Something stinks

Using special polymers, scientists are on trying to make an 'artificial nose'

Published: Monday 15 March 1999

A soldier wearing a WWI gas ma gasmasks were first introduced during the First World War as precautionary measures for soldiers. And though weapons have become much smarter, advanced and lethal since then, gasmasks still remain where they were almost a century ago. Most gasmasks available today use one or several filters to purify the air the wearer breathes in. These might be acceptable in regular industrial circumstances where contaminated air is not a problem. But in situations that demand more stringent air purification, a biochemical weapons site for instance, these masks offer very little protection against minute germs and viruses.

Now, us -based scientists have developed 'intelligent' chemical gatekeepers that only admit certain types of molecules. These gatekeepers could soon find their way into gasmasks and better chemical weapons or pollution sensors. These new "access ports" will guide the target molecules to an inner compartment to be trapped and tagged.

The development was the achievement of Ken Suslick and his team at the University of Illinois, usa . Suslick and his team toyed with a curious substance called dendrimer. These are self-assembling polymers that branch out in different directions from a single molecule. The team attached these dendrimers to a porphyrin, an organic molecule with a metal binding site that can trap other substances.

Suslick's team has used zinc as the active metal site in their porphyrin. It functions quite like a haemoglobin molecule in the bloodstream containing iron for transporting oxygen in mammals. The dendrimers formed two types of access ports leading to the porphyrin binding site. One, shaped like a chimney, only lets in slender, thinner molecules. The other, cave-like, admits short, fat molecules. "We can choose between short fat molecules or long skinny ones," says Suslick. The porphyrins changed colour when they bound to their chosen targets, in the same way that haemoglobin turns red when it binds to oxygen and blue when oxygen is released, reported a recent issue of Journal of the American Chemical Society . How soon can the new technique be used commercially for safer, more accurate sensors? Right now, the team is working on 'artificial noses'. "It's the sort of thing you could use in the food industry, in the chemicals industry or as detectors for chemical warfare agents," says Suslick. He adds that when arranged in an array, the ports could be used to let in specific molecules -- a big help to any reaction that might require a catalyst.

The technique has impressed Jean Frechet, a dendrimer specialist at the University of California in Berkeley, usa . "They've shown that by using dendrimers in bulk, they can control what you let into the binding site," he says ( New Scientist , Vol 161, No 2169).

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