Question

What other stains besides Congo red work as a negative stain? What chemical property would they all share?

What would be the result if after a negative stain was prepared, on of the simple stain dyes was added to the slide?

Answer 1

Stains like Indian ink and nigrosin are commonly employed as negative stains .The staining procedure is used to visualize thin specimens where in the process the background is stained by these dyes and the specimen is not stained .So under a microscope the unstained part represents the specimen.

The chemistry is these stains should be such that they should contain an acidic part when this part can easily lose electrons or protons.This will inturn turn the chromophore negative which results absorption of light in visible spectrum thereby enhancing its visualization.

When a negative dye is added on a simple dye in a slide the specimen is first stained by the simple dye and the background by negative staining.