A proposed compact, portable instrument would sample micron-sized airborne particles, would discriminate between biological ones (e.g., bacteria) and nonbiological ones (e.g., dust particles), and would collect the detected biological particles for further analysis. The instrument is intended to satisfy a growing need for means of rapid, inexpensive collection of bioaerosols in a variety of indoor and outdoor settings. Purposes that could be served by such collection include detecting airborne pathogens inside buildings and their ventilation systems, measuring concentrations of airborne biological contaminants around municipal waste-processing facilities, monitoring airborne effluents from suspected biowarfare facilities, and warning of the presence of airborne biowarfare agents.
The instrument would be based partly on a conventional aerosol-particle counter and partly on a fluorescence subsystem for identifying biological particles. Aerosol particles would be drawn through a series of aerodynamic lenses (nozzles sized and shaped to focus variously sized particles into a narrow stream). The lenses would be designed so that only respirable particles would end up in a narrow outlet stream flowing across the optical path of a pulsed ultraviolet laser in the fluorescence-based subsystem. Before reaching the optical path of the pulsed ultraviolet laser, the aerosol particles would cross the beam of a continuous-wave semiconductor diode laserthat would be used to size the particles. If the size of an individual particle was found to be within a certain range, the ultraviolet laser would be triggered to fire as the particle crossed its path, thereby dramatically reducing power requirements for autonomous operation.
The pulse of ultraviolet light would excite fluorescence in the particle. The fluorescent light would be collected and split into three separate spectral bands by use of lenses, dichroic filters, and band-pass filters. The outputs of photodetectors for the three spectral bands would be processed to determine whether the particle could be of biological origin. The indication of a possible biological particle would cause an aerosol-sampling module to be turned on to collect particles on a solid substrate. The substrate would be placed under an automated microscope equipped with a video camera, the output of which would be digitized and processed by image-analysis software to identify the collected particles.
This work was done by Steve Savoy and Mike Mayo of Nanohmics, Inc. for Marshall Space Flight Center. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Bio-Medical category. MFS-32081-1