Histological analysis services

Histology is the branch of biology that studies tissues using different marking techniques: staining, use of antibodies or nucleic acid probes. It is widely used in the diagnosis of abnormal cells and in understanding the distribution of markers in cells.

On Labtoo histological analyses include tissue cutting, sample preparation, marking, and imaging.

Histological section

A histological section is a slice of an organ thin enough to be observed under a microscope. They are made by a microtome or an ultramicrotome depending on the thickness. The fabrics are embedded in epoxy resins or paraffin. The cuts can be made without prior inclusion, and are then frozen and made by a cryomicrotome.

Before cutting, a fixation followed by an inclusion must be made. The purpose of inclusion is to allow fine and regular cuts to be made. The most commonly used inclusion medium is paraffin.

Sample preparation and marking

Samples of histological section The sample preparation includes a colouring step. As the dyes are in aqueous solution, the cuts must first be rehydrated. This is then carried out after dewaxing the sections (by heat and toluene baths) by immersing the slides in alcohol baths of decreasing degree and then in distilled water. The purpose of colourings is to accentuate contrasts in order to better recognize the different elements of the preparation.

Routine staining uses one or two different dyes: hematéine or hematéine-eosine (H.E.). Hematéine colours the nuclei in purple and eosin colours the cytoplasms in pink.

The coloured sections are then mounted between the blade and the lamella with a synthetic resin whose refractive index is similar to that of glass. The slides are ready to be observed under an optical microscope to obtain the results of the cuts for analysis.

Histological observation with an electron microscope (EM)

If you want to make an observation with the Electron Microscope, the protocol is different. Although the steps are the same, the reagents used are not similar. Indeed, the fixation is done in buffered glutaraldehyde and is followed by a post-fixing with osmic acid.

The inclusion is made in a synthetic resin such as Epon or Araldite, after dehydration of the fragments in alcohols and propylene oxide.

The cuts are made thanks to an ultra-microtome that allows ultra-fine cuts of about 80 nm thick to be obtained. These are collected on copper grids. With the same ultramicrotome, semi-fine sections can be made, observable in MO and used to guide the choice of areas to be studied in ME.

The contrast of the cuts is made with uranyl acetate and lead salts such as lead citrate.

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