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17 Jun 2002
Optical heterodyne detection could lead to a sensitive high-speed method of assessing new drugs.
Developed by Rick Trebino and colleagues at the Georgia Institute of Technology in the US, the magneto-optical phase enantiomeric detector (MOPED) can distinguish between different optical isomers, known as enantiomers, of the same compound.
Enantiomers are mirror images of each other, and are therefore difficult to tell apart using conventional analysis methods. However, the chemical difference between so-called "D" and "L" isomers often means that only one is active as a drug, while the other is ineffective or even harmful.
Trebino's technique is based on the fact that the molecules in question rotate the polarization of light differently - an effect first noted by Pasteur in the 19th century. Polarimetry is often used to distinguish between these isomers, but the method lacks sensitivity and is too slow for high-throughput screening.
The MOPED method uses laser light passed through a sinusoidally varying magnetic field to interrogate a solution containing a mixture of enantiomers. Using optical heterodyne detection to measure both optical phases of the solution's effect on the laser light, the set-up can pick up very small differences in "enantiomeric excess" (i.e. how much more there is of one type of enantiomer than of the other).
To achieve a similar sensitivity using polarimetry would be impossible, say the researchers.
Author
Michael Hatcher is technology editor of
Opto & Laser Europe magazine.
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