ABSTRACT
Dye and nondye reagents can directly attach to biological components by strong covalent bonds. Such reactive dyes and fluorescent reagents represent an interesting category of microscopic stains for fixed or living cells and tissues. Classic histochemical examples of reactive staining include demonstration of aldehyde groups with Schiffs reagent, and the detection of thiols by mercurial dyes. Fluorescent labels are also attached to biomolecules, to aid analysis of their interaction with biological substrates. In particular fluorescein isothiocyanate and tetramethylrhodamine isothiocyanate are common fluorescent labels for antibodies and other proteins. Fluorescent labels incorporated into calcifying tissues can provide time-markers for the study of bone and tooth development. Fluorescent labeling of biomolecules has many important applications, and these, together with the chemistry of fluorescent labels, have been reviewed by Haugland RP. Fluorescent labels can be replaced with diachromic colored deposits by photochemical conversion. This involves irradiation in the fluorescence microscope in the presence of diaminobenzidine.
