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Alejandra Londono-Calderon1 Srikanth Nayak2 1 Surya Mallapragada2 1 Tanya Prozorov1

1, U.S. DOE Ames Laboratory, Ames, Iowa, United States
2, Iowa State University, Ames, Iowa, United States

Polymeric gel-based and hydrogel nanocomposite systems are promising materials in nanomedicine, pharmaceutical, and biosensing applications. For example, Pluronic-based Au-nanocomposites have shown to be advantageous theranostic agents for multimodal imaging of carcinoma cells. The rich phase diagram of aqueous solutions of Pluronic block copolymers offers a pathway for a targeted formation and placement of Au nanoparticles and for a controlled ordering of spatial arrangement within the gel matrices of these materials, while the interactions between the individual blocks of the polymer leads to enhanced nanoparticles stability and biocompatibility.
Due to the viscous nature of the Au-Pluronic nanocomposite gels, their characterization is normally limited to Small Angle X-Ray Scattering (SAXS) and Cryo-TEM imaging of cryo-ultramicrotomed thin slices of either a freeze-dried, or a vitrified specimen. While this approach allows viewing the individual nanoparticles and gauging their size distribution, it does not provide sufficient information about spatial arrangement of the nanoparticles within the gel

We present a novel approach to imaging Pluronic-based Au-nanocomposites with the liquid cell in situ. A cold-stage nanoprinting system (Nano eNabler molecular printing) was used to control the deposition of 1-5 um droplets on SiN windows by a microfabricated surface patterning tool (STP) cantilever. The printed SiN windows were assembled for in situ experiments in Hummingbird Scientific Liquid Cell holder and imaging by using a Tecnai G2-F20 Scanning Transmission Electron Microscope operating at 200 kV in HAADF-STEM mode. We demonstrate that in situ liquid cell can be used for direct imaging of nanoparticles in viscous media and at various stages of drying, offering important clues to understanding how the nanoparticles are arranged in polymeric matrices. We also discuss specimen deposition protocol and the effects it makes on the imaging.

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