固定法

fixation methods

SEMで生物試料を観察するために、細胞や生体から摘出した組織などを生きた状態に近い形態に保持する手法。生物試料の固定法は、タンパク質や脂質等を薬品で化学的に固定する方法と、組織や細胞内の水分を凍結して物理的に固定する方法の2つに大別される。
化学固定に広く用いられているのは、細胞や組織を直接固定液に浸漬する浸漬固定である。その他に、動物の場合には血管系を介して固定液を注入して固定する灌流固定、カビの場合には試料を固定液の蒸気に曝すことで固定する蒸気固定などがある。
物理固定に広く用いられるのは、組織を液体窒素、液体エタンなどに直接浸漬して凍結する浸漬法である。その他に、液体窒素、液体ヘリウムなどで冷却した金属に組織を圧着し凍結する金属圧着法、凍結時に高圧をかけて液体窒素で凍結する高圧凍結法がある。

Methods to preserve the morphological structure of biological specimens such as cells and tissues extracted from living organisms, by keeping them close to their living states for scanning electron microscope (SEM) observation.
The fixation methods are classified into chemical fixation and physical fixation. The former method chemically fixes proteins, lipids, etc., by using chemicals and the latter method physically fixes water in cells or tissues by freezing them.
For chemical fixation, immersion fixation is widely used, in which cells or tissues are directly immersed into a fixation solution. In addition, two other methods are often used: One is perfusion fixation used for animals, in which a fixation solution is injected into a specimen through the vascular system. Another is vapor fixation used for mold, in which the specimen is exposed to the vapor of a fixation solution.
For physical fixation, immersion freezing is widely used, in which tissues are directly immersed into liquid nitrogen or liquid ethane. In addition, two methods are often used: One is metal mirror freezing (slam freezing), in which a tissue is punched against a metal block cooled by liquid nitrogen or liquid helium. Another is high-pressure freezing, in which a tissue is frozen at the liquid nitrogen temperature while high pressure is applied.