Measurement of biological aerosol with a fluorescent aerodynamic particle sizer (FLAPS): Correlation of optical data with biological data

Biological aerosol measurement in real time is an urgent military requirement that also has many potential nonmilitary applications. Such detection capabilities will be useful in environmental monitoring, for example, in gathering information in perceived hazardous areas like housing developments downwind of sewage treatment plants. Experience gained from measuring fluorescence signals of single bacterial spores under flow cytometry using UV excitation at 340-360 nm, was applied to concept testing of a prototype instrument, built to do the same for aerosols. This machine was capable of resolving particle size as well as fluorescence intensity of each particle under laboratory and field conditions; it was called the fluorescent aerodynamic particle sizer (FLAPS). A second generation FLAPS (FLAPS2) was designed to be smaller, power efficient and field portable. FLAPS2 was challenged under refereed conditions in blind trials to determine if it could detect biological aerosols in natural field environment. This paper describes practical aspects of measuring biological aerosols when the results must be compared to reference samplers that provide culturable or 'live' data. Treatment of particle size and fluorescence information is discussed with respect to FLAPS and reference data fidelity. Finally, an objective method is introduced to evaluate FLAPS data correlation to reference data. The measurements suggest that there is positive correlation between FLAPS measurements and live biological aerosol particles.