Electron microscopy—both scanning (SEM) and transmission (TEM)—can be used by an increasing number of life scientists. To explore the new technologies in this realm of imaging, this article talks with experts from Carl Zeiss, FEI, and JEOL.
“Electron microscopy is perceived to be a technology that is pretty complicated, and where you need a high skill set to operate the system, but that has changed and also clearly depends on the type of instrument,” says Thomas Wohlfarth, director of marketing for the life sciences business unit at FEI. “We make our applications more accessible by developing tools which are easier to operate and by dedicated workflows [that] our tools are fully embedded in.” In fact, that makes up a trend for SEM and TEM. Vern Robertson, SEM technical sales manager at JEOL, adds: “Automation allows users with less training to use SEM and TEM. But you also need an interface that the average user feels comfortable with.”
Using workflow solutions
Making electron microscopy easy to use depends on the workflow. For TEMs from FEI, Wohlfarth says, “We deliver a purpose-built workflow for proteins and protein complexes, even adding dynamic information to the 3D structure of proteins and protein complexes.” This workflow starts with sample preparation and ends with the reconstruction of a 3D image of the protein. “This is a streamlined, automated and highly focused workflow for structural biologists,” Wohlfarth says.
Advancing the flow in TEM also involves hardware changes. For example, Kevin McIlwrath, TEM applications scientist at JEOL, says, “We’re going to low-dose electron microscopy in biology.” Thus includes JEOL platforms that only require 120 kilovolts, compared to traditional TEM systems that use 200–300. In addition, JEOL soups up TEM with thin film–phase plate technology. “This creates a 1-micron aperture in the column to enhance the concentration of unstained samples,” McIlwrath says. “Combined with our in-column energy filters, this technology provides extremely high contrast for unstained cryo-samples and low-dose tomography.”
Some of the key advances also include the interface. For example, some of JEOL’s newest platforms, such as the 1400-plus TEM, include touch screens. The 1400-plus also includes JEOL’s phase plates and energy filters, which McIlwrath says, let “you see details that you wouldn’t with other systems.”
With SEM, some companies make systems for beginners. As Robertson says, “Our new JEOL 6010LA is an entry-level scope that we’re seeing first-time people use.” He adds, “It’s a new world of SEM that is very affordable, but people are surprised by its features, such as low-vacuum capability.” Even better, the 6010LA comes as a single unit with SEM and energy-dispersive spectroscopy.
Beyond getting simpler, SEM is getting more powerful, especially with field-emission SEM (FE-SEM). As Martin Edelmann, PhD, product manager for FE-SEMs in biosciences at Carl Zeiss, explains: “In the last few years, the FE-SEM’s quality has approached that of TEM.” He adds, “You can now use FE-SEM on typical TEM samples down to a couple nanometers of resolution. Using the Carl Zeiss Gemini technology, FE-SEM images look like TEM in many cases.”
By using FE-SEM instead of TEM, customers get several advantages, according to Edelmann. “SEM is easier to use and easier to image large areas,” he says.
More researchers are also using 3D techniques with SEM. To make this easier, Carl Zeiss includes the 3View in situ ultra microtome from Gatan in its MERLIN and SIGMA platforms.
Rather than using electron microscopy alone, correlative microscopy combines the best of two worlds. For example, FEI’s Tecnai with iCorr combines TEM and fluorescent-light imaging. Wohlfarth adds, “We’ve launched a family of dedicated solutions for our customers, including a full FEI sample-centric workflow which starts with a purpose-built light microscope for correlative microscopy called CorrSight, which links to our SEMs using one software package.”
Other companies take different approaches. For example, Robertson says that JEOL developed a sample holder that can be moved between light and electron microscopes. “We make a bench-top stereomicroscope with 10–30× for transmitted or reflected light imaging, and then you can take the same sample on a holder and plug it into the stage of our SEM.” Then software provides a montage of the two images.
Shuttle & Find from Carl Zeiss allows correlative microscopy within Carl Zeiss’ portfolio. “Holders with calibration marks together with a specific software module make sure that you get correlated light and electron microscopy images of the same area very fast and with high precision” says Edelmann. “You can go from light to electron or the reverse.”
With such tools and the technology behind SEMs and TEMs, many more life scientists can now explore samples at much higher resolution.