Timothy Allen Pletcher

Classification and selective collection of individual aerosol particles using laser-induced fluorescence.

We describe the development and performance evaluation of a system for optical interrogation, subsequent selection, and collection of individual aerosol particles entrained in an inlet air stream. Elastic scatter and laser-induced fluorescence obtained from single particles on-the-fly provide compositional information for classification criteria. Individual particles could then be selectively electrically charged and captured to a conductive substrate with an electric potential. The optical subsystem also includes a novel two-beam velocimeter to provide accurate downstream timing. Good overall quantitative performance values are reported for particles in the size range of 1-8 μm at mean rates up to 4 kHz.

Single aerosol particle selection and capture using laser scattering and fluorescence

A dual wavelength UV-LIF fluorescence system that uses 266 nm and 355 nm laser pulses to sequentially excite single aerosol particles has been shown to provide significant discrimination between biological and ambient as well as differentiation among classes of biological particles. This particle classification data can then be used to trigger an electrostatic capture mechanism to deposit individual potential bio-threats particles onto a stainless steel substrate and particles that are not classified as targets are discharged with the exiting airflow. Timing and velocity information for each on-the-fly particle are critical for setting an appropriate delay to capture the particles of interest. A novel CW laser beam technique has been developed to measure the velocity of each particle and initiate a timing sequence. The electrostatic capture mechanism then electrically charges identified particles and produces a time-delayed electric field to drive them into the stainless steel substrate. The resulting collected sample is highly enriched with target, or potential threat, particles in comparison to their percentage in the ambient air. This presentation will describe the unique optical interrogation and diagnostic techniques that have been developed to make this achievement possible, as well as provide the latest system performance results.

Recent advances in the development of a novel aerosol sorting and deposition system for bio-threat sensing applications

Sarnoff Corporation and the Naval Research Laboratory, through support of the U.S. Department of Homeland Security, are developing an automated, high throughput bio-aerosol physical enrichment system designed for use as part of a biological-threat protection system. The Biological Aerosol-Capture-Enrichment (BioACE) system is a bio-aerosol collection system that combines three unique technologies to create physically enriched aerosol samples that can be subsequently interrogated by any number of bio-threat detection systems for the presence of threat agents. An air-to-air concentrator uses an inertial separation technique to highly concentrate an aerosol sample presented to a dual wavelength ultra-violet laser induced fluorescence (UVLIF) optical trigger used to discriminate potential threat particles from non-threat particles conveyed in a collimated particle stream. This particle classification information is used to trigger an electrostatic deposition mechanism to deposit only those particles determined to be potential bio-threats onto a stainless steel substrate. Non-threat particles are discarded with the exiting airflow. The goal for the most recent development effort has been the integration and optimization of these technologies into a unit capable of producing highly enriched particulate samples from ambient air containing variable background aerosol loading and type. Several key technical and engineering challenges were overcome during the course of this development including a unique solution for compensating particle velocity dispersion within the airflow, development of a real-time signal acquisition and detection algorithm for determining material type on a particle by particle basis at rates greater than 2000 particles per second, and the introduction of a robust method for transferring deposited particulate into a 50ul wet sample suitable for most advanced bio-detection techniques. This paper will briefly describe the overall system architecture and then concentrate on the various component and system design tradeoffs required to optimize sample enrichment performance. A system performance model will be presented along with detailed analysis of the optical system components and electronic signal processing needed for achieving high concentration sample enrichment. Experimental methods and data obtained in the laboratory setting and from real world environments will be described and used to support the performance model of the system. Finally, a number of air sampling scenarios will be analyzed using the system performance model to determine the applicability of the BioACE system to the various concepts of operation perceived to be needed for achieving a high performance bio-threat detect-to-protect system.

A study of aerosol particle sorting to provide enriched samples for improved bio-threat analysis

Detection of biological threats in room air is a challenging problem due to their low concentration and the relatively high concentration of background. Dynamic sorting of threat particles from background clutter and dust prior to collection for analysis can provide substantially enriched samples with the advantages of greater analytical accuracy in shorter periods of time. The conceptually simple process of capturing threat particles and rejecting background in fact requires sophisticated particle detection and classification, timing, capture and final threat identification subsystems operating in concert. The effectiveness of the process is also strongly influenced by the operational conditions including threat and background loads as well as the time allotted for sample collection. The requirements of the final threat identification system will dictate the form factor for the collected sample and if collection is to be done dry or into a liquid. A number of sorting systems are currently under development to achieve enrichment for subsequent analysis. Enrichment factors, a common figure of merit for these systems, will be shown to be an inadequate indicator for comparing these systems unless standard operating conditions are used and other parameters are well defined. A set of parameters will be suggested that better allows characterization of the collection component of the sorting system.

Experimental performance of a novel aerosol sorting and deposition system for bio-threat sensing applications

Sarnoff Corporation and the Naval Research Laboratory, through support from HSARPA, are developing an automated, high throughput bio-aerosol physical enrichment system designed for use as part of a biological-threat protection system. The Biological Aerosol-Capture-Enrichment (BioACE) system is a bio-aerosol collection system that combines three unique technologies to create physically enriched aerosol samples that can be subsequently interrogated by any number of bio-threat detection systems for the presence of threat agents. An air-to-air concentrator uses an inertial separation technique to highly concentrate an aerosol sample presented to a dual wavelength ultra-violet laser induced fluorescence (UVLIF) optical trigger used to discriminate potential threat particles from non-threat particles conveyed in a collimated particle stream. This particle classification information is used to trigger an electrostatic deposition mechanism to deposit only those particles determined to be potential bio-threats onto a stainless steel substrate. Non-threat particles are discarded with the exiting airflow. A prototype laboratory system in which particle size dependent elastic scatter rater than fluorescence provides the triggering signal has been experimentally qualified. This paper will present a detailed overview of the prototype system and discuss the physical enrichment results achieved.