Scientists are working on a detection test which they say could be a quick way of spotting dangerous contamination of food or water.

Since 11 September, many experts have warned of the threat of terrorist attack with highly destructive pathogens such as smallpox or anthrax.

However, other warnings focus on the potential disruption which might be caused by attacks with more common bacteria such as E. coli and salmonella.

If meat or water were to be deliberately contaminated with these bugs, large numbers of people could be struck down with debilitating illness.

The problem with many current tests is that they can take days to carry out, as sufficient numbers of bacteria have to be cultured to provide a positive result.

A team of researchers from Clemson University in South Carolina, US, is working on a nano-scale test which should not only provide an instant verdict, but also be easy even for the public to use.

Locks on

It uses a small, luminescent protein molecule which has been modified so that it attaches itself to the surface of the target bacterium.

This would work in a similar fashion to an immune system antibody, designed to lock on to a particular feature on the "coat" of the microbe.

In this case the higher the number of connections between bacteria and molecules, the more intense the glow produced.

It could be something you could use at the supermarket checkout

Professor Anne Glover, University of Aberdeen

Dr Paul Dawson, leading the research, said: "The particle's extremely small size increases the odds that the antibody and antigen will link, enabling the sensor to give off a glow."

The results of the test would not be conclusive, he said, but would give an early warning of possible contamination.

"What's needed is a simple, low cost way to rapidly detect pathogens at the site of contamination, not having to wait for lab results."

Supermarket sweep

Professor Anne Glover, from the University of Aberdeen, UK, told BBC News Online that bioluminescence might have some advantages in a simple test for bacteria.

She said: "It is certainly easy to measure; the technology exists to do this and it can be miniaturised.

"It could be something you could use at the supermarket checkout."

However, she warned that the natural ability of microbes to adapt might quickly reduce its efficacy.

"Bacteria are constantly changing their coats so that they can evade the immune system's antibodies."