Phloxine B (Powder)

Technical Specifications

Product Description & Scientific Applications

Phloxine B is the tetrabromo, tetrachloro derivative of fluorescein, a red xanthene dye also designated D&C Red No. 28 and used as a colorant in drugs, cosmetics, and, in some countries, foods. Visible light turns it into a photosensitiser: it generates singlet oxygen with a quantum yield of 0.59 in D₂O, and its bromine and chlorine substituents make it a far more efficient singlet-oxygen generator than the less-halogenated dichlorofluorescein, whose yield is 0.06. Photoexcitation proceeds mainly by a Type-II, singlet-oxygen route, with a minor radical pathway yielding superoxide, a semiquinone radical, and hydrogen peroxide; these species oxidise membrane lipids and damage DNA.

Common Scientific Applications

Phototoxic insecticide. Phloxine B is a light-activated bait toxicant for tephritid fruit flies, and its action requires the insect to ingest the dye. In medfly larvae, light lowers the lethal concentration more than twenty-fold (dark LC₅₀ 11.03 mM versus 0.45 mM after light exposure), the effect is dose-dependent, and the dye damages larval muscle. As an environmentally safer alternative to malathion, field bait sprays against Mexican, West Indian, and Mediterranean fruit flies match malathion-bait efficacy, with the protein carrier strongly affecting performance. Against melon and oriental fruit flies it requires higher concentrations than spinosad; adjuvants such as Tween 60 lower the effective dose and shorten the time to kill.

Antimicrobial photoinactivation. Under illumination, phloxine B permeabilises bacterial membranes. It drives potassium leakage from Staphylococcus aureus within minutes and collapses the membrane potential, acting through singlet oxygen and binding to the cells; among common xanthene dyes its membrane activity is second only to rose bengal. Loaded into poly(2-hydroxyethyl methacrylate) films, it works as a solid-supported photosensitiser, its singlet-oxygen output peaking near 2 wt% as fluorescence self-quenching sets in above 0.1 wt%.

Cell-viability reporter in yeast genetics. Phloxine B stains non-viable yeast cells without affecting living ones, so the redness of a colony marks its dead-cell fraction; this gives a viability score used across large Schizosaccharomyces pombe gene-deletion fitness screens, and it also separates diploid colonies from haploid ones. In fission yeast the dye acts as a light-dependent pro-oxidant: under illumination it raises protein carbonyl content and transiently depletes reduced glutathione, and a superoxide-dismutase-deficient (sod1) mutant is hypersensitive.

Differential bacterial stain. Phloxine B separates Gram-positive from Gram-negative bacteria in under two minutes, read by eye or under bright-field, fluorescence, or confocal microscopy, giving a rapid alternative to the Gram stain; its staining tracks its bactericidal action. In histology it is the red component of Lendrum's phloxine–tartrazine method for acidophilic inclusion bodies.

Ion-channel probe. In electrophysiology, phloxine B modulates the CFTR chloride channel at several sites: low-micromolar concentrations raise the channel's open probability, while higher concentrations block the pore in a voltage-dependent manner.

Shipping Destinations

• EU & UK: Priority delivery, 2–5 business days.
• United States (DDP): 3–7 business days, duties and taxes prepaid.
• EFTA Countries (DDP): 3–7 business days, duties and taxes prepaid.
• Worldwide: 7–14 business days, selected locations.