MEDFORD, Mass. -- One of the most complex sensors of all -- the human nose -- is the inspiration for a fiber optic sensor that can detect and differentiate chemical vapors better than commercial electronic chemical-detecting devices."Commercial 'electronic noses' don't even come close to what a real nose can do," said David Walt, a Tufts University chemistry professor and project leader of the research team developing the new sensor. The team's optical "artificial nose" would be capable of not only detecting and identifying very small amounts of chemical vapor, but also differentiating individual chemicals in complex mixtures -- something that electronic detection devices thus far have not been able to do."The concentrations that we are able to detect (with the optical sensor) are on the same order of magnitude as what commercial sensors can," explained Walt. "Since electronic sensors do not have the information density of our optical sensor, they have not been able to identify individual chemicals. They can tell if a material is within a range of acceptability, but they cannot differentiate or isolate individual compounds." The optical system's array of polymer-coated fibers -- analogous to a human nose's olfactory receptor cells -- is exposed to various chemical vapors precisely pumped by an automatic delivery system, simulating a "sniffing" action. A xenon arc lamp with a standard bandpass filter sends light at 535 nm through the fiber. When exposed to the vapors, the polymers fluoresce at 610 nm, and the signal from each fiber travels through the bundle to a CCD camera. The system collects and compares the sequence of images, or response profiles, and stores the data in its "neural network," so when the "nose" comes in contact with the vapor again, the network recognizes the pattern and can remember the chemical.The team will be using the system in medical, environmental, chemical-process-control and food-quality applications. For now, however, the researchers are not pursuing specific commercial ventures until they are convinced they have come as close as they can to creating a counterpart to the human nose, which is not expected for another five to 10 years. "We have a long way to go," acknowledges Walt. "We're learning as we go. The natural system is truly driving the work."