Ovejero Jesus G, Spizzo Federico, Morales M Puerto, Del Bianco Lucia
Dept. Energía, Medio Ambiente y Salud, Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, E-28049 Madrid, Spain.
Nanoscale. 2021 Mar 21;13(11):5714-5729. doi: 10.1039/d0nr09121a. Epub 2021 Mar 11.
Tuning the magnetic properties of nanoparticles is a strategic goal to use them in the most effective way to perform specific functions in the nanomedicine field. We report a systematic study carried out on a set of samples obtained by mixing together iron oxide nanoparticles with different shape: elongated with aspect ratio ∼5.2 and mean volume of the order of 10 nm (excluding the silica coating) and spherical with mean volume one order of magnitude larger. These structural features of the nanoparticles together with their aggregation state determine the magnetic anisotropy and the magnetic relaxation processes. In particular, the spherical nanoparticles turn out to be more stable against superparamagnetic relaxation. Mixing the nanoparticles in different proportions allows to modulate the magnetic response of the samples. The two populations of nanoparticles magnetically influence each other through a mean field mechanism, which depends crucially on temperature and rules the hysteretic magnetic properties and their thermal evolution. This magnetic phenomenology has a direct impact on the ability of the mixed samples to generate heat under an alternating magnetic field, a key function in view of nanomedicine applications. Under proper testing conditions, the heating efficiency of the mixed samples is larger compared to that obtained as the sum of those of the parent nanoparticles. This occurs thanks to the mean field produced by the magnetically blocked spherical nanoparticles that stabilizes the thermally fluctuating moments of the elongated ones, which therefore contribute more effectively to the heat production.
调整纳米颗粒的磁性是一项战略目标，旨在以最有效的方式利用它们在纳米医学领域执行特定功能。我们报告了一项系统研究，该研究针对一组通过将不同形状的氧化铁纳米颗粒混合在一起而获得的样品进行：一种是细长的，长径比约为5.2，平均体积约为10纳米（不包括二氧化硅涂层），另一种是球形的，平均体积大一个数量级。纳米颗粒的这些结构特征及其聚集状态决定了磁各向异性和磁弛豫过程。特别是，球形纳米颗粒在抗超顺磁弛豫方面表现得更稳定。以不同比例混合纳米颗粒可以调节样品的磁响应。这两种纳米颗粒群体通过平均场机制相互磁作用，这一机制关键取决于温度，并决定了磁滞特性及其热演化。这种磁现象学直接影响混合样品在交变磁场下产生热量的能力，这是纳米医学应用中的一项关键功能。在适当的测试条件下，混合样品的加热效率比由原始纳米颗粒各自加热效率之和所得到的结果更高。这是由于被磁阻塞的球形纳米颗粒产生的平均场稳定了细长纳米颗粒的热涨落磁矩，因此细长纳米颗粒对产热的贡献更有效。
