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Electron Microscopy

The Electron Microscope Suite is located on Level 5 of the Miall Building. It comprises five transmission (TEM) microscopes (FEI Tecnai F20, Philips CM10 (2) and Jeol 1200ex (2)) and one scanning (SEM) microscope (Camscan Series III). There is also a wide variety of ancillary equipment (coating units, ultramicrotomes, optical diffractometer, ultra-rapid freezing apparatus (including time-resolved) etc).

FEI Tecnai G2 F20 field emission gun (FEG) electron microscope  

New FEG microscope installed.

The new FEI Tecnai G2 F20 field emission gun (FEG) electron microscope was recently commissioned and is now collecting data. The highly coherent FEG electron source is especially suited for phase contrast imaging unstained, frozen-hydrated specimens. This microscope is fitted with the Gatan Ultrascan 4000 CCD camera (4k x 4k pixels), which is one of the first of its type and allows direct recording of digital data.

New Electron Energy Filter Installed

The Tecnai F20 microscope has also recently been fitted with a Gatan GIF electron energy, which allows images to be formed from electrons with selected energy. It is mainly planned to use the filter to remove inelastically scattered electrons that have lost energy and thereby form 'zero-loss' images. This can improve image quality from thick hydrated specimens. Such specimens give a high proportion of inelastic scattering, which results in blurring of images because these electrons have slightly increased wavelength. Energy filtering is especially useful in obtaining tilted images of intact cells for tomographic 3D reconstruction. The energy filter was funded by a BBSRC REI grant that also included a new ultra high tilt cryo-specimen holder (Gatan 914) and software for automated tilt series acquisition.

Phillips CM10 microscope Jeol 1200ex microscope
Phillips CM10 microscope Jeol 1200ex microscope

Work undertaken ranges from relatively conventional procedures such as resin embedding, metal shadowing and negative staining to development and application of new microscopy methods. In recent years there has been a renaissance in biological electron microscopy. This has largely been based on increased use of unstained specimens, especially frozen and hydrated. To this end, two of our TEMs have cold specimen holders capable of working at ~-170 degC. The ultra-fast freezing (~10 million deg C/sec) can also be used to trap key reaction intermediates with millisecond time-resolution.

Much recent progress has also resulted from developments in digital image processing. This allows 3-dimensional models to be produced by combining different views of an object. It can also lead to improved resolution by combining images (perhaps many thousands) from weakly irradiated specimens where the electron beam damage limits information recovery. One type of image processing mainly relies on diffraction of 2-dimensional crystals as means to combine the data. Another involves so-called single particle processing applied to separate objects.


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