Electron microscopy of therapeutic and diagnostic nanoparticles

我们已经分析了生物纳米颗粒，这些生物纳米颗粒被设计用于标记细胞，然后通过体内磁共振成像在动物模型中对这些细胞进行成像。 这些纳米复合物包含三种FDA批准的药物（肝素，鱼精蛋白和ferumoxytol），可以被人体细胞系吸收，并在植入啮齿动物时被检测到。 ferumoxytol组分的主要成分是超顺磁性氧化铁纳米颗粒（SPIONP），其为诊断成像提供MRI对比。 我们已经进行了电子断层扫描和能量过滤透射电子显微镜（EFTEM），以确定使用元素特异性信号的三种成分在单个纳米复合物内的分布。 鱼精蛋白组分用氮信号成像，肝素组分用硫信号成像，并且ferumoxytol的周围壳用铁信号成像。 电子断层扫描也被用来可视化的三维组织的ferumoxytol纳米颗粒内的约200 nm直径的纳米复合物。我们的分析表明，纳米复合物含有由大约1：1质量比的鱼精蛋白和肝素组成的均匀软核，这与鱼精蛋白上的正电荷与肝素上的负电荷的平衡一致。 电子显微镜使我们能够表征另一种SPIONP，该SPIONP与纳米药物制剂相结合，该纳米药物制剂由抗癌药物阿霉素加载到氧化铁纳米颗粒上的聚乙烯亚胺涂层中，形成治疗诊断纳米复合物。 磁性纳米晶体如SPIONP主要被开发为MRI造影剂和用于跟踪干细胞的磁性标签。 然而，通过这种设计，SPIONP可以作为药物递送载体到达肿瘤部位，并通过磁对比对这些部位进行成像。 我们还表征了通过用聚天冬氨酸涂覆而溶解的单分散氧化锰纳米颗粒。 这些颗粒在MRI中显示出更高的R1弛豫率，因为聚天冬氨酸层比其他更常用的涂层（如PEG化磷脂）更具亲水性和致密性，这有助于更有效的水-锰相互作用。特别是，核尺寸为10 nm的纳米颗粒在MRI对比度方面比核尺寸较大的纳米颗粒表现出更大的增强。

We have analyzed bionanoparticles that are designed for labeling cells and then imaging those cells in animal models by in vivo magnetic resonance imaging. These nanocomplexes, comprising three FDA-approved drugs (heparin, protamine and ferumoxytol), can be taken up into human cell lines, and detected when implanted into rodents. The major component of the ferumoxytol component is superparamagetic iron oxide nanoparticle (SPIONP), which provides MRI contrast for diagnostic imaging. We have performed electron tomography and energy-filtered transmission electron microscopy (EFTEM) to determine the distribution of the three constituents within the individual nanocomplexes using element-specific signals. The protamine component was imaged with the nitrogen signal, the heparin component with the sulfur signal, and the surrounding shell of ferumoxytol with the iron signal. Electron tomography was also employed to visualize the three-dimensional organization of the ferumoxytol nanoparticles within the approximately 200-nm diameter nanocomplexes. Our analysis showed that the nanocomplexes contained a homogeneous soft core consisting of approximately a 1:1 mass ratio of protamine and heparin, consistent with a balancing of the positive charge on protamine with the negative charge on heparin. Electron microscopy has enabled us to characterize another SPIONP that is combined with a nano-drug formulation consisting of the anti-cancer drug doxorubicin loaded into a polyethyleneimine-coating on the iron oxide nanoparticles, forming a theranostic nanocomplex. Magnetic nanocrystals like SPIONPs have been developed mainly as MRI contrast agents and as magnetic labels for tracking stem cells. However, with this design, the SPIONPs can function as drug delivery vehicles to reach tumor sites and image those sites through magnetic contrast. We have also characterized monodisperse manganese oxide nanoparticles that had been solubilized by coating with polyaspartic acid. These particles show much higher R1 relaxivity in MRI because the polyaspartic acid layer is more hydrophilic and compact than other more commonly used coatings such as PEGylated phospholipid, which facilitates more efficient water-manganese interactions. In particular, nanoparticles with a core size of 10 nm exhibited greater enhancement in MRI contrast than did ones with larger core sizes.