<unk>  is a biochemical technique of adding a class-specific (DNA, proteins, lipids, carbohydrates) dye to a substrate to qualify or quantify the presence of a specific compound. It is similar to fluorescent tagging.
Stains and dyes are frequently used in biology and medicine to highlight structures in biological tissues for viewing, often with the aid of different microscopes. Stains may be used to define and examine bulk tissues (highlighting, for example, muscle fibers or connective tissue), cell populations (classifying different blood cells, for instance), or organelles within individual cells.
Biological<unk>  is also used to mark cells in flow cytometry, and to flag proteins or nucleic acids in gel electrophoresis.
Staining
Grading 
Formication
Reading
Dosing
Solution
Splitting 
Writing