Garaio Eneko, Sandre Olivier, Collantes Juan-Mari, Garcia Jose Angel, Mornet Stéphane, Plazaola Fernando
Elektrizitatea eta Elektronika Saila, UPV/EHU, P.K. 644, Bilbao, Spain.
Nanotechnology. 2015 Jan 9;26(1):015704. doi: 10.1088/0957-4484/26/1/015704. Epub 2014 Dec 9.
Magnetic nanoparticles (NPs) are intensively studied for their potential use for magnetic hyperthermia, a treatment that has passed a phase II clinical trial against severe brain cancer (glioblastoma) at the end of 2011. Their heating power, characterized by the 'specific absorption rate (SAR)', is often considered temperature independent in the literature, mainly because of the difficulties that arise from the measurement methodology. Using a dynamic magnetometer presented in a recent paper, we measure here the thermal dependence of SAR for superparamagnetic iron oxide (maghemite) NPs of four different size-ranges corresponding to mean diameters around 12 nm, 14 nm, 15 nm and 16 nm. The article reports a parametrical study extending from 10 to 60 °C in temperature, from 75 to 1031 kHz in frequency, and from 2 to 24 kA m(-1) in magnetic field strength. It was observed that SAR values of smaller NPs decrease with temperature whereas for the larger sample (16 nm) SAR values increase with temperature. The measured variation of SAR with temperature is frequency dependent. This behaviour is fully explained within the scope of linear response theory based on Néel and Brown relaxation processes, using independent magnetic measurements of the specific magnetization and the magnetic anisotropy constant. A good quantitative agreement between experimental values and theoretical values is confirmed in a tri-dimensional space that uses as coordinates the field strength, the frequency and the temperature.
磁性纳米颗粒（NPs）因其在磁热疗中的潜在应用而受到广泛研究，磁热疗作为一种治疗方法，在2011年底已针对严重脑癌（胶质母细胞瘤）通过了II期临床试验。其加热功率以“比吸收率（SAR）”为特征，在文献中通常被认为与温度无关，主要是由于测量方法存在困难。利用最近一篇论文中介绍的动态磁力计，我们在此测量了四种不同尺寸范围的超顺磁性氧化铁（磁赤铁矿）纳米颗粒的SAR与温度的关系，这些纳米颗粒的平均直径分别约为12nm、14nm、15nm和16nm。本文报道了一项参数研究，温度范围从10到60°C，频率范围从75到1031kHz，磁场强度范围从2到24kA m⁻¹。观察到较小纳米颗粒的SAR值随温度降低，而对于较大的样品（16nm），SAR值随温度升高。测量得到的SAR随温度的变化与频率有关。基于奈尔和布朗弛豫过程的线性响应理论，利用比磁化强度和磁各向异性常数的独立磁测量，在该范围内对这种行为进行了充分解释。在以场强、频率和温度为坐标的三维空间中，实验值与理论值之间证实了良好的定量一致性。
