Chemistry Department, The University of York, Heslington, York, YO10 5DD, UK.
Phys Chem Chem Phys. 2011 May 28;13(20):9812-7. doi: 10.1039/c0cp02508a. Epub 2011 Apr 18.
The factors limiting the relaxivity (r) of MRI contrast agents based on small (∼2.0 nm) gold nanoparticles functionalised with paramagnetic chelates were explored using EPR spectroscopy. The EPR analysis suggested that nanoparticle-attached chelates exhibit relatively high tumbling rates which restrict their relaxivity. Two different strategies were employed in order to test this hypothesis and hence improve the relaxivity of the nanoparticle-based contrast agents. In the first approach, the particle diameter was increased. This resulted in lower surface curvature and hence tighter ligand packing, which in turn led to increased relaxivity. In the second approach, the nanoparticles were overcoated with multilayers of oppositely charged polyelectrolytes. The restricted motion of Gd(3+) chelates coated by 2-4 polymer layers led to increased relaxivity which was dramatically reduced for thicker layers, presumably due to restricted diffusion of water molecules.
使用电子顺磁共振（EPR）光谱研究了功能化超小（约 2.0nm）金纳米粒子的顺磁螯合物的 MRI 造影剂的弛豫率（r）的限制因素。EPR 分析表明，纳米粒子附着的螯合物表现出相对较高的旋转率，这限制了它们的弛豫率。为了验证这一假设并提高基于纳米粒子的造影剂的弛豫率，采用了两种不同的策略。在第一种方法中，增加了颗粒直径。这导致较低的表面曲率和更紧密的配体堆积，从而提高了弛豫率。在第二种方法中，纳米粒子用带相反电荷的多聚电解质进行了多层包裹。通过 2-4 层聚合物涂层包裹的 Gd（3+）螯合物的受限运动导致弛豫率增加，而对于更厚的涂层，弛豫率则显著降低，这可能是由于水分子的扩散受限。
