Electron tomography has become a commonly used tool to investigate the three-dimensional (3D) structure of nanomaterials, including colloidal nanoparticle assemblies. However, the nature of the electron microscopy technique typically requires such characterization to be carried out under high vacuum. Therefore, pre-treatment sample preparation is needed for assemblies prepared by (wet) colloid chemistry methods, including solvent evaporation and deposition on a solid substrate (TEM grid). As a result, changes are consistently imposed on the actual nanoparticle organization, which is largely responsible for the nanomaterial properties. Therefore, we propose herein the application of (fast) electron tomography of nanoparticle assemblies while in their original colloidal environment. To address the challenges related to electron tomography in liquid, we devised a method that combines fast data acquisition in a commercial liquid in situ TEM cell with a dedicated reconstruction workflow. We present the application of this method to two different systems, which exemplify the effects of drying and vacuum, depending on the nature of the protecting ligands. 3D reconstructions of assemblies comprising polystyrene-capped Au nanoparticles encapsulated in polymeric shells revealed less compact and more distorted configurations for experiments performed in a liquid medium compared to their dried counterparts. On the other hand, quantitative analysis of the interparticle distance of self-assembled Au nanorods in water agrees with the previously reported dimensions of the ligand layers surrounding the nanorods, whereas the nanorods are in much closer contact in similar dried assemblies. This study, therefore, emphasizes the importance of developing high-resolution characterization tools that preserve the native environment of colloidal nanostructures.

翻译：电子断层扫描已成为研究纳米材料（包括胶体纳米颗粒组装体）三维结构的常用工具。然而，电子显微术的特性通常要求在高真空条件下进行此类表征。因此，对于通过（湿法）胶体化学方法制备的组装体，需要进行预处理样品制备，包括溶剂蒸发和沉积在固体基底（透射电镜网格）上。这一过程不可避免地会改变纳米颗粒的实际组织，而该组织在很大程度上决定了纳米材料的性质。为此，我们在此提出在原始胶体环境中对纳米颗粒组装体应用（快速）电子断层扫描的方法。为应对液相电子断层扫描的挑战，我们开发了一种结合商用原位液相透射电镜池快速数据采集与专用重建工作流程的方法。我们将该方法应用于两种不同体系，这些体系展示了干燥和真空效应（取决于保护配体的性质）。对于包裹在聚合物壳层中的聚苯乙烯封端金纳米颗粒组装体，其三维重建显示，与干燥样品相比，在液相介质中进行的实验呈现出更松散且更扭曲的构型。另一方面，对水中自组装金纳米棒颗粒间距离的定量分析与先前报道的纳米棒周围配体层尺寸一致，而类似的干燥组装体中纳米棒则接触更为紧密。因此，本研究强调了开发能够保留胶体纳米结构原始环境的高分辨率表征工具的重要性。