The Nissl staining is a classic nucleic acid staining method traditionally used on nervous tissue sections. The active dye in the staining solution can vary, but toluidine blue or cresyl violet are common components.
A basic dye (aniline, thionine, or cresyl violet) binds to negatively charged nucleic acids like RNA and DNA.
Target of the dye
Nissl staining typically marks the ER due to ribosomal RNA as well as the nucleus and other accumulations of nucleic acid.