Department of Chemistry and Biomolecular Sciences, University of Ottawa, 10 Marie Curie St. Ottawa (ON) K1N 6N5, Canada.
Nanoscale. 2019 Apr 4;11(14):6794-6801. doi: 10.1039/c9nr00241c.
Sodium gadolinium fluoride (NaGdF4) nanoparticles are promising candidates as T1 shortening magnetic resonance imaging (MRI) contrast agents due to the paramagnetic properties of the Gd3+ ion. Effects of size and surface modification of these nanoparticles on proton relaxation times have been widely studied. However, to date, there has been no report on how T1 relaxivity (r1) is affected by the different polymorphs in which NaGdF4 crystallizes: cubic (α) and hexagonal (β). Here, a microwave-assisted thermal decomposition method was developed that grants selective access to NaGdF4 nanoparticles of either phase in the same size range, allowing the influence of host crystallinity on r1 to be investigated. It was found that at 3 T cubic NaGdF4 nanoparticles exhibit larger r1 values than their hexagonal analogues. This result was interpreted based on Solomon-Bloembergen-Morgan theory, suggesting that the inner sphere contribution to r1 is more pronounced for cubic NaGdF4 nanoparticles as compared to their hexagonal counterparts. This holds true irrespective of the chosen surface modification, i.e. small citrate groups or longer chain poly(acrylic acid). Key aspects were found to be a polymorph-induced larger hydrodynamic diameter and the higher magnetization possessed by cubic nanoparticles.
氟化钆钠（NaGdF4）纳米颗粒由于 Gd3+ 离子的顺磁性质，是 T1 缩短磁共振成像（MRI）对比剂的有前途的候选物。这些纳米颗粒的尺寸和表面修饰对质子弛豫时间的影响已得到广泛研究。然而，迄今为止，尚无关于 NaGdF4 结晶时不同多晶型（立方（α）和六方（β））如何影响 T1 弛豫率（r1）的报道。在这里，开发了一种微波辅助热分解方法，该方法可选择性地获得相同尺寸范围内的任意相的 NaGdF4 纳米颗粒，从而可以研究宿主结晶度对 r1 的影响。结果发现，在 3 T 下，立方 NaGdF4 纳米颗粒的 r1 值大于其六方类似物。根据 Solomon-Bloembergen-Morgan 理论对此结果进行了解释，表明与六方相比，立方 NaGdF4 纳米颗粒的内球对 r1 的贡献更为明显。这与所选择的表面修饰无关，即小的柠檬酸基团或更长链的聚丙烯酸。发现关键方面是多晶型诱导的更大水动力直径和立方纳米颗粒所具有的更高磁化强度。
