Different amino acids with different chemical properties of the side chain groups, some with basic side chain, some with acidic side chain, the resulting composition of the protein has a different number of basic groups and acidic groups, these groups will make the protein in different pH solutions with different net charge, the whole protein molecule with more positive charge, that is, basic protein (isoelectric point bias acidic); the whole protein with more negative charge, that is, acidic protein (isoelectric point bias acidic). The whole protein molecule is more positively charged, i.e., basic protein (isoelectric point is acidic); the whole protein is more negatively charged, i.e., acidic protein (isoelectric point is acidic). Using the dual nature of proteins (acidity and alkalinity) and the ability to form salts with acidic and basic dye ions, all proteins can be stained with solid green at pH=2.2 (i.e., all proteins under the isoelectric point); basic proteins are stained with solid green in the range of pH=8.1~8..2.

Acidic protein staining solution utilizes acidic proteins in combination with the positively charged acidic dye solid green for staining, and the most abundant acidic proteins in the cell are mainly found in the cytoplasm and nucleolus, so that most of the cytoplasm and nucleolus are stained green after staining. Since the acidic condition of pH 2.2 is below the isoelectric point of all proteins, all proteins can be stained with solid green, therefore, the acidic protein staining solution is also called total protein solid green staining solution.