What kinds of materials can be imaged under in-situ liquid exposure?
Alejandra Londono-Calderon, Tanya Prozorov, and their colleagues at AMES Lab and Iowa State University published on their use of the Hummingbird Scientific Gen IV in-situ SEM liquid flow sample holder to image Poloxamer gel-based Au nanocomposites in their hydrated state. Liquid-phase electron microscopy provided an alternative pathway to cryoEM for imaging these beam-sensitive nanocomposites. In-situ scanning electron microscopy (SEM) characterization was performed alongside in-situ scanning transmission electron microscopy (S/TEM) and bright-field cryo-TEM for comparison across imaging techniques.
Bright-field TEM images of nanoparticles suspended in gel. a) Ready Au-PEG functionalized nanoparticles (NP) to be mixed with F127 Poloxamer gel, and b) the nanoparticles extracted from the F127 Poloxamer citrate-bearing gel formed by the in situ reduction of HAuCl4. c) Schematic of the front-loaded Surface Patterning Tool (SPT) used to print micro-droplet of polymer to a SiN membrane and the enclosed cell. d) HAADF STEM image collected at 20kV and 6.3 pA of the fluid cell showing Au nanoparticles. e) Signal-to-Noise ratio analysis of 10 nanoparticles yields a value of 8.7±1.1, above Rose criterion of SNR=5 for visible nanoparticles. Copyright © 2019 Elsevier Ltd. All rights reserved.
The nanocomposite exhibits thermoreversible gelation, remaining a liquid during printing onto the sample substrate with a cooling stage, but setting into a gel upon warming to room temperature. Using the liquid SEM sample holder, the ~5 nm gold nanoparticles were successfully detected in a ~500 nm thick polymeric gel layer. Using the in-situ liquid flow SEM sample holder, the team demonstrated this novel approach to imaging of gel-based nanocomposites, expanding options for structural characterization and informing future improvements to templated synthesis and assembly of mesoporous materials and other nanocomposites.
Reference: Alejandra Londono-Calderon, Srikanth Nayak, Curtis L. Mosher, Surya K. Mallapragada, and Tanya Prozorov, Micron 120 (2019) DOI: 10.1016/j.micron.2019.02.010
Full paper Copyright © 2019 Elsevier Ltd. All rights reserved.
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