The detection of aerosols within fluid samples can be accomplished by optical methods. Such methods are useful in detecting potentially harmful aerosols such as biological aerosols that may be present after a biological agent attack or industrial accident. It is well known that biological molecules fluoresce when excited by ultraviolet (UV) radiation. As a result, biological molecules in an aerosol sample can be optically detected by irradiating the sample with ultraviolet radiation and observing the fluorescence response. Since differing excitation wavelengths may be used to detect different classes of biological molecules, the excitation wavelength can be chosen to detect specific classes of biological molecules such as proteins, flavinoids, and metabolite products.
A biological aerosol detector was developed that includes an optical excitation source having a primary emission band and a secondary emission band. The excitation source can be a semiconductor ultraviolet optical source with a primary emission band in the ultraviolet spectrum and a secondary emission band at longer wavelengths. The primary emission band is configured to excite biological molecules in an aerosol sample in the detector’s optical cavity. Filtering optics are included to attenuate radiation that is emitted in the secondary emission band that, when scattered, can mimic the fluorescence response of a biological molecule.
The filtering optics can include a dichroic mirror configured to reflect radiation in one of the emission bands, and to transmit radiation in the other. A focusing optic, such as a ball lens, can be positioned in the optical path between the excitation source and the dichroic mirror. The filtering optics can include an optical filter positioned in the optical path between the dichroic mirror and the optical cavity to attenuate the intensity of radiation in the secondary emission band. The filtering optics can also include a lens positioned in the optical path between the dichroic mirror and the optical filter. An orifice, located in a housing that encloses the optical cavity, can be configured as a control aperture to limit stray radiation from entering the optical cavity. The orifice can be made of any material with a UV-absorbing coating, e.g., graphite.
The detector also can include an optical excitation source, an optical cavity in which a sampled aerosol is irradiated by the optical excitation source, a housing that encloses the optical cavity, and a combined intake and exhaust gas manifold that passes through the housing and into the optical cavity. The manifold can collect an aerosol sample and direct it into the optical cavity, and can exhaust the aerosol sample from the optical cavity after it has been irradiated by the optical excitation source. The sampling, transport, and exhaust of the aerosol can occur in the same plane to increase the time the aerosol is irradiated by the excitation source.