Bioaerosol weapons pose a threat to both troops and civilians. Remote detection of bioaerosols is important for timely deployment of effective countermeasures against these weapons and for triggering other detection systems. In this paper we describe a new approach for remote bioaerosol detection based on an eye-safe spectrally broadband backscatter LIDAR. This technique illuminates a remote cloud using a spectrally broadband laser centred about 1.5 μm. The spectrally backscattered fraction of the broadband illumination beam is detected. Using an inverse Monte Carlo algorithm, the particle size distribution and refractive index of the cloud particles can be determined. In this way threat clouds containing anomalous man-made distributions of particles could be discriminated from normal background clouds. The laser is a custom designed source based on a special non-collinear optical parametric oscillator configuration. The laser produces Q-switched pulses with a maximum spectral bandwidth covering the 1.4 to 1.8 μm region. In practice the spectral region of 1.52 to 1.75 μm is used as this matches an atmospheric transmission window. A comparison of this broadband backscatter LIDAR technique, with the commonly used UV lidar fluorescence technique will be presented. Progress to date and details of a prototype LIDAR system will be described.
A novel methodology has been developed for the investigation of bacterial spores. Specifically, this method has been used to probe the spore coat composition of two different Bacillus stearothermophilus variants. This technique may be useful in many applications; most notably, development of novel detection schemes toward potentially harmful bacteria. This method would also be useful as an ancillary environmental monitoring system where sterility is of importance (i.e., food preparation areas as well as invasive and minimally invasive medical applications). This unique detection scheme is based on the near-infrared (NIR) Surface-Enhanced-Raman-
Scattering (SERS) from single, optically trapped, bacterial spores. The SERS spectra of bacterial spores in aqueous media have been measured using SERS substrates based on ~60-nm diameter gold colloids bound to 3-Aminopropyltriethoxysilane derivatized glass. The light from a 787-nm laser diode was used to trap/manipulate as well as simultaneously excite the SERS of an individual bacterial spore. The collected SERS spectra were examined for uniqueness and the applicability of this technique for the strain discrimination of Bacillus stearothermophilus spores. Comparison of normal Raman and SERS spectra reveal not only an enhancement of the normal Raman spectral features but also the appearance of spectral features absent in the normal Raman spectrum.
A novel methodology has been developed for the investigation of bacterial spores. Specifically, this method has been used to probe the spore coat composition of several Bacillus species. This technique may be useful in many applications; most notably, development of novel detection schemes toward potentially harmful biological agents. This method would also be useful as an ancillary environmental monitoring system where sterility is of importance (i.e., food preparation areas as well as invasive and minimally invasive medical applications). This unique detection scheme is based on the near-infrared (NIR) Surface-Enhanced-Raman-Scattering (SERS) from single, optically trapped, bacterial spores. The SERS spectra of several bacterial spores in aqueous media have been measured using SERS substrates based on 60-nm diameter gold colloids bound to 3-Aminopropyltriethoxysilane derivatized glass. The light from a 785-nm laser diode was used to capture/manipulate as well as simultaneously excite the SERS of an individual bacterial spore. The collected SERS spectra were examined for uniqueness and the applicability of this technique for the species identification of bacterial spores.
A novel methodology has been developed for the investigation of bacterial spores. Specifically, this method has been used to probe the spore coat composition of two different Bacillus stearothermophilus variants. This technique may be useful in many applications; most notably, development of novel detection schemes toward potentially harmful bacteria. This method would also be useful as an ancillary environmental monitoring system where sterility is of importance (i.e., food preparation areas as well as invasive and minimally invasive medical applications). This unique detection scheme is based on the near-infrared (NIR) Surface-Enhanced-Raman-Scattering (SERS) from single, optically trapped, bacterial spores. The SERS spectra of bacterial spores in aqueous media have been measured using SERS substrates based on ~60-nm diameter gold colloids bound to 3-Aminopropyltriethoxysilane derivatized glass. The light from a 787-nm laser diode was used to trap/manipulate as well as simultaneously excite the SERS of an individual bacterial spore. The collected SERS spectra were examined for uniqueness and the applicability of this technique for the strain discrimination of Bacillus stearothermophilus spores. Comparison of normal Raman and SERS spectra reveal not only an enhancement of the normal Raman spectral features but also the appearance of spectral features absent in the normal Raman spectrum.
There is a great need for high throughput and sensitive sensors for genetic analysis. These sensors can be used for varied purposes from monitoring gene expression in organims to speciation of possible pathogens. Consequently, an instrument capable of these tasks would be a great benefit for food and water safety, medical diagnostics and defense of military and civilian populations from biological threats. This work examines the development of a hybridization-based biosensor using a novel tapered fiber optic rpobe. The immobilization of single-stranded, synthetic ologinucleotides utilizing aminoproplytriethoxysilane and glutaraldehyde was implemented on the fiber optic sensor. Hybridization takes place with a complementary analyte sequence followed by a fluorescent, labeled signaling probe to form a sandwich assay. Following hybridization, the fiber is interrogated with a diode laser source and the resulting fluorescence signal is detected using a miniature spectrometer.
Current lidar system used for bioaerosol detection utilize either elastic backscatter to detect the presence of any aerosol cloud, or use UV induced fluorescence to detect a potential bioaerosol. We are examining the possibility of using a broad bandwidth (hyperspectral) lidar system to estimate size distributions of aerosol clouds that may possess respirable biological particles. An optical parametric oscillator has been specially designed and fabricated for broad bandwidth operation in the 1.4 to 1.8 micrometer spectral region when pumped with a frequency doubled Nd:YAG laser. We have determined the spectral bandwidth, output, and pumping power characteristics of this device, and we have modeled the feasibility of using this as a source for an aerosol sizing lidar. A novel inverse Monte Carlo (IMC) technique was developed to analyze backscattering data that would result from a lidar system based on this device. Lidar simulation results show that good estimates of size distributions can be extracted for aerosols which have a 1 to 10 micrometer size range even when the signal to noise ratio is only 3:1.
Photothermal interferometry has been demonstrated as a technique that can detect vapors with extremely high sensitivity (parts-per-trillion levels). Our present research uses a photothermal detection scheme that incorporates tunable sources and a modified Jamin interferometric design to provide high selectivity and sensitivity for organo-phosphate vapor detection. Two possible tunable excitation sources are being studied for this sensor technology, a tunable CO2 laser and difference frequency mixing of a tunable NIR laser with a fixed wavelength NIR laser in a nonlinear crystal. The modified Jamin design imparts superior vibrational immunity by ensuring both interferometer beams encounter common optical elements. Examining the two complementary optical outputs of the interferometer, phase shifts on microradian levels have been detected. Trace chemical vapor detection is accomplished by introducing the tunable excitation laser source across the path of one interferometer beam providing a phase shift due to absorptive heating. Preliminary results indicated parts-per-billion level detection of both DMMP and DIMP using ~ 400mW of CO2 laser power at appropriate wavelengths.
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