Toluidine blue (C.I. 52040) is a cationic dye used in general staining procedures. It stains the extracellular matrix, mostly cartilage, because it labels glycosominoglycans and proteoglycans. It is also useful to observe osteblasts, taste buds and chromosomes. Furthermore, it shows metachromasia, which is useful in plant tissues to distinguish primary cell walls from secondary cells walls. Molecularly, toluidine blue is a thiazine dye.
Procedure
0,5 g toulidine blue (C.I. 52040)
1 ml glacial acetic acid
99 ml distilled water or acetate buffer pH 4
Notes
The optimal pH is about 3 - 5,5, depending on the fixative and type of tissue. The staining time is about 3 min The dehydration has to be fast. Otherwise, the staining is faded out. That is why dehydration starts with 95 º ethanol.
The fading of the staining during dehydration can be prevented by incubation in 5 % ammonium molibdate in distilled water for 5 min. Thus, dehydration can be performed without loosing color.
Most structures, such as nuclei and carbohydrates, are stained in blue, but other colors may appear due to metachromasia.
Products
Toluidine blue (C.I. 52040)
Glacial acetic aci
Acetate buffer
Distilled water
Labware
Test tube
Balance
Magnetic stirrer
pH meter
Flasks
Bottles