Cell uptake of neutral red depends on the ability of living cell cells to maintain pH gradients. At physiological pH conditions, the net charge of neutral red dyes is almost zero, allowing them to penetrate the cell membrane into the cell through non-ionic passive diffusion. The proton gradient in lysosomes causes the pH in the lysosomes to be lower than the cytoplasm, thus allowing neutral red to be charged and accumulate in the lysosomes. When cell proliferation is accelerated, the number of cells increases, and the amount of neutral red that can be ingested increases. When cells are damaged, the uptake of neutral red decreases. After a certain period of ingestion, the cells are cleaned and cleaved with lysate to release neutral red for detection. In this way, the proliferation or toxicity of cells can be determined by measuring their intake of neutral red.

Cell Proliferation and Cytotoxicity assay kit (Neutral Red assay) is a test kit that detects cell proliferation or cytotoxicity based on a cell's ability to ingest neutral red. This product is stable, not easy to precipitate and has good repeatability.