Neutral red is a weakly alkaline pH indicator, color change range between pH 6.4 to 8.0 (from red to yellow), molecular formula C15H16N4?HCl, molecular weight of 288.78, in a neutral or slightly alkaline environment in the living cells of the plant can be a large number of absorption of neutral red and excretion of the vesicle, due to the vesicle is in general an acidic reaction, so that into the vesicle of the neutral red dissociate a large number of Because the vesicle is generally acidic, the neutral red in the vesicle dissociates a large number of cations and takes on a cherry red color, in which case the protoplasm and cell wall are generally not colored. Dead cells due to the degeneration of protoplasm coagulation, the cytosol can not be maintained in the vesicle, with neutral red staining does not produce vesicle coloring phenomenon, on the contrary, the cations of neutral red, but with a certain degree of negatively charged protoplasm and nucleus binding, and make the protoplasm and the nucleus of the cell staining.

Neutral red staining solution (for living cells) is neutral, and is a staining solution commonly used for staining tissues or cells to turn the nucleus red. Nucleic acids and lysosomes in the nucleus are acidic, and therefore the nucleus will be stained red.