Use of Congo Red

[BROCSMAN]

I've just bought some congo red, but it arrived as powder, not in solution. Can someone tell me how to prepare it for staining microscope slides?

Thanks

[Paul mabbott]

Originally Posted by BROCSMAN

I've just bought some congo red, but it arrived as powder, not in solution. Can someone tell me how to prepare it for staining microscope slides?

Thanks

It dissolves in water at about 1% (i.e. 1 gram per 100 mls water) and more easily in alcohol (meths, isopropanol) to give a stronger solution.

I'm intrigued to know what you would use it for?

[BROCSMAN]

Thanks for the reply. It's used as a stain to highlight structures in fungi specimens on microscope slides.

[fairplay]

My understanding is you add ammonia, but at what percentage I do not know.

Surely with chemicals, some instructions came or were there on the ordering sheet ?

[mollisia]

Hello,

there are different methods to prepare a Congo Red solution for microscopical staining. The basic problem with Congo Red is, that it should be a saturated solution to achieve best results, but that the Congo Red falls out quite soon again when oversaturated.
The solution in water keeps not too long time before falling out, but stains quite good.
Traditionally it is solved in ammonia, which gives not the best staining results, but the fastest fall-out, because ammonia vaporizes quite fast and the solution gets oversaturated in a short time. The advantage is that the Congo Red solves pretty easily in ammonia.
Clemencon prefers SDS (= Sodium dodecyl sulphate or Lauryl sulphate) for to solve such dyes. SDS has the advantage that the Congo doesn't fall out too fast and the stainig resultats are still better than in water solutions. But it has the disadvantage, that it cannot be used in combination with KOH.
In his newest book "Methods of working with Macrofungi" (it is in english indeed!), he also describes a solution of Congo Red in glycerol-aethanol-boric acid, which may be the best version of all, and is said to be stable several years. I have not tried this yet.

In every case solutions were Congo did fall out can be warmed a little bit, so the Congo will dissolve again.

Congo Red in glycerol-aethanol-boric acid:
1% Congo Red in 1% boric acid with 10% aethanol and 15% glycerol

Congo Red in SDS:
1g Congo Red in 100ml 3-5% SDS in destilled water.

Congo Red in water:
1% Congo Red

best regards,
Andreas

[BROCSMAN]

Well there's a challenge. It must be nearly fifty years since I last tried to make a saturated solution. Wish me luck.

Thanks all.

[paulcarr]

I must add that over my years working in a fungi research lab I found SDS solutions a nightmare for precipitating out of solution so maybe avoid these? I would go for the simplest prep using water and simply give it a quick blast in the microwave to warm and get any precipitate back in solution. I shall try and dig out some methods and stain recipes I have used myself.