Microwave Procedures for Electron Microscopy and Resin-Embedded Sections

Abstract

Microwaves now have well-established applications in routine light microscopy. They are employed in tissue fixation and to accelerate a wide spectrum of staining procedures. Besides producing superior preservation of cellular antigens through microwave fixation, this form of irradiation has been employed for antigen retrieval, a procedure that has been a major factor in the optimization of immunolabelling in paraffin sections and cytological preparations. A commercial tissue processor has recently been developed which employs microwaves in a markedly accelerated, one-step processing of tissue blocks, completing the procedure within a fraction of conventional times. Microwaves have also been successfully applied in a variety of molecular techniques such as in situ hybridization and polymerase chain reaction. The adoption of microwaves in electron microscopic procedures has been slower, largely because the requirement for speed in processing is not as great, except in diagnostic samples. However, as this review will show, there are equally as many innovative applications of microwaves in electron microscopy. Microwaves have been employed for rapid processing of fine needle aspiration biopsy samples, in keeping with the requirement for speed in this method of diagnosis. Ultrafast fixation of tissue samples has resulted in the better demonstration of cellular enzymes and proteins. It has been clearly shown that microwave-stimulated on grid staining in uranyl acetate and lead citrate produces more consistent results and without background precipitation. Microwaves can be used to hasten resin polymerization and exposure to microwaves results in antigen retrieval in both resin-embedded thick sections and for immuno-electron microscopy. Immunolabelling shows enhanced sensitivity and the technique is anticipated to contribute greatly to the optimization of immuno-electron microscopy. The potential for greatly accelerated preparation of samples for electron microscopy exists but is yet to be fully realized.