept (in vitro experiments) and attached MNPs to colon cancer cells. Subsequently, these were subjected to a magnetic field of 0.1 T at a frequency of 87 kHz and could destroy the cancer cells (as confirmed by optical images). Hence, the results of this research demonstrate that the MNPs studied here are promising candidates for hyperthermia treatment. [GRAPHICS] .