Cryo-electron microscopy (cryoEM) offers a powerful way to visualize a variety of nanoscale particles and supramolecular assemblies. The cryoEM approach involves flash freezing a sample in a cryogen to preserve nanoparticles in an amorphous frozen layer of water or solvent. Imaging in a transmission electron microscope is performed with a low dose of electrons to avoid destruction of the frozen sample. CryoEM images of gas-filled nanobubbles can provide information on morphological features before and after destruction with high intensity ultrasound. Fourier transforms of cryoEM images can reveal the presence or absence of crystalline order in supramolecular assemblies. CryoEM images will be presented of nanoscale lipid and polymer-stabilized perfluorocarbon gas bubbles with potential for drug delivery, and supramolecular assemblies formed by plant viruses with charged polymeric dendrimers being designed for applications in photon management.<br/><br/>When a cryoEM specimen has a homogeneous structure, 3D single particle reconstruction can be performed. This involves averaging 2D projection images of different particles to generate a 3D structure. A cryoEM reconstruction will be presented of a virus-like particle−polymer conjugate. The 3D structure shows the general conformation of water-soluble polynorbornene polymeric chains attached to a viral capsid. The extent of the interaction between the polymer and the capsid is revealed, providing insight into the shielding properties of the polymer from capsid-specific antibodies. When a cryoEM specimen is heterogeneous, cryo-electron tomography (cryoET) provides an alternate way to generate a 3D structure. This involves collection of a tilt-series of 2D projection images for a defined sample area and generation of a 3D tomogram. Examples will be presented illustrating the application of cryoET to binary mixed polymer brush-grafted silica nanoparticles in aqueous and organic solvents; elongated plant virus-based nanoparticles for enhanced delivery of thrombolytic therapies; and serum albumin-camouflaged tobacco mosaic virus nanoparticles.

Cryo-electron microscopy: 2D and 3D visualization of nanobubbles, nanoparticles, and supramolecular assemblies

256th National Meeting (2018)

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