New approach to electron microscopy imaging of gel nanocomposites in situ

Characterization of Au-nanocomposites is routinely done with scattering techniques where the structure and ordering of nanoparticles can be analyzed. Imaging of Poloxamer gel-based Au-nanocomposites is usually limited to cryo-TEM imaging of cryo-microtomed thin sections of the specimen. While this approach is applicable for imaging of the individual nanoparticles and gauging their size distribution, it requires altering the state of the specimen and is prone to artifacts associated with preparation protocols. Use of Scanning Transmission Electron Microscopy (S/TEM) with fluid cell in situ provides an opportunity to analysis of these complex materials in their hydrated state with nanometer resolution, yet dispensing dense gel-based samples onto electron-transparent substrates remains challenging. We show that Poloxamer gel-based Au nanocomposites exhibiting thermoreversible behavior can be imaged in a fully hydrated state using a commercially available fluid cell holder, and we describe a specimen preparation method for depositing femtoliter amounts of gel-based nanocomposites directly onto the 50 nm-thick SiN window membranes. Ultimately, fluid cell S/TEM in situ imaging approach offers a pathway to visualization of individual nanoparticles within a thick gel media while maintaining the hydrated state of the carrier polymeric matrix.