The proven ability of gel electrophoresis to simultaneously resolve, in a single experiment, many components from complex biological samples, has determined its preference over a variety of well-established chromatographic methods, Therefore, procedures placed at the interface between gel separation and microanalysis have earned increasing significance with respect to the overall success of the microanalytical strategy. The first of these procedures is the detection technique. The most important requirement for compatibility with further analysis or bioapplications is that the staining method does not compromise the chemical integrity and the biological properties of micropurified biomolecules. Procedures for negative detection of proteins with metal salts that have been proven to comply with this condition have been known for about 15 years. Only recently have these procedures been extended to the field of nucleic acids and lipopolysaccharides. The focus of this review is to chronicle the development and current status of the negative or reverse stain procedure based on the in-gel reaction of imidazole with zinc salts and its applications for the micropurification and analysis of unmodified proteins, nucleic acids and bacterial lipopolysaccharides. We highlight the common aspects in the detection of the three types of biomolecules, and their applications to structural and biological analyses. Emphasis is given on the mechanism underlying imidazole-zinc staining, as it contributes to a deeper understanding of a general detection mechanism with metal salts. Finally, we discuss the latest applications of the techniques in proteomics and their possible impact on the characterization of gel-separated single components from complex lipopolysaccharides.