I've been meaning to write this up ever since I retired - then I discovered that my full notes were wiped by the school IT before my replacements could print it out - then I found some notes and reagents in my shed a couple of years ago.
My idea was to make something that could give an idea of the ABO differntiation but without the cost and without any nasty chemicals. I believe that I succeeded.
This is NOT an agglutination reaction, so it does not mimic the Eldon cards or other similar biological tests. It is much more akin to ‘blue line’ pregnancy tests.
This was made from about 80% glycerol and 20% water. This gave a realistic ‘gloopiness’
The red colour was a red food colour known as a ‘lake’. These are well known precipitates that are made in the presence of strong dye solutions. As the precipitate drops out of the solution some of the dye is trapped in the structure and is no longer soluble. This is why smarties no longer work for chromatography experiments and eating them no longer stains the tongue (as much). If you read the ingredients of smarties, skittles etc. you will see a long list of lakes.
The red colour was one of several that I tried from an ebay supplier of food/cosmetic colours. The ones that didn’t work failed because they had ferric oxide as an ingredient, and one of the tests was for iron salts!
Now for the interesting bit – the antigens.
A is potassium ferrocyanide (Potassium hexacyanidoferrate(II) ) - sharp intake of breath. Despite the name. this stuff is NOT toxic, it is used as an anti-caking agent added to table salt. The beauty of it is that it gives a bright blue reaction when it meets a ferric salt (the original blueprint), so the anti-A is weak ferric citrate (or even Irn-Bru).
B is thymolphthalein, almost identical to phenolphthalein in every respect except that it turns blue on exposure to anti-B, which is sodium carbonate solution.
O blood obviously has neither of the above while AB has both.
The method of determining involves a microscope slide sized piece of blotting paper (I got mine from Rymans) with a pencil mark in the centre, A written near one end and B near the other. A drop of ‘blood’ is placed in the centre and, because the ‘blood cells’ (red lakes) are not soluble they stay put while the ‘serum’ (glycerol + antigens) diffuse both ways outwards. After a short while, a drop of each of anti-A and anti-B are dropped onto the pencil marks and allowed to diffuse towards the ;serum’. When they meet they will give a blue line for positive or nothing for negative.
Other uses of the same blotting paper technology that I tested were:
Essentially identical blood without the red colour, now called serum, urine, wine or whatever you choose, which is tested for drugs, performance enhancing dope or poison.
I also tried it with Benedicts or Fehlings, (Can’t remember which) using a heatproof cooking sheet and an electric iron to develop it. All I can remember were the labels on the ‘urine’ specimen bottles – Mustapha Whee, Anita P, N Uresis, I N Continent, Dai Abieties, M Bustin etc. etc.