The Nissl staining is a classic dye combination mostly binding to nucleic acid and staining it in dark blue to purple. The Nissl staining is most well known for its use in nervous tissue histology.
The Nissl staining employs a mixture of basic dyes (aniline, thionine, or cresyl violet) which stains negatively charged RNA.
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.