This article was taken from the June 2012 issue of Wired magazine. Be the first to read Wired's articles in print before they're posted online, and get your hands on loads of additional content by subscribing online.
Each month Wired's chemist Dr John Emsley deconstructs an everyday product. He is the author of 110 research papers and ten books, including his most recent: Nature's Building Blocks, 2nd edition (OUP).
Ingredients -Plastic housing
-Absorbent tip
-Immunoassay strip
-Gold nanoparticles
-Monoclonal antibodies
How the pregancy test works
The test detects human chorionic gonadotropin (hCG), a hormone that's excreted in urine after a fertilised egg implants in a woman's uterus. It is a peptide polymer of 244 amino acids, part of which is unique to hCG. It can be detected with 99 per cent accuracy.
Absorbent tip Urine must come into contact with the tip for ten seconds for an accurate reading. It absorbs the liquid, which travels into the device along the immunoassay strip.
Gold nanoparticles The test's active agent. Measuring 10^-9m, they appear red because of the way they interact with light, and give the indicator strip its colour.
<span class="s1">Plastic housing
The plastic protects the test strip and consists of a coloured polymer with an in-built polycarbonate window where the test results are displayed.
Immunoassay strip This consists of compressed polymer fibres. The urine travels along it by capillary action and comes into contact with antibodies that can detect hCG.
Monoclonal antibodies
These are grown in vitro and are designed to identify hCG. They attach themselves to the gold if hCG is present, and move up the strip until they reach the indicator.
This article was originally published by WIRED UK
