A SMALL radio-controlled aircraft could soon be monitoring the air for signs of biological weapons. Fitted with a sensor developed at the Naval Research Laboratory (NRL) in Washington DC, the craft will venture into possible danger zones and send back data on any biowar bacteria it detects.

The biosensor was conceived by a team led by Frances Ligler of the NRL. Its development was funded by the Defense Advanced Research Projects Agency, part of the US Department of Defense.

To carry its sensor into the danger zone, the NRL researchers mounted it in a 19-kilogram radio-controlled aircraft with a wingspan of about 4 metres. "They're remote controlled, like little toy planes," says Ligler. "They're cheap and they fly low, which is where you need to be."

When the plane is in flight, air is forced into an on-board sampling chamber where it creates a vortex in a pool of water. Micrometre-sized particles wash out of the air and into the water. "It takes no power to run it," Ligler says.

Every five minutes, water from the chamber is pumped over the sensor, which consists of four optical fibres, each with a tapered probe fixed to its core (see Diagram). The probe is coated with an antibody to the spores of a particular bioweapon bacterium. If the bacterium is present in the water, it binds to the antibody. Each probe can be used to detect a different bacterium.

The sensor is then bathed in a solution containing a second set of fluorescent antibodies. These are designed to bind to different sites on any target bacteria that are already attached to the probes, creating a sandwich-like structure. When a fluorescent antibody has bound to the bacterium it seeks, it sends light down the optical fibre, where it can be detected by a photodiode to generate an electronic signal.

Repeated sampling allows bacteria to accumulate on the probes. Even if the concentration of bacteria in the air is initially too low to pr
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Contact: Claire Bowles
claire.bowles@rbi.co.uk
44-171-331-2751
New Scientist
9-Sep-1998