Fluorescence Particle Counter for Detecting Airborne Bacteria and Other Biological Particles

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Abstract
We have constructed a laser-based particle counter that detects the fluorescence, as well as the elastic scattering, from individual airborne particles as they traverse a laser beam. This fluorescence particle counter (FPC) can detect fluorescence from μm-sized Bacillus subtilis spore agglomerates when illuminated with intense light at 488 nm from an argon ion laser, either ∼ 0.7 kW cm−2 extracavity or ∼ 50 kW cm−2 intracavity. We suspect that flavins in the spores are the molecules primarily responsible for the fluorescence, because the peak fluorescence emission of the biological materials at this excitation wavelength is in the range 530–550 nm, which is characteristic of flavins. Fluorescence from kaolin, hematite, and polystyrene particles was not detectable; the lack of fluorescence indicates that the FPC may be able to differentiate between biological and nonbiological aerosols. The FPC samples aerosol-laden air at a rate of ∼ 1 mL s−1, and is capable of measuring aerosol concentrations up to several thousand per milliliter. The FPC may be helpful in detecting and characterizing airborne bacteria and other airborne particles of biological origin.