Simply stated, dyes are substances capable of imparting color by chemically or physically binding with materials (including biological tissues). The ability of dyes to impart color to materials is due to the presence of color bearing chemical groups called chromogens.
For tissue staining to occur, chromogens in a dye solution must bind to the desired elements through one of two processes:
- Absorption - A physical process by which the dye dissolves directly into desired elements in the sample.
- Adsorption - A chemical process by which the dye binds to elements in the sample that have an affinity (chemical attraction) for the dye.