By Mark Ward
Technology correspondent, BBC News website
Tiny particles of gold could soon be helping to spot viruses, bacteria and toxins used by bio-terrorists.
Chemistry helps spot many different toxins in seconds
Researchers in the UK have found that gold nanoparticles are very effective detectors of biological toxins.
The particles reveal the presence of poisons far faster than existing techniques which often involve shipping samples back to a lab.
The aim is to integrate the technology in a portable device that could give instant answers at crime scenes.
Led by Professor David Russell, researchers at the University of East Anglia are studying ways to use the nanoparticles as a detector of dangerous biological substances.
The research makes use of gold nanoparticles that are only 16 nanometres in diameter - roughly 1/5000th the width of a human hair.
Earlier work by Professor Russell's team has refined manufacturing methods so relatively large amounts of the particles can be made quickly.
Once made, the particles are coated with sugars tailored to detect different biological substances.
When mixed with a weak solution of the sugar-coated nanoparticles, the target substance, be it a poison such as ricin or a bug like E.coli, binds to the sugar. This changes the properties of the solution and makes it change colour.
Professor Russell said pure solutions of the gold nanoparticles are a strong red colour but instantly change to blue when the target substance is present.
He said work had been done with solutions of particles tailored for just one toxin as well as mixtures that combined nanoparticles tailored to spot different substances.
The scientist said colour changes were less dramatic with mixtures of nanoparticles but were still significant enough to easily spot. The extent of the colour change can also reveal how much of particular toxins were present.
"We can get quantitative information about how much of a toxin is present," said Professor Russell.
This could be useful, he said, if the detection system is being used to check for impurities in water as it would reveal if they are present in small enough amounts to be safe or have passed a threshold level.
The nanoparticles can spot if water is clean enough to drink
"We can detect well below the threshold limit so we know the water is pure before we drink it," he said.
Future research will focus on building the detection system into a portable device that can be taken out to places where poisonous substances are thought to be present.
Such a gadget would give basic information about which toxins were present and in what quantities. Professor Russell speculated that the portable detector could be ready in five years time.
The research team is also looking into ways of using the detection system to help scene of crime officers analyse biological fluids such as sweat that criminals leave behind.
"There's a lot of chemical information in there," said Professor Russell.
The early results of Professor Russell's work were presented at a conference in London organised by the Engineering and Physical Sciences Research Council (EPSRC) which showcased research that aims to help forensic scientists.