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Neutral Red Cell Culture Tested Product Number N4638 Storage Temperature 2-8 °C Product Description Molecular Formula: C15H17ClN4 Molecular Weight: 288.8 CAS Number: 553-24-2 C.I. Number: 50040 1 λmax : 539-544 nm (50% ethanol, 0.5% acetic acid) 1 Synonyms: toluylene red, basic red 5 Neutral Red is a weak cationic azine dye that is used extensively as a nuclear stain in a variety of biological stain applications. It is a pH indicator as well, changing color from red to yellow over the pH range 1,2 6.8-8.0. It is also incorporated into bacteriological growth media. This product is often used for supravital staining of fresh peripheral blood. It can also be used for staining 3 Nissl granules of neuroglial cells. However, this stain in not as permanent as another dye, Cresyl Violet acetate, for this application. Buffered 0.5% Neutral Red solutions are used as a counterstain for Naphthol 4 AS acetate esterase, peroxidase and iron stains. Solutions can also be used to stain plankton for 5 viability. Using 1 part Neutral Red to 10,000 parts sea water, dead cells were stained red and live cells remained unchanged. In addition, aqueous solutions of Neutral Red (0.1% in saline, pH 6.5) can be used as 3,6 a fluorescent stain for lipids . Lipids will fluoresce blue-geen or yellow, depending on their composition. It has been used also as a Twort's stain for parasites 8 in combination with Light Green SF, as a general histological stain for embryonic tissue in combination 9 with Janus green, and for demostrating hydrolysis of 10 fats. It can also be used in conjunction with Luxol Fast Blue for staining tissues embedded in glycol methacrylate: myelin sheaths stain blue, connective tissue stain blue to light purple, and nuclei and 3 cytoplasmic basophilic structures are red. Neutral Red is most commonly used for cytotoxicity 7 assays to determine cell viability. The dye readily penetrates cell membranes of viable cells by diffusion and accumulates in the lysosomes. After the cells are allowed to incorporate the dye, they are briefly washed or fixed. The incorporated dye is then released from the cells and quantitated spectrophotometrically. The change in the level of dye incorporation reflects an increase or decrease in the number of viable cells or their physiological state. This indicates the degree of cytotoxicity caused by the test material, making it possible to distinguish between viable, damaged, or dead cells. This assay forms the basis for the In Vitro Toxicology Kit, Product Code TOX-4. Precautions and Disclaimer For Laboratory Use Only. Not for drug, household or other uses. References 1. Sigma-Aldrich Handbook of Stains, Dyes, and Indicators, Green, F. J., Aldrich Chemical Co. (Milwaukee, WI: 1990), p. 504. 2. Conn's Biological Stains, 9th ed., Lillie, R. D., Williams and Wilkins (Baltimore, MD: 1977), p. 378. 3. Staining Procedures, 4th ed., Clark, G., ed., Williams and Wilkins (Baltimore, MD: 1981), pp. 142-143. 4. Atlas of Cytochemistry & Immunochemistry of Hematologic Neoplasms, Sun, T., et al., American Society of Clinical Pathologists Press (Chicago, IL: 1985). 5. Crippen, R. W., and Perrier, J. L., The use of Neutral red and Evan's blue for live-dead determinations of marine plankton. Stain Technol., 49(2), 97-104 (1974). 6. Kirk, P. W., Jr., Neutral red as a lipid fluorochrome. Stain Techol., 45(1), 1-4 (1970). 7. 8. Borenfreund, E., and Puerner, J. A., Toxicity determined in vitro by morphological alterations and neutral red absorption. Toxicol. Lett. 24(2-3), 119-124 (1985). Twort, F. W., An improved neutral red, light green double stain, for staining animal parasites, microorganisms and tissues. J. State Med. (London), 32, 351-355 (1924). 9. Faris, H. A., Neutral red and janus green as histological stains. Anat. Rec., 27, 241-244 (1924). 10. Knaysi, G. Further studies on the use of basic dyes for measuring hydrolysis of fats. J. Dairy Sci., 25, 585-588 (1942). CMH/RXR 5/06 Sigma brand products are sold through Sigma-Aldrich, Inc. Sigma-Aldrich, Inc. warrants that its products conform to the information contained in this and other Sigma-Aldrich publications. Purchaser must determine the suitability of the product(s) for their particular use. Additional terms and conditions may apply. Please see reverse side of the invoice or packing slip.