Erythrosine B (free acid)

Erythrosine B free acid​ (Erythrosin extra bluish free acid; Tetraiodofluorescein) is a visible red dye and insecticide with colorimetric and fluorescent properties. Erythrosine B free acid serves as a membrane-impermeant live-cell dye for Gram-positive and Gram-negative bacteria, primarily staining dead cells with damaged plasma membranes. Erythrosine B free acid exhibits photosensitive larvicidal toxicity against Culex pipiens quinquefasciatus larvae. Erythrosine B free acid is used in live/dead bacterial assays in colorimetric and fluorescent measurements for low-, medium-, and high-throughput experiments, as well as in research related to mosquito-borne diseases and food coloring^[1][2][3][4]. In Vitro:Erythrosine B (0.8%; 5 min) free acid is a membrane-impermeant live-cell dye that selectively stains dead or membrane-damaged Gram-positive and Gram-negative bacteria^[2].
Erythrosine B free acid shows a linear correlation between its absorbance at 530 nm and the proportion of dead cells in E. coli, K. pneumoniae, and P. mirabilis populations, enabling microplate-based quantitative colorimetric viability detection^[2].
Erythrosine B (5 min) free acid is a fluorescent viability dye detectable by flow cytometry that distinguishes live from dead cells across multiple bacterial species and tracks the time-dependent increase in cell death in sodium azide-treated cultures of S. marcescens^[2].
Erythrosine B free acid preferentially binds to the N-terminus of Aβ₄₀ monomer (PDB 1BA4) with a binding free energy of 20.15 kcal mol^-1, disrupts the Asp23-Lys28 salt bridge, and preserves the α-helical structure of residues 13-16 in the PDB 2LFM conformation. At a 2:1 ratio to Aβ₄₀, it further stabilizes the C-terminal α-helix by excluding water molecules, thereby inhibiting the conformational transition to the aggregation-prone β-sheet structure^[4]. In Vivo:Erythrosine B (0.25-12 ppm; added to rearing water for larval ingestion; fed approximately 15 min before light exposure; light exposure up to 24 h) free acid exhibits concentration-dependent and light duration-dependent larvicidal activity against fourth-instar Culex pipiens quinquefasciatus, with a 24 h LC₅₀ of 2.45 ppm, while the addition of 8% SDS enhances toxicity approximately 3-fold, reducing the LC₅₀ to 0.66 ppm^[3].
Erythrosine B (0.25-4 ppm; added to rearing water for larval ingestion; 24-h dark feeding period prior to light exposure; light exposure duration up to 24 h) free acid exhibits approximately 16-fold greater larvicidal efficacy against fourth-instar Culex pipiens quinquefasciatus compared with conditions without dark pre-incubation^[3].