In this paper we describe BioLert II, an ultraviolet laser induced fluorescence (LIF) biological agent monitor for
detecting low concentrations of pathogens amid the ambient aerosol. BioLert II measures the fluorescence intensity and
size of individual particles, and computes the Degree of Threat (DoT), an indicator of the likelihood that a particular
threat material has appeared amid the recently sampled aerosol background. Performance is quantified using Receiver
Operating Characteristic (ROC) curves, which plot the relationship among threat concentration, probability of detection,
and false alert rate. We present BioLert II ROC curves for the detection of several simulated biological agents in an
environment of interest.
Laser-induced fluorescence (LIF) provides a real-time technique for detecting micron-size airborne pathogens. Early LIF biological particle sensors used harmonic generation of UV in solid-state lasers to excite fluorescence. UV diode lasers have several key advantages over traditional lasers: a greater selection of wavelengths for the efficient and selective excitation of specific fluorescent biological compounds; continuous output so that all sampled particles are interrogated; and the ability to combine several UV diode lasers emitting at different wavelengths into a compact multiple-wavelength source for simultaneously exciting several biofluorophores. The coincident detection of multiple biofluorophores is expected to markedly improve discrimination of airborne pathogens from non-biological background aerosols. In this paper, we describe BioLert 2x16C5+1 - a LIF bio-particle sensor with two diode lasers, detection of sixteen fluorescence emission bands bundled into five user-defined linear combinations, and an elastic scatter detector. BioLert 2x16C5+1 also features fluorescence photon counting for sensitivity sufficient to distinguish between single bacterial spores and similar size inert particles, improved signal processing for optimally distinguishing between airborne pathogens and harmless particles, and a highly integrated air sampling system.
Sensors based on laser-induced fluorescence (LIF) enable the rapid detection of micron-size airborne pathogens. As with any sensor, the central design issue is the trade between sensitivity and selectivity. In the case of a LIF bio-particle sensor, the objective is to best distinguish a small concentration of “threat” particles against a potentially much larger concentration of harmless “background” particles, without an excessive rate of falsely alarming when threat particles are absent. In this paper, we characterize sensor performance using four inter-related metrics -- sensitivity, probability of detection, false positive rate (FPR) and response time. We develop several sensor design principles and present a new approach to signal processing called the “degree of threat” algorithm. We describe a recent experiment quantifying the performance of a BioLert testbed in distinguishing a biological agent (Bacillus globigii spores) from a mineral dust (kaolin), using a receiver operating characteristic (ROC) curve to show the trade between sensitivity and FPR.
Laser-induced fluorescence provides a real-time technique for detecting airborne pathogens. Discrimination between biological and non-biological particles can be improved by simultaneously testing for more than one of the several common biofluorophores. Typically, this requires excitation with two or more laser wavelengths, considerably increasing the cost, size and complexity of sensors based on mainframe lasers. Recent advances in UV-emitting AlGaN diode lasers present an opportunity for compact and inexpensive multi-wavelength excitation. In this paper, we will present a model for choosing the best excitation wavelengths and emission bands for discriminating between biological and non-biological particles. We will discuss recent advances in detection, and present fluorescence photon counting experimental results. We will describe techniques for simultaneous excitation and detection at multiple wavelengths to improve selectivity and guard against false positives.
America faces the threat of biological attack. Stopping such attacks requires the fast detection of pathogens. Fluorescence of key biological substances provides a real-time technique for detecting airborne pathogens. Pacific Scientific Instruments has already demonstrated that Bioni, a bio-aerosol sensor based on a CW UV-emitting AlGaN diode laser, can detect within seconds the dispersal of threat organisms in postal sorting facilities and other settings. Minimization of false positives is especially important in bio-threat detection, since false positives can lead to undue public alarm, stoppages of work, and costly clean-ups. Although Bioni has proven itself as a fast and sensitive trigger, its selectivity is limited by its single-wavelength excitation and single-band fluorescence detection. In this paper, we describe the development of BioLert, which uses simultaneous excitation and detection at multiple wavelengths to improve specificity and guard against false positives. Initial experimental results on the detection of individual spores of Bacillus globigii (BG), as well as discrimination against inert aerosols, will be discussed.