Chemical identity
- IUPAC name: 4-(dimethylamino)‑2‑(dimethylamino)‑5‑dimethylammonio‑1‑naphthalenesulfonate (sodium salt)
- Common synonyms: Janus Green, Janus Green B, Janus Green B sodium salt
- Molecular formula: C₂₇H₃₀N₃O₂S·Na
- Molar mass: ≈ 361 g·mol⁻¹ (anhydrous sodium salt)
- Physical appearance: Deep blue‑green solid, hygroscopic, readily soluble in water and ethanol.
- Spectral properties: Absorption maximum (oxidized form) near 610 nm; reduced (leuco) form is essentially colorless.
Historical background
Janus Green B was introduced in the early 20th century as a vital (supravital) dye for microscopic staining. The name “Janus” refers to the Roman two‑faced god, reflecting the dye’s reversible redox‑dependent colour change.
Applications
| Field | Primary use | Description |
|---|---|---|
| Histology / Cytology | Mitochondrial staining (supravital) | The oxidized dye is taken up by living cells and accumulates in mitochondria, appearing green‑blue under light microscopy. Reduction within active mitochondria converts the dye to a colourless leuco form, allowing assessment of mitochondrial activity. |
| Cell viability assays | Redox indicator | In vitro assays (e.g., for bacterial or mammalian cell cultures) employ Janus Green B to monitor metabolic activity; viable cells reduce the dye, leading to a measurable decrease in absorbance. |
| Spectrophotometric enzyme assays | Electron‑transfer indicator | Used to follow enzymatic reactions that involve NADH/NAD⁺ or other redox couples, where the dye’s colour change provides a convenient read‑out at 610 nm. |
| Aquaculture / Water quality | Detection of dissolved oxygen | Because the reduced form is colourless, the dye can serve as a visual indicator of oxygen levels in water samples; high oxygen maintains the coloured oxidized state. |
| Microscopy (light and fluorescence) | Counterstain | Occasionally combined with other dyes (e.g., crystal violet) to differentiate cell structures in mixed preparations. |
Mechanism of action
Janus Green B is a redox‑active phenazine‑type dye. In its oxidized state it exhibits a deep green‑blue colour; reduction (by cellular reductases, NADH, or chemical reductants) breaks the conjugated system, rendering the molecule colourless. The reversible interconversion makes it useful as a non‑destructive indicator of metabolic activity.
Safety and handling
- Hazards: Classified as irritant to skin and eyes; may cause respiratory irritation.
- Recommended precautions: Use gloves, lab coat, and eye protection; handle in a well‑ventilated area or fume hood.
- Disposal: Collect waste solutions containing Janus Green B as hazardous chemical waste according to institutional and regulatory guidelines.
References (selected)
- Sigma‑Aldrich product datasheet for Janus Green B (S‑200).
- J. Histochem. Cytochem. 1975, 23(6), 401‑409 – “Supravital staining of mitochondria with Janus Green B”.
- Methods in Enzymology, Vol. 290 (1998) – “Redox indicators in spectrophotometric assays”.
All statements are based on established scientific literature and commercial product documentation. No speculative information is presented.
