nigrosin

For bright field microscopy, negative staining is typically performed using a black ink fluid such as nigrosin.

Furthermore, negative staining with nigrosin can reveal some microorganisms that cannot be stained by regular methods.

This can be achieved by smearing the sample onto the slide and then applying nigrosin (a black synthetic dye) or Indian ink (an aqueous suspension of carbon particles).

In biology, nigrosin is used for negative Staining of bacteria., as well as the capsule-containing fungus, Cryptococcus neoformans The shapes and sizes of the organisms are seen as color-free outlines against the dark background.

Nigrosin is a mixture of synthetic black dyes (CI 50415, Solvent black 5) made by heating a mixture of nitrobenzene, aniline and aniline hydrochloride in the presence of a copper or iron catalyst.