Since the introduction (H. Fernández-Morán, Exp. Cell Research 1953), the diamond knife quality has dramatically been improved, leading to a recognition by the biologists community as the ultimate tool for cutting ultrathin TEM sections.
For any of the applications in biology the adeqate diamond knife types were developed.
The introduction of low angle diamond knives led to a reduced compression and a better structure preservation (J. C. Jésior et al., Scanning Microscopy Supplement 3,1989).
The use of an ultrasonic knife led to the best possible structure preservation in rather soft or inhomogenous samples (Studer et al., Journal of Microscopy 1989).
Recently 3D reconstruction of serial ultrathin sectioned gained increasead interest. The problems and best procedure are discussed.
Cryo-ultramicrotomy is used to obtain cryo-sections from cryo-fixed or aldehyde-fixed cryoprotected samples. Freezing, trimming, sectioning, the use of the ionizer, and an improved pick-up solution is presented (E. Bos et al., Journal of Structural Biology 2011). Excellent structure preservation is mandatory for precise localisation of proteins.
Cryo-ultramicrotomy of frozen hydrated samples at 120K gains increasing interest. The sample preparation by high pressure freezing, cryoultramicrotomy, cryo-transfer and cryo-TEM preserve living matter close to the native state (A. Al-Amoudi et al., EMBO J., 2004).
Ultrathin cryosections serve for high resolution imaging and 3D reconstruction (C. E, Hsieh et al., Journal of Structural Biology 2006, A. Al-Amoudi et al., Nature 2007).
A new micromanipulator was developed for pulling the section ribbons and holding the grid (Studer et al., Journal of Structural Biology 2013). The ionizer/charger improves the gliding of the cryo-sections (M. Michel et al., Journal of Microscopy 1992), and fixes cryo-sections on the carbon film of the grid (J. Pierson et al., Journal of Structural Biology 2010).
Ultramicrotomy is the ultimate preparation method for polymers which shall be investigated in the TEM, SEM or in the AFM. Polymer samples are microtomed at room- or at cryo temperatures, according to their glass transition temperature.
Using an oscillating knife allows compression reduction and improved structure preservation in fairly rigid polymers (J. S. Vastenhout et al., Microscopy Today 2006, J. S. Vastenhout et al., Microscopy and Microanalysis 2002). Ultramicrotomy of polymers may be performed on a dry diamond knife, or with a liquid such as a dimethyl-sulfoxide/water mixture (50/50%).
Polymers are stained with OsO4 or RuO4 vapors for showing contrast in the TEM.
For the ultrathin sectioning of metals very small sample blocks (width <50µm) are trimmed. Some metals affect diamond chemically, leading to a fast worn out of the cutting edge. Ultramicrotomy serves for generating high quality metal surfaces for SEM/EBSD investigation (A. M. Sandu et al., Philosophical Magazine 2010).
Ultramicrotomy of brittle Materials Research samples is an alternative to the established preparation technique such as polishing, focused ion beam cutting (FIB), ion thinning, cleavage or others.
Brittle material samples are embedded prior to ultramicrotomy in a rigid epoxi resin (P. Swab et al., MRS Symposium Proceedings 1987). For sectioning hard samples such as ceramics, semiconductors, oxides, crystals, etc, a cross section must be small.(<20µm).
Most brittle materials may be sectioned with 35° diamond knives.