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17 Jun 2002
Biological and chemical sensors that can detect extremely small concentrations are possible with fluorescent polymers.
Chemists at Los Alamos National Laboratory and the University of California have discovered that just one 'quencher' molecule, which usually combines with one specific part of another molecule to stop its fluorescence, can 'switch off' the light from a whole polymer chain which has thousands of fluorescent sites. This means that chemical sensors based on fluorescent polymers can be more than a million times more sensitive than previously expected.
The researchers studied the conjugated polymer poly (2-methoxy-5-propyloxy sulfonate phenylene vinylene). When green light is shone onto a solution of the polymer it glows orange. If a tiny concentration of a particular molecule - called a 'quencher' - is added to the solution the light is turned off. Because their concentration is low, the quencher molecules can be easily removed by adding another compound, making the system reversible.
Quencher molecules provide a route for the polymers to lose energy without emitting it as light. In this case, one such molecule can provide an alternative energy route for the whole polymer because the electrons can move very freely along the chain.
By attaching different chemical groups to the quencher molecules they can be modified in this way to selectively detect different species. The researchers used the system to detect a protein called avidin. The quencher molecule was connected to the vitamin biotin, which strongly binds to avidin, so that if the protein was present in the solution they would bind together. This makes the quencher too big to get close to the polymer and stop the fluorescence.
This research was reported in the 26 October 1999 issue of Proceedings of the National Academy of Sciences.
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