Electron tomography has become a commonly used tool to investigate the three-dimensional (3D) structure of nanomaterials, including colloidal nanoparticle assemblies. However, electron microscopy is typically carried out under high vacuum conditions. Therefore, pre-treatment sample preparation is needed for assemblies obtained by (wet) colloid chemistry methods, including solvent evaporation and deposition on a solid TEM support. As a result of this procedure, changes are consistently imposed on the actual nanoparticle organization. Therefore, we propose herein the application of electron tomography of nanoparticle assemblies while in their original colloidal liquid environment. To address the challenges related to electron tomography in liquid, we devised a method that combines fast data acquisition in a commercial liquid-TEM cell, with a dedicated alignment and reconstruction workflow. We present the application of this method to two different systems, which exemplify the difference between conventional and liquid tomography, 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 surface-to-surface distance of self-assembled Au nanorods in water agrees with previously reported dimensions of the ligand layers surrounding the nanorods, which are in much closer contact when in similar but dried assemblies. This study, therefore, emphasizes the importance of developing high-resolution characterization tools that preserve the native environment of colloidal nanostructures.

翻译：电子断层成像已成为研究纳米材料（包括胶体纳米粒子组装体）三维结构的常用工具。然而，电子显微镜通常在高真空条件下运行。因此，对于通过（湿法）胶体化学方法获得的组装体，需要进行预处理样品制备，包括溶剂蒸发和沉积在固体透射电镜支撑膜上。这一过程不可避免地改变了纳米粒子的实际组织方式。为此，本文提出在胶体原始液态环境中对纳米粒子组装体进行电子断层成像。为应对液态环境中电子断层成像的挑战，我们设计了一种方法，该方法结合了商用液态透射电镜池中的快速数据采集，以及专用的对准与重构流程。我们将该方法应用于两个不同体系，展示了常规与液态断层成像的差异，具体取决于保护配体的性质。对包裹在聚合物壳层中的聚苯乙烯包覆金纳米粒子组装体的三维重构显示，与干燥样品相比，在液态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表面间距的定量分析，与先前报道的纳米棒周围配体层尺寸一致；而在类似但干燥的组装体中，这些配体层的接触更为紧密。因此，本研究强调了开发能保持胶体纳米结构原始环境的高分辨率表征工具的重要性。