Methods of microwave fixation for microscopy. A review of research and clinical applications: 1970-1992

Abstract

Microwave fixation methods are important because excellent preservation of both cell structure and antigenicity can be attained several orders of magnitude faster than by routine chemical fixation methods. Fast and ultrafast microwave fixation have yielded significant logistic advantages over another fast fixation approach-rapid freezing at liquid helium temperatures. For example, specimens used for microwave fixation can be as large as 1 cm3 and cells can remain in suspension. We review in detail both qualitative and quantitative morphologic results obtained by using microwave fixation in sample preparation. We provide tables of biological molecules that are preserved in a variety of human and animal tissues by various microwave fixation methods for histochemistry, immunohistochemistry, cytochemistry, immunocytochemistry, and affinity labelling studies. Limitations of large cavity (e.g., household) microwave ovens often result in irreproducible fixation results. We present calibration and standardization protocols for microwave fixation in large cavity microwave ovens that emphasize a) localization of oven hot spots (i.e., high power) using a neon bulb array, b) magnetron warm-up, c) the use of a water load, d) the use of an agar-saline-Giemsa model to predict the uniformity of irradiation in small samples, e) the use of specimen containers with one dimension less than 1.5 cm, and f) fast specimen handling to prevent conductive heating artifacts after irradiation. Although microwave ovens are commonplace their unique applications in the laboratory environment require special safety considerations, which are reviewed. Advances in microwave technology are providing new means to study the structure-function relationships of cellular and biochemical activities.