Modern Cryogenic-Temperature Electron Microscopy in the Nanostructural Study of Soft Matter
Cryogenic-temperature transmission electron microscopy (cryo-TEM) is now accepted as an almost standard tool in the study of complex liquids, i.e., liquid systems with aggregates or building blocks on the nanometric scale. Methodologies have been developed to capture the nanostructure of liquid systems, while preserving their original state at a given concentration and temperature. Cryo-TEM is now widely used to study synthetic, biological, and medical soft matter. Originally developed for aqueous systems, it has been also applied successfully in the study of non-aqueous systems. Recent developments in TEM include highly-sensitive cameras that allow imaging with very few electrons, thus reducing electron-beam radiation-damage, a main limitation in electron microscopy of soft matter. Recent introduction of the analog to light microscopy “phase-plate”, enhances image-contrast in low-contrast specimens, another major limitation in microscopy of soft matter.
However, cryo-TEM cannot be used to study highly viscous systems, or those containing objects larger than several hundreds of nanometers. Recent developments in high-resolution scanning electron microscopy (HR-SEM) have made it an ideal tool for the study of nano-aggregates in viscous systems or in systems containing large objects hundreds of nanometers and larger, in which small (nanometric) features are to be imaged. Improved field-emission electron guns, electron optics and detectors have made it possible to image nanoparticles down to a few nanometers. Liquid nanostructured systems can now be studied by cryo-SEM, using much-improved cryogenic specimen holders and transfer systems. In recent years we have developed and improved a novel specimen preparation methodology for cryo-SEM specimens that preserves the original nanostructure of labile complex liquids, at specified composition and temperature, quite similarly to what had been done in cryo-TEM.
In my talk I will describe the state-of-the-technology of cryo-TEM and cryo-SEM, and demonstrate the application of our combined methodology in nano- and biotechnology. Among others, I will describe applications in the study of polyelectrolytes and their interaction with oppositely-charged amphiphiles, biological system, such as extracellular vesicles, and carbon nanotubes dispersed in super-acids.