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26/04/2007
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Tom Shelley reports on a simple and potentially low cost method for detecting small amounts of unwanted chemical substances
A new fluorescence method can accurately detect chemical species down to parts per billion level – yet is fast and simple enough to be used by unskilled technicians.
Operated by pressing only three buttons, it sits within a small grey box and performs functions presently requiring the use of a bench top full of equipment, skilled technical assistance and a great deal more money.
The ‘Toximet T’ system is the brainchild of Raymond Coker, emeritus Professor of Food Safety at the Natural Resources Institute in the University of Greenwich.
It depends on a combination of four advances. The first is to use hard ultraviolet light at 365nm to excite fluorescence in the form of visible blue light. The second is to immobilise extracts of the substance to be analysed in special “Tailored polymer” plugs. These have been developed in conjunction with Cranfield University, and also enhance the fluorescent effect. The third is to scan the plugs mechanically, in such a way as to produce precise and reproducible results. The fourth is to do the whole thing in an instrument that has only three buttons, and which can very quickly and inexpensively produce results that would conventionally require the use of a chromatography system and the expertise to use it.
Prof Croker demonstrated his approach by measuring parts per billion of aflatoxins in peanuts. These are deadly poisons produced by moulds that are “quite common” on a range of foodstuffs including wheat, dried fruit, beer, fruit juice, milk and coffee.
He took the contaminated peanuts and extracted them in a machine similar to a kitchen blender. The filtrate was then sucked into cartridges using a vacuum manifold. Each cartridge was equipped with one of the special polymer plugs, and loaded into the top of the instrument. A crucial feature of the measurement method is that the cartridge passes through the beam in 1 micron increments, making a 360 degree rotation during each increment thanks to a dual motion actuator beneath it. The instrument first does a core scan, and then a second finer scan over the region found to be of interest.
At the start of each days work, the instrument is calibrated using a cartridge containing no toxin, and then a cartridge containing a known amount. The instrument, which was built by Optisense in Horsham, then computes the amount of toxin and displays the amount on an LCD screen. During the demonstration, the internal calibration and measurement graphs were being displayed on a PC, but there is no need for this in normal use. Repeating measurements produced almost identical results, showing that the method is highly reproducible.
Although the method was originally chosen because the toxins of interest are naturally fluorescent, Prof Coker revealed that he is developing potential methods for detecting a wide range of substances and combinations of substances, including chemical species that are not fluorescent, such as “pesticide residues, vitamins, environmental toxins, and counterfeit drugs”.
He added: “The method is appropriate for any application where people want to undertake a rapid, accurate and precise analysis, and where you can immobilise something of interest on a polymer.”
At present, such analyses are usually performed using chromatography systems, which
can cost around £60 per sample, and take one to three weeks for the results to come back. A complete analysis cycle using the Toximet instrument, including the extraction process, takes around 20 minutes.
While the method looks simple, Prof Coker revealed that the path to developing a commercial system has not been easy. He originally obtained a DTI SMART Award that allowed him to build the original “Pre prototype” with assistance from the School of Engineering at Greenwich University. The current machine is the fourth pre-production prototype. Commercial exploitation is now in sight, with around 40 potential customers said to be “very interested”.
The instrument and methods are protected by patents.
Email Toximet
Pointers
* Method uses UV fluorescence to accurately measure amounts of substances down to parts per billion level
* The prototype instrument is small, relatively low cost, simple to use and has only three buttons
* The method is potentially applicable to a very wide range of substances, whether fluorescent or not, provided they can be immobilised on a polymer
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Author
Tom Shelley
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