Neon Formazans along with Tetrazolium Salts - Toward Neon Cytotoxicity Assays. Formazan-based colorimetric cytotoxicity assays, for example the MTT assay, are typically used to assess mobile viability with only metabolically lively tissues decreasing tetrazolium salt into the formazans, that is next quantified by absorbance. Fluorescence gives several advantages in comparison