Transmission Electron Microscope
The transmission electron microscope uses a high energy beam of electrons to visualise both thin sections of biological and suitable materials specimens and very small whole objects (bacteria, chromosomes and nanocrystals). It is possible to obtain high resolution data of detailed intracellular structures and small particles at magnifications up to 250,000x. TEM can be combined with many procedures such as X-Ray microanalysis and electron diffraction for materials samples and immunology and in situ hybridisation to provide information about cellular processes.
The Philips CM 12 TEM has a microprocessor-based control system, and can operate at various accelerating voltages (20, 40, 60, 80, 100 and 120 kV), depending on the sample and technique used. The resulting image can be displayed, captured and saved via a digital camera onto a pc. The microscope has a cool beam gun which causes less damage to the specimen.
- The sample/grid holder is mounted in a side-entry motorised goniometer stage, which can tilt from -60˚ to +60˚ and can be used to provide a stereo-pair image of the sample.
- The resolution which can be attained is specimen dependant, varying from 1.4Å (for lattices) to 4Å for point to point measurements.Standard magnifications of 1,000 times to 250,000 times are obtained in 14 steps and there is also a low magnification mode providing 100 times to 800 times.
- Electron diffraction (third image below) is possible with the field-limiting aperture for whole field or selected areas (minimum field of view 0.2μm).
- An iXRF system provides elemental analysis spectra and quantitation of suitable samples
The Main Unique Aspects Of The Technique
- The TEM remains the principal instrument to provide high resolution ultrastructural information from the internal regions of cells (animal or plant) and bacteria, particularly where samples must be scanned for the smallest detail.
- By use of various fixation protocols, combined with immunocytochemistry, histocytochemistry, autoradiography and genetic hybridisation techniques, cell structures and functions can be localised within either in vitro cell layers and cell/biomaterial constructs or biopsy tissues.
- The elemental composition of cellular inclusions and small particles are possible using TEM and X-Ray analysis. This can provide data on elemental localisation atmicro and nanoscale not possiblewith many other techniques.
Examples Of Work Undertaken At The Institute
The TEM has been important in the progress of research in several clinical departments, particularly Periodontology, Endodontology and for imaging in Microbiology. Plaque, calculus, gingiva and the tooth and root canal have been examined for detailed ultrastructural information, particularly in situ identification using immunocytochemistry (second image) and hybridisation methodologies to identify micro-organisms and cell functions. Whole cell mounts which have been negatively stained are routinely used to establish the presence of bacteriophages (fourth image) and preparations of cell fractions.
As part of detailed information required in biomaterials research, the TEM has been used to examine microcrystals (image one) within foam structures, mineralisation of collagen constructs, novel particles for drug delivery and tissue reconstruction, nanoparticles for antique artifact preservation.