Cryo-Electon Microscopy

Coming summer 2017 !!!

1. Titan Krios G2 300kV Cryo-Electron Microscope

The FEI Titan Krios G2 300kV Cryo-Transmission Electron Microscope is the premier cryo-TEM that is available for both single particle averaging and 3D tomography of vitrified samples. Equipped with a high-brightness field emission gun (X-FEG) and a high-stability 300kV high-tension (HT) generator, the system easily facilitates the high-resolution, sub-nanometer scale imaging of frozen biological specimens. The electron optical column is equipped with ConstantPower™ lenses, which have optimized magnetic circuitry designed to reduce cross talk and keep beam hysteresis to a minimum. This platform is also equipped with an image corrector that removes the increased spherical aberration present due to the larger pole-piece gap of the C-TWIN objective lens, which is required to accommodate large angle specimen tilts in tomographic data acquisition. In addition, the system is equipped with a unique, one-of-a-kind cryogenically cooled sample handling and auto-loading system. The Titan Krios G2 platform has been configured with two detection cameras, a scintillated CMOS camera (FEI Ceta), which will be used for regular TEM/STEM imaging and diffraction applications and an energy-filtered Direct Electron Detection camera (Gatan K2 Summit on a GIF energy filter) for the low dose imaging of frozen biological specimens. In addition, the platform is equipped with two other capabilities, phase contrast imaging and STEM imaging. The phase contrast system almost entirely removes the necessity to acquire images of low contrast objects under beam defocus conditions. Finally, the STEM imaging functionality is essential in high-resolution studies of cellular macromolecules in situ.

System configuration:

  • Sample Auto-loading System - allows twelve independent samples to be loaded into a cassette, which can be transferred into the auto-loading system for delivery into the Titan Krios for imaging. The auto-loader is maintained at liquid nitrogen temperatures to protect the samples from any environmental factors, and each individual sample holder (AutoGrid) is robust and protects the sample against deformation and / or damage.
  • Ceta CMOS camera - The Ceta is a 16 Megapixel digital camera designed specifically for regular TEM/STEM imaging. The large field of view and small pixel size (a characteristic of CMOS sensors) allows a fast read-out for dynamic experiments and is capable, of recording full-frame 4k x 4k images at 30 fps and a reduced field of 512 x 512 at > 250 fps. The camera can also easily switch between this fast mode and high-resolution mode with ease.
  • Gatan K2 Summit Direct Electron Detector with GIF Energy Filter - The combined Gatan K2 Summit Direct Electron Detection camera and GIF energy filter – the “BioQuantum 967” allows for the direct detection of electrons at high sensitivity. In addition, the presence of the GIF energy filter allows the preferential detection of zero-loss electrons, thus serving as an additional mechanism to enhance the contrast of unstained, vitrified biological specimens.
  • Cs Aberation Corrector - The C-TWIN objective lens with its larger pole-piece gap is essential for high tilt angle tomographic acquisitions. Its symmetric design allows for the changing of the accelerating voltage without adjusting the stage z-position. Additionally, it ensures that there is no performance compromise, or any re-alignment between TEM and STEM imaging modes. However, whilst important for tomography, the larger pole-piece gap in the C-TWIN objective lens increases spherical aberration. The addition of an image corrector removes this added spherical aberration (Cs) thus restoring the TEM/STEM resolution to that of a Titan microscope platform with a smaller pole-piece separation.
  • Volta Phase Contrast System - A major issue in the imaging of unstained, vitrified samples is the lack of electron density, and thus contrast in the acquired images. A new, and cutting-edge approach that almost entirely removes the need for the addition of beam defocus is phase contrast imaging. By separating the phases of elastically and inelastically scattered electrons that pass through the sample by 90o, the in-focus contrast in the imaging plane can be drastically improved, which is beneficial in the imaging of weak phase objects, such as vitrified biological specimens.
  • STEM detector - The ability to scan the electron beam whilst acquiring the transmitted electron signal, a so-called “STEM” image is essential in high-resolution studies of cellular macromolecules. The incorporation of STEM functionality onto the Titan Krios G2 platform increases its versatility without compromising any of the other imaging modes of the microscope (TEM, EFTEM etc).