[Histonet] Alkaline NaCl saturated Congo Red Procedure (Puchtler et al. 1962)


Dear Histonet Members,

could someone please explain to me the purpose/effect of alkalinization by 
adding 1 ml of 250 mM NaOH to 100 ml of the staining solution used in 
Puchtler's alkaline, NaCl-saturated Congo Red staining method?
Accidentally, I once forgot to add the NaOH, but the staining results did 
not differ from those that we usually obtain when we stick to the 
alkalinizing protocol. Can one omit the alkalinization without doing any 
harm to the method's nice sensitivity and specificity towards amyloid 
and/or reproducibility of staining results? What is the alkalinization 
intended to be good for?
This question is aimed at some practical consequences: Omitting the 
alkalinization step would (i) save time, (ii) spare using corrosive agent 
(NaOH), (iii) leave the staining solution more stable (than for less than 
one day with NaOH added) and thus (iv) save staining reagents 
(particularly expensive ethanol) and congo red dye.

Thank you for your expert opinion.

Best regards,


Dr. Joachim Velden
Evotec Neurosciences GmbH
Schnackenburgallee 114
D-22525 Hamburg

Phone +49-40-56081-394        Fax +49-40-56081-222
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