Negative staining, also known as negative staining, is discovered by Hall relative to the ordinary staining (i.e. positive staining) staining technique, the principle lies in the use of heavy metal salts around the low electron density of the sample, enhance the electron density around the sample, resulting in the “mass-thickness” difference between the fine structure, enhance the scattering absorption contrast, so that the sample shows a bright structure on the dark background. Enhance the scattering absorption contrast, so that the sample in the dark background presents a bright structure, negative staining solution has phosphotungstic acid, ammonium molybdate, India ink, etc., of which the most commonly used is 1 ~ 3% phosphotungstic acid.

Ammonium molybdate negative staining solution (3%, pH7.0) is suitable for displaying macromolecules, bacteria, viruses, protozoa, phages, organelles, nucleic acid macromolecules, protein crystals and other macromolecular materials, etc. The stained image of the sample shows a transparent bright light, while the background image is black.