固定的目的在于保存细胞和组织的原有形态结构，固定剂能阻止内源性溶酶体酶对自身组织和细胞的自溶、抑制细菌和霉菌的生长，固定剂通过凝固、生成添加化合物等使蛋白质内部结构发生改变，从而使酶失活，固定剂对细胞核细胞外成分发生物理改变，固定液主要分为醛类固定液、汞类固定液、醇类固定液、氧化剂类固定液、苦味酸盐类固定液等，较为常用的是醛类中的福尔马林、醇类中的乙醇。
AAF固定液 (适用于成熟组织) 又称 FAA/AFA 固定液 (70%)，又称万能固定剂，主要由 70% 乙醇 (A)、5% 乙酸 (A)、5% 甲醛 (F) 组成，可用于植物年老或较坚硬的组织的固定，不用于植物单细胞及丝状藻类等幼嫩材料的固定，可防止材料的过度收缩，固定柔软幼嫩材料时宜用 50% 乙醇代替 70% 乙醇，FAA 固定剂可兼做保存剂。该试剂仅用于科研领域，不适用于临床诊断或其他用途。
操作步骤 (仅供参考)
1、取新鲜组织入 AAF固定液(适用于成熟组织)，置于室温固定 1~12h。
2、常规石蜡切片因固定不佳导致染色效果不满意时，可在染色前再用 AAF 固定液固定 5min，染色效果会有明显提高。
注意事项
1、AAF 固定液对人体有一定的损害，请在通风好的环境下小心操作，避免吸入。
2、组织取材的厚度不同，固定时间也不同，对组织恰当的选材有利于固定液的渗透；常规活检组织比较适合的厚度为 2~4mm，一般不超过 6mm。
3、固定液的容量应足够，一般固定液与组织块的体积比率应大于 10:1；如果容积不够大，可以在固定期间更换 1~3 次固定液。
4、温度对固定的影响很明显，提高温度可以加速固定作用，但温度不宜过高。
5、取出新鲜组织后，应及时固定。
6、试剂开封后请尽快使用，以防影响后续实验效果。
The purpose of fixation is to preserve the original morphological structure of cells and tissues. Fixatives prevent autolysis of tissues and cells caused by endogenous lysosomal enzymes and inhibit the proliferation of bacteria and fungi. Through coagulation and adduct formation, fixatives alter the internal structure of proteins to inactivate enzymes and produce physical changes to cell nuclei and extracellular components. Fixatives are mainly categorized into aldehyde, mercury, alcohol, oxidant and picrate types, among which formalin (aldehyde type) and ethanol (alcohol type) are the most commonly used.
AAF Fixative Solution (For Mature Tissues), also known as 70% FAA/AFA Fixative or universal fixative, is composed of 70% ethanol (A), 5% acetic acid (A) and 5% formaldehyde (F). It is suitable for fixing aged or hard plant tissues, but not for tender materials such as single plant cells and filamentous algae. It can prevent excessive shrinkage of samples. For soft and tender specimens, 50% ethanol formulation is recommended instead of the 70% version. FAA fixative can also serve as a preservative. This reagent is for research use only and not applicable for clinical diagnosis.
Operating Procedures (For Reference Only)
1.Immerse fresh tissues into AAF Fixative and fix at room temperature for 1–12 hours.
2.If paraffin sections show unsatisfactory staining results due to insufficient fixation, re-fix the sections with AAF Fixative for 5 minutes prior to staining to greatly improve staining performance.
Precautions
1.AAF Fixative is harmful to human bodies. Perform all operations in a well-ventilated area and avoid inhalation.
2.Fixation duration varies with tissue thickness. Proper trimming of tissues facilitates penetration of fixative. The optimal thickness of routine biopsy tissues is 2–4 mm and shall not exceed 6 mm.
3.Sufficient volume of fixative shall be prepared; the volume ratio of fixative to tissue block should be over 10:1. If the volume is insufficient, replace the fixative 1–3 times during fixation.
4.Temperature exerts a prominent influence on fixation. Elevated temperature accelerates fixation, yet excessively high temperature must be avoided.
5.Fix fresh tissues immediately after dissection.
6.Use the reagent promptly after opening to prevent compromised experimental outcomes.
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