Roca Alejandro G, Veintemillas-Verdaguer Sabino, Port Marc, Robic Caroline, Serna Carlos J, Morales Maria P
Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, 28049 Madrid, Spain.
J Phys Chem B. 2009 May 14;113(19):7033-9. doi: 10.1021/jp807820s.
Colloidal dispersions of monodispersed and high-crystalline magnetite nanoparticles have been used to establish a relationship between magnetic properties and magnetic resonance (MR) relaxometric parameters in vitro. Magnetite nanoparticles with diameters between 4 and 14 nm were synthesized by thermal decomposition of Fe(acac)3 in different organic solvents and transformed to hydrophilic by changing oleic acid for dimercaptosuccinic acid (DMSA). A final treatment in alkaline water was critical to make the suspension stable at pH 7 with xi-potential values of -45 mV and hydrodynamic sizes as low as 50 nm. Samples showed superparamagnetic behavior at room temperature, which is an important parameter for biomedical applications. Susceptibility increased with both particle and aggregate size, and for particles larger than 9 nm, the aggregate size was the key factor controlling the susceptibility. Relaxivity values followed the same trend as the suspension susceptibilities, indicating that the aggregate size is an important factor above a certain particle size governing the proton relaxation times. The highest relaxivity value, r2=317 s(-1) mM(-1), much higher than those for commercial contrast agents with similar hydrodynamic size, was obtained for a suspension consisting of 9 nm particles and 70 nm of hydrodynamic size, and it was assigned to the higher particle crystallinity in comparison to particles prepared by coprecipitation. Therefore, it can be concluded that in addition to the sample crystallinity, both particle size and aggregate size should be considered in order to explain the magnetic and relaxivity values of a suspension.
单分散且高结晶的磁铁矿纳米颗粒的胶体分散体已被用于在体外建立磁性能与磁共振（MR）弛豫测量参数之间的关系。通过在不同有机溶剂中热分解Fe(acac)3合成了直径在4至14纳米之间的磁铁矿纳米颗粒，并通过将油酸换成二巯基琥珀酸（DMSA）使其变为亲水性。在碱性水中进行的最终处理对于使悬浮液在pH值为7时稳定至关重要，其ζ电位值为-45 mV，流体动力学尺寸低至50纳米。样品在室温下表现出超顺磁性行为，这是生物医学应用的一个重要参数。磁化率随颗粒和聚集体尺寸的增加而增加，对于大于9纳米的颗粒，聚集体尺寸是控制磁化率的关键因素。弛豫率值与悬浮液磁化率遵循相同趋势，表明聚集体尺寸是在一定颗粒尺寸以上控制质子弛豫时间的重要因素。对于由9纳米颗粒和70纳米流体动力学尺寸组成的悬浮液，获得了最高弛豫率值r2 = 317 s(-1) mM(-1)，远高于具有相似流体动力学尺寸的商业造影剂，这归因于与通过共沉淀制备的颗粒相比更高的颗粒结晶度。因此，可以得出结论，为了解释悬浮液的磁性能和弛豫率值，除了样品结晶度外，还应考虑颗粒尺寸和聚集体尺寸。
