OAK RIDGE, Tenn. -- What's half living, half machine and can sniff out pollutants and chemicals in a single whiff? The latest microsensor technology from the US Department of Energy's Oak Ridge National Laboratory (ORNL) combines living luminescent bacteria with standard semiconductor technology to create a small, inexpensive, diverse air-monitoring sensor.The bioluminescent bioreporter integrated circuit, dubbed "critters on a chip," employs bioluminescent bacteria on a standard chip. The bacteria emit a visible blue-green light when exposed to targeted substances, such as pollutants, explosives and environmental particulates like pollen. Mike Simpson, ORNL research engineer and inventor of the device, said the chip could sense chemical warfare agents or other toxic substances and harmful environmental particles.Advantages of the hybrid chip include compact size, ruggedness, low power requirements and wireless capabilities, according to Simpson. "The bacteria can sense pollutants and organics in places where a standard chip cannot," he said.He added that the circuits could replace bulky, expensive and complicated optical detection systems, which use photomultipliers and buried optical fibers. He also estimated that the chips would cost less than $1 each to mass produce.The hybrid circuit, measuring 2 3 2 3 0.5 mm, can be built using standard integrated circuit manufacturing processes. The biological material Pseudomonas fluorescens HK44 -- taken from a marine bacterium -- is a harmless, genetically engineered micro-organism that produces light as it breaks down hazardous waste. A prototype chip detected naphthalene at concentrations of 2 ppb.