FLUORESCENCE PARTICLE COUNTER FOR DETECTING AIRBORNE BACTERIA AND OTHER BIOLOGICAL PARTICLES

We have constructed a laser-based particle counter that detects the fl uorescence, as well as the elastic scattering, from individual airborn e particles as they traverse a laser beam. This fluorescence particle counter (FPC) can detect fluorescence from mu m-sized Bacillus subtili s spore agglomerates when illuminated with intense light at 488 nm fro m an argon ion laser, either similar to 0.7 kW cm(-2) extracavity or s imilar to 50 kW cm(-2) intracavity. We suspect that flavins in the spo res are the molecules primarily responsible for the fluorescence, beca use the peak fluorescence emission of the biological materials at this excitation wavelength is in the range 530-550 nm, which is characteri stic of flavins. Fluorescence form kaolin, hematite, and polystyrene p articles was not detectable, the lack of fluorescence indicates that t he FPC may be able to differentiate between biological and nonbiologic al aerosols. The FPC samples aerosol-laden air at a rate of similar to 1 mL s(-1), and is capable of measuring aerosol concentrations up to several thousand per milliliter. The FPC may be helpful in detecting a nd characterizing airborne bacteria and other airborne particles of bi ological origin.