Soft matter and nanomaterials characterization by cryogenic transmission electron microscopy

Soft matter has historically been an unlikely candidate for investigation by electron microscopy techniques due to damage by the electron beam as well as inherent instability under a high vacuum environment. Characterization of soft matter has often relied on ensemble-scattering techniques. The recent development of cryogenic transmission electron microscopy (cryo-TEM) provides the soft matter community with an exciting opportunity to probe the structure of soft materials in real space. Cryo-TEM reduces beam damage and allows for characterization in a native, frozen-hydrated state, providing direct visual representation of soft structure. This article reviews cryo-TEM in soft materials characterization and illustrates how it has provided unique insights not possible by traditional ensemble techniques. Soft matter systems that have benefited from the use of cryo-TEM include biological-based soft nanoparticles (e.g., viruses and conjugates), synthetic polymers, supramolecular materials as well as the organic-inorganic interface of colloidal nanoparticles. Many challenges remain, such as combining structural and chemical analyses; however, the opportunity for soft matter research to leverage newly developed cryo-TEM techniques continues to excite.