A diazo dye used as a pH indicator or to label amyloid plaques
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Congo Red

Item No. 45550

Product Insert (PDF)Safety Data Sheet (SDS) (PDF)
Technical Information
Formal Name
3,3′-[[1,1′-biphenyl]-4,4′-diylbis(2,1-diazenediyl)]bis[4-amino-1-naphthalenesulfonic acid, disodium salt
CAS Number
573-58-0
Synonyms
  • Direct Red 28
Molecular Formula
C32H22N6O6S2 • 2Na
Formula Weight
696.7
Emission
620 nm
Excitation
596 nm
Formulation (Request formulation change)
A solid
Solubility(Learn about Variance in Solubility)
DMSO: Sparingly soluble: 1-10 mg/mlPBS pH 7.2: Slightly soluble: 0.1-1 mg/ml
λmax
230, 338, 500 nm
SMILES
O=S([O-])(C1=CC(N=NC2=CC=C(C3=CC=C(C=C3)N=NC4=C(N)C5=C(C=CC=C5)C(S(=O)([O-])=O)=C4)C=C2)=C(C6=C1C=CC=C6)N)=O.[Na+].[Na+]
InChi Code
InChI=1S/C32H24N6O6S2.2Na/c33-31-25-7-3-1-5-23(25)29(45(39,40)41)17-27(31)37-35-21-13-9-19(10-14-21)20-11-15-22(16-12-20)36-38-28-18-30(46(42,43)44)24-6-2-4-8-26(24)32(28)34;;/h1-18H,33-34H2,(H,39,40,41)(H,42,43,44);;/q;2*+1/p-2
InChi Key
IQFVPQOLBLOTPF-UHFFFAOYSA-L
Shipping & Storage Information
Storage
-20°C
Shipping
Wet ice in continental US; may vary elsewhere
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    25 g

    $25

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    50 g

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    100 g

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    Product Description

    Congo red is a diazo dye.1 It has been used as a pH indicator and produces a red color in weakly acidic or basic solutions (pH ≥5), changing to violet or blue under strongly acidic conditions (pH ≤3). Congo red has also been used in the detection of amyloid plaques in animal models of Alzheimer’s disease via both brightfield and fluorescence microscopy. It displays excitation/emission maxima of 596/620 nm, respectively.2 Congo red reduces toxicity induced by amyloid-β (1-40) (Aβ40) in primary rat hippocampal neurons (EC50 = 0.5 µM) and increases survival, reduces polyglutamine aggregates, and improves gait in a mouse model of Huntington’s disease.3,4 Formulations containing Congo red have been used as histological stains for amyloid in various amyloidosis conditions.

    WARNING This product is not for human or veterinary use.

    References & Product Citations
    Product Description References

    1. Sarkar, S., Raymick, J., Cuevas, E., et al. Modification of methods to use Congo-red stain to simultaneously visualize amyloid plaques and tangles in human and rodent brain tissue sections. Metab. Brain Dis. 35(8), 1371-1383 (2020).

    2. Clement, C.G., and Truong, L.D. An evaluation of Congo red fluorescence for the diagnosis of amyloidosis. Hum. Pathol. 45(8), 1766-1772 (2014).

    3. Burgevin, M.C., Passat, M., Daniel, N., et al. Congo red protects against toxicity of β-amyloid peptides on rat hippocampal neurones. Neuroreport 5(18), 2429-2432 (1994).

    4. Frid, P., Anisimov, S.V., and Popovic, N. Congo red and protein aggregation in neurodegenerative diseases. Brain Res. Rev. 53(1), 135-160 (2007).