A highly sensitive trigger allows rapid detection of biological agents

The Rapid Agent Aerosol Detector was photographed with a 12-inch ruler to represent the scale. Credit: by researchers

The Agent Aerosol Detector developed at Lincoln Laboratory has shown excellent performance accuracy in identifying toxic biological particles suspended in the air.

Any space, closed or open, can be vulnerable to the dispersal of harmful biological agents in the air. Silent and almost invisible, these bioagents can make or kill living things before measures can be taken to mitigate the effects of the bioagents. Crowded places are the main targets for two war attacks designed by terrorists, but field or forest expanses can be the victim of an air bioattack. Early warning of suspected biological aerosols can accelerate corrective responses against releases of biological agents; the sooner the cleaning and treatment is started, the better the affected sites and people will have a better result.

WITH ONE Researchers at Lincoln Laboratory have developed a highly sensitive and reliable agent for the U.S. military’s early warning system for biological warfare agents.

“The trigger is a key mechanism in a detection system because continuous monitoring of the air in the location collects aerosolized particles that can pose a threatening threat,” says Shane Tysk, principal investigator of the laboratory’s bioaerosol launcher, Rapid. Agent Aerosol Detector (RAAD), and member of the technical staff of the Advanced Materials and Microsystems Group in the laboratory.

The initiator informs the detection system to collect particle grains and then initiate the process of identifying the particles as potentially dangerous bioactives. RAAD has been shown to have a significant reduction in false positive rates, while maintaining a detection performance that matches or exceeds the best systems currently in place. In addition, early tests have shown that RAAD has significantly improved reliability compared to currently installed systems.

RAAD system

This illustration of the RAAD system shows the different modules mounted on the outside of the system for easy maintenance or replacement access. Credit: by researchers


The RAAD determines the presence of biological warfare agents through several stages. First, aerosols are introduced into the detector by a combined agency of an aerosol cyclone that uses high-speed rotation to extract small particles and an aerodynamic lens that condenses (i.e., enriches) the volume of small particles into a beam. aerosol. The RAAD aerodynamic lens is more efficient than any other concentrator that enriches the air.

The near-infrared (NIR) laser diode then creates a structured trigger structure that detects the presence, size, and trajectory of each aerosol particle. If the particle is large enough to damage the respiratory tract – approximately 1-10 micrometers – a 266 nanometer ultraviolet (UV) laser is activated to illuminate the particle, and collects fluorescence caused by a multi-band laser.

The detection process continues as an embedded logic decision, called a “trigger spectrum,” that uses the scattering of NIR light and UV fluorescence data to predict that the particle composition matches that of a bioagent similar to the threat. “Particles appear to be a kind of threat, spark-induced fault spectroscopy is enabled to characterize the elemental content of the particle to evaporate particles and collect atomic emissions,” says Tysk.

Spark-induced fault spectroscopy is the final stage of measurement. This spectroscopy system measures the basic content of the particle and its measurements lead to the creation of a high temperature. plasma, evaporation of the aerosol particle, and measurement of the atomic emission from the thermally excited states of the aerosol.

The measurement phases – a structured trigger range, UV-excited fluorescence and spark-induced fault spectroscopy – are integrated into a step-by-step system that provides seven measurements for each particle of interest. From the hundreds of particles that enter the measurement process every second, a small subset of particles is selected for measurement in three stages. The RAAD algorithm searches the data stream for changes in the temporal and spectral characteristics of the particle set. If a sufficient number of threatening particles is found, the RAAD alerts the aerosol to say that there is a biological threat.

Advantages of TABLE design

“Since RAAD operates 24 hours a day, seven days a week, we have incorporated a variety of features and technologies to improve system reliability and make it easier to maintain RAAD,” says Brad Perkins of the RAAD development team. For example, Perkins goes on to explain that the entire air treatment unit is a module mounted on the outside of the RAAD to facilitate the service of items that need to be replaced, such as filters, air-to-air concentrators, and pumps that wear out with use.

To improve the reliability of the detection, the RAAD team chose to use carbon filtered, HEPA filtered and dehumidified coating air and purge air (compressed air that expels external gases) around optical components. This approach allows outdoor air pollutants not to accumulate on the optical surfaces of the RAAD, which can reduce sensitivity or false alarms.

RAAD has spent more than 16,000 hours in field trials, while at the same time showing a very low rate of false alarms, unprecedented for a biological trigger with a high level of sensitivity. “What sets RAAD apart from competitors is the number, variety and fidelity of measurements made for each aerosol particle,” says Tysk. As these individual measurements of aerosol particles pass through the system, the trigger allows the biological warfare agent to be separated from the ambient air at high speed. Since the RAAD does not designate the particular bioagent detected, further laboratory testing of the sample should be performed to determine its exact identity.

The RAAD was developed with the support of the Defense Threat Reduction Agency and the Directorate General of the CBRN Joint Defense Program. The technology is transitioning from Lincoln Laboratory production to Chemring Sensors and the Electronic System.

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