Molybdophosphoric acid stain, also known as the molybdate stain or Molybdenum stain, is a commonly used method in histology and microscopy to selectively stain certain structures or substances within a tissue sample. This staining technique is primarily used for visualizing polysaccharides, glycoproteins, and mucopolysaccharides in biological specimens.

The molybdophosphoric acid stain involves the use of a combination of molybdic acid, phosphoric acid, and a reducing agent such as glucose or formaldehyde. The exact composition of the staining solution may vary depending on the specific protocol used.

Here’s a general overview of the staining procedure:

1. Fixation: The tissue sample is first fixed using an appropriate fixative (e.g., formalin) to preserve its structure.

2. Dehydration: The fixed tissue is dehydrated using a series of alcohol washes to remove water from the tissue.

3. Clearing: The dehydrated tissue is then cleared using a clearing agent, such as xylene or toluene, to make it transparent and allow better visualization.

4. Staining: The tissue is immersed in the molybdophosphoric acid staining solution for a specific period of time. The molybdophosphoric acid forms a complex with the targeted substances in the tissue, resulting in a color change.

5. Differentiation: After staining, the tissue is washed with water or a weak acid solution to remove excess stain and to enhance contrast.

6. Dehydration and Mounting: The tissue is dehydrated again using a series of alcohol washes and then mounted on a glass slide using a mounting medium, such as Canada balsam or synthetic resin.

Under the microscope, the stained structures or substances appear as blue or green, depending on the specific protocol and the nature of the targeted molecules.