Size-sorted anionic iron oxide nanomagnets as colloidal mediators for magnetic hyperthermia
Size-sorted anionic iron oxide nanomagnets as colloidal mediators for magnetic hyperthermia
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DOI：
10.1021/ja067457e
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发表时间：
2007-03-07
影响因子：
15
通讯作者：
Gazeau, Florence
中科院分区：
文献类型：
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作者：
Fortin, Jean-Paul;Wilhelm, Claire;Gazeau, Florence
氧化铁胶体纳米磁体在交变磁场作用下产生热量。它们的加热功率由单畴粒子（布朗弛豫和尼尔弛豫）的磁能耗散机制决定，对晶体尺寸、材料和溶剂性质高度敏感。本研究旨在区分尼尔机制和布朗机制对热生成的贡献。采用化学方法合成磁性各向异性不同的磁铁矿和钴铁氧体阴离子纳米晶体，并通过静电稳定技术将其分散在水悬浮液中。通过连续的静电相分离步骤对颗粒进行粒度排序。控制纳米磁体作为热介质效率的参数是独立变化的；这些参数包括粒径（5 ~ 16.5 nm）、溶剂粘度、磁性各向异性以及磁场频率和振幅。测量的比损失功率（slp）与考虑了尼尔和布朗损失过程以及整个粒径分布的预测模型的结果在定量上一致。通过改变载流体粘度，我们发现载流体内部的布朗摩擦是铁酸钴颗粒发热能力的主要贡献者。相比之下，尼尔内旋的磁矩占磁铁矿颗粒损失功率的大部分。随着磁铁矿晶体尺寸的增大，比损耗功率变化了3个数量级（在700 kHz和24.8 kA/m下从4到1650 W/g）。这项综合参数研究为利用阴离子胶体纳米晶体在各种介质（包括复杂系统和生物材料）中产生磁诱导热疗提供了基础。
Iron oxide colloidal nanomagnets generate heat when subjected to an alternating magnetic field. Their heating power, governed by the mechanisms of magnetic energy dissipation for single-domain particles (Brown and Neel relaxations), is highly sensitive to the crystal size, the material, and the solvent properties. This study was designed to distinguish between the contributions of Neel and Brownian mechanisms to heat generation. Anionic nanocrystals of maghemite and cobalt ferrite, differing by their magnetic anisotropy, were chemically synthesized and dispersed in an aqueous suspension by electrostatic stabilization. The particles were size-sorted by successive electrostatic phase separation steps. Parameters governing the efficiency of nanomagnets as heat mediators were varied independently; these comprised the particle size (from 5 to 16.5 nm), the solvent viscosity, magnetic anisotropy, and the magnetic field frequency and amplitude. The measured specific loss powers (SLPs) were in quantitative agreement with the results of a predictive model taking into account both Neel and Brown loss processes and the whole particle size distribution. By varying the carrier fluid viscosity, we found that Brownian friction within the carrier fluid was the main contributor to the heating power of cobalt ferrite particles. In contrast, Neel internal rotation of the magnetic moment accounted for most of the loss power of maghemite particles. Specific loss powers were varied by 3 orders of magnitude with increasing maghemite crystal size (from 4 to 1650 W/g at 700 kHz and 24.8 kA/m). This comprehensive parametric study provides the groundwork for the use of anionic colloidal nanocrystals to generate magnetically induced hyperthermia in various media, including complex systems and biological materials.