University of Arizona Core Facilities Highlights: Imaging Cores – Electron
What do you get when you combine an electron gun, a vacuum chamber, a series of electromagnetic lenses, and a biological sample? A look into a whole new world.
Paula M. Tonino, ICEL Manager, loading a sample in the single-tilt specimen holder for imaging
Credit: Taylor Edwards, University of Arizona
At the University of Arizona’s Imaging Cores – Electron, or ICEL, facility, researchers use the power of transmission electron microscopy, or TEM, to examine and map biological structures at nanoscale dimensions, revealing details that would otherwise remain unseen.
Paula M. Tonino, ICEL Manager, next to the TEM in the ICEL core facility
Taylor Edwards, University of Arizona
“It’s easy to get immersed in that new world,” Paula M. Tonino, TEM Scientist and ICEL Manager, said. “Every amazing detail revealed is fascinating, and the imaging process always makes me think in new ways.”
ICEL, an Office of Research and Partnerships core facility located in the Life Sciences North building, is the only full-service core offering advanced TEM expertise for a wide variety of basic life sciences and translational research including investigations in cell biology, chemistry, biochemistry, medicine and pharmacology. Also open to external researchers and private industry, ICEL provides end-to-end research services, including experimental design consultation, sample preparation, imaging, data analysis and training.
Tonino and Lyandra Rodriguez, ICEL's Research Technician, Electron Microscopy, receive previously chemically fixed biospecimens and transform them into high-resolution, two-dimensional images with exceptional morphology and cell structural detail (spanning from cell organelles to macromolecular complexes, microorganisms and nanomaterials), at sub-nanometer scales up to 0.36 nm point-to-point resolution and 0.2 nm crystal lattice resolution.
An optical imaging microscope uses a beam of photons. With a transmission electron microscope, an electron gun shoots a high-energy beam of electrons inside a vacuum chamber with electromagnetic lenses, which then focus the beam before it travels through the biological sample, typically thinner than 100 nanometers. After passing through the sample, additional lenses create the visual magnified image for the researcher.
Even as equipment manufacturers make advances in TEM technology, the process of preparing the samples remains the key element controlled by the researchers themselves.
Lyandra Rodriguez, ICEL Technician EM, sectioning a biospecimen for TEM
Taylor Edwards, University of Arizona
“Preparing the biological sample is one of the most important parts of the process to get a high-quality image and depends on the nature of the sample, the type of microscope to be used, and the techniques (e.g., conventional TEM, immuno-EM or negative staining) adapted to the specific project needs and scientific question of the researcher,” Tonino said.
Before the sample arrives at ICEL, researchers must first fix the biospecimen so it doesn’t degrade. Once at ICEL, the next steps in the process involve dehydration to remove all water molecules that would interfere with the electron beam, and infiltration with the addition of reagents, followed by the embedding of the sample into a small, polymerized resin block. After this point, the resin block is sectioned in an ultramicrotome using a diamond knife to obtain a 3 mm diameter grid ultra-thin sections 60 – 90 nm thick, which are then stained by heavy metals to enhance image contrast.
In the ICEL facility, Rodriguez, among many other tasks, oversees the block trimming and sectioning process. “I’ve learned that there’s no such thing as a quick turnaround in high-quality sample preparation,” Rodriguez said.
TEM image of mouse cortical pyramidal neuron
Paula M. Tonino, University of Arizona
“For researchers who come in with a biological sample one day and ask if they can get the images the next day, the answer is no,” Tonino says, emphasizing that “sample preparation takes time and must be done with precision, to preserve its structural integrity, and optimize further imaging results for data analysis.”
In practice, biospecimen preparation is one of the most important parts of the process, and Tonino provides one-on-one training for both sample sectioning and TEM operation so researchers can use the core facility independently.
Another important part of the process is the pre-imaging consultation.
“Before a project begins,” Tonino said, “I need to approach the research question and goals so that we can help determine the right tools and techniques. Whether working with a graduate student, research staff or PI, it’s always a combination of consultation, experimental design and training.”
For her, this support to research projects and collaboration in publications or grants might be the favorite part of working with researchers.
And once a project is complete and images are delivered and data is analyzed, she looks forward to helping researchers plan the next exploration of the world at the nanoscale.