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Used
to tag biological molecules,
and "measuring between five and ten nanometres
across, are made up of three components. Their cores contain paired clusters of atoms
such as cadmium and selenium that combine to create a semiconductor. This releases light of a
specific colour when stimulated by ultraviolet of a wide range of frequencies.
These clusters
are surrounded by a shell made of an inorganic substance, to protect them.
The whole thing is then coated with an organic
surface, to allow the attachment of proteins
or DNA molecules.
By varying the number of atoms in
the core, qdns can be made to emit light of different colours." [From
The Economist print edition]
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