Category : Chemistry, biochemistry, electro-chemistry (laboratory precision equipment, devices and supplies) > Diamond knives

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Thinner sections
No compression
Better structural preservation
For many years Diatome diamond knives have been used successfully for a wide range of room- and low temperature sectioning applications. Major advances in immunocytochemistry, the sectioning of frozen hydrated specimens, semithin sectioning for optical microscopy, as well as the sectioning of hard industrial samples have been realized using Diatome diamond knives (Ref 1, 2, 3, 4). The development of the Static Line II ionizer enabled dry ultramicrotomy of Lowicryls and a considerable improvement in cryosectioning (Ref 5).

Despite these innovations, until now, one major obstacle remained, preventing us from achieving perfect ultrathin sections: "compression" which we define as the shortening of the section compared to the sample height. The amount of compression depends on various factors including:

The wedge angle of the knife.
The hardness of the sample.
The interaction diamond surface / section surface.
The section thickness
The most critical factor is the wedge angle of the knife. It was shown that reducing the wedge angle results in a reduction of compression, hence better preservation of ultrastructure which allows a higher achievable resolution (Ref 6, 7). However, the wedge angle may not be reduced ad infinitum. A further reduction results in a lower cutting edge quality and a considerably shorter life span.

In cryo-ultramicrotomy, compression, expressed as a percentage, was found almost equal to the wedge angle in degrees:

45° knife 40-50%
35° knife 30-40% (Ref 8, 9)
An oscillating knife for low temperature applications is in preparation.

In room temperature ultramicrotomy, we have found the following compression factors (section thickness 50nm):

10-20% for Epon, Araldite, EM-Bed, and other epoxy resins.
12-24% for Lowicryl K4M.
10-17% for Spurr's (hard grade).
8-13% for LR White (hard grade).
These limitations have stimulated our efforts to develop the oscillating knife.

It has been shown that compression in frozen-hydrated sections is the limiting factor for successful electron topographic analysis (Ref 10, 11). Cryo sections from vitrified samples without compression were achieved by A. Al-Amoudi, LAU, University of Lausanne (Ref 12).

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