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An assay is a procedure for the determination of the concentration of a particular constituent of a mixture.
DNA
Assays for studying interactions of protein with DNA include:
Protein
Viruses
The number of viruses present in a sample can be determined using a viral plaque assay. This technique requires counting the number of plaques formed by a virus sample, from which the actual virus concentration can be determined.
Cellular secretions
A wide range of cellular secretions (say, a specific antibody or cytokine) can be detected using the ELISA technique. The number of cells which secrete those particular substances can be determined using a related technique, the ELISPOT assay.
Drugs
Illegal drug testing
Environmental contaminants
Coins
A 19th century assay laboratory in Tombstone Courthouse State Historic Park, Arizona. An assayer is often assigned to each mint to determine and assure that all coins produced there have the correct content or purity of each metal in them. This is particularly important with gold and silver coins.
Precious metals
Precious metals, platinum, gold and silver, used in jewellery, silverware and other items, are also assayed to test the purity of the metal, to protect consumers. This is done in the UK by an Assay Office. Once an item has been assayed, it is usually hallmarked to the relevant standard.
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