With the recent anthrax attacks in the US, finding a means of detecting airborne biological agents from a safe distance has become all the more important. Fourier transform infrared (FTIR) spectroscopy may be a solution, suggests a new study.A number of research teams have investigated the ability of infrared methods to detect and identify harmful bio-aerosols, but the viability of these techniques is a matter of debate. Kristan P. Gurton and his colleagues at the US Army's Harry Diamond Laboratories in Adelphi, Md., suggest that researchers must study well-characterized bio-aerosols to better understand the potential of infrared detection techniques.Gurton's team has measured the infrared spectral extinction of aerosolized Bacillus subtilis var. niger endospores, a common simulant for biological warfare agents, using a Bomem DA2.02 FTIR spectrometer at 3 to 13 µm. While it is not yet possible to conclude that the technique can detect and identify harmful bio-aerosols from a safe distance, the initial study made a few things clear.Low-resolution spectroscopy can detect bio-aerosols, because they display relatively smooth extinction spectra, but 10 to 20 particles per cubic centimeter of the bio-aerosol must be present. The minimum particle density increases sharply when certain factors are considered, such as spectral masking – attributable to path radiance and to molecular absorption by gaseous CO2, H2O and O2 – and the distance between the spectrometer and the endospore cloud.The researchers believe that any infrared analysis will be limited to active illumination techniques, in which the light source is powerful enough to mitigate the effects of these factors.