title: Standoff detection of chemical and biological threats using laser-induced breakdown spectroscopy.
abstract: Laser-induced breakdown spectroscopy (LIBS) is a promising technique for real-time chemical and biological warfare agent detection in the field. We have demonstrated the detection and discrimination of the biological warfare agent surrogates Bacillus subtilis (BG) (2% false negatives, 0% false positives) and ovalbumin (0% false negatives, 1% false positives) at 20 meters using standoff laser-induced breakdown spectroscopy (ST-LIBS) and linear correlation. Unknown interferent samples (not included in the model), samples on different substrates, and mixtures of BG and Arizona road dust have been classified with reasonable success using partial least squares discriminant analysis (PLS-DA). A few of the samples tested such as the soot (not included in the model) and the 25% BG:75% dust mixture resulted in a significant number of false positives or false negatives, respectively. Our preliminary results indicate that while LIBS is able to discriminate biomaterials with similar elemental compositions at standoff distances based on differences in key intensity ratios, further work is needed to reduce the number of false positives/negatives by refining the PLS-DA model to include a sufficient range of material classes and carefully selecting a detection threshold. In addition, we have demonstrated that LIBS can distinguish five different organophosphate nerve agent simulants at 20 meters, despite their similar stoichiometric formulas. Finally, a combined PLS-DA model for chemical, biological, and explosives detection using a single ST-LIBS sensor has been developed in order to demonstrate the potential of standoff LIBS for universal hazardous materials detection.
authors.affiliation: US Army Research Laboratory, AMSRD-ARL-WM-BD, Aberdeen Proving Ground, Maryland 21005-5069, USA. gottfried@arl.army.mil
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Gottfried
authors.forename: Frank C
authors.initials: FC
authors.lastname: De Lucia
authors.forename: Chase A
authors.initials: CA
authors.lastname: Munson
authors.forename: Andrzej W
authors.initials: AW
authors.lastname: Miziolek
mesh_terms: D000391:Air Microbiology; D001412:Bacillus subtilis / Q000302:isolation & purification; D001694:Biological Warfare; D002618:Chemical Warfare; D016002:Discriminant Analysis; D004784:Environmental Monitoring / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D007834:Lasers; D011237:Predictive Value of Tests; D013057:Spectrum Analysis / Q000295:instrumentation / Q000379:methods*