The Fido explosives detector is a battery-powered, handheld sensory device that uses amplifying fluorescent polymer (AFP) materials to detect trace levels of high explosives like trinitrotoluene (TNT). It was developed by Nomadics, a subsidiary of ICX Technologies (now owned by FLIR Systems), in the early 2000s as part of the Defense Advanced Research Projects Agency's (DARPA) Dog's Nose program. The Fido explosives detector is considered the first artificial nose capable of detecting landmines in the real world. The device was named after its ability to detect explosive vapors at concentrations of parts per quadrillion (1 in 10^15), which is comparable to the sensitivity of a bomb-sniffing dog's nose, i.e. the historical "gold standard" for finding concealed explosives.
Overview The Fido explosives detector functions as a trace explosives detector through its use of a specially-made fluorescent polymer film that is extremely sensitive to molecules of TNT, which can be found in more than 85 percent of deployed landmines.
The thin film consists of many repeating chains of amplifying fluorescent polymers that naturally emit visible light when exposed to ultraviolet rays. The fluorescence is the result of excited state electrons (i.e. excitons) travelling down the polymer backbone and between adjacent polymer chains upon absorbing a photon of light. However, the fluorescence reactions become quenched the moment an electron-deficient molecule such as TNT binds to the polymer and traps the migrating exciton at the binding site. A single molecule of TNT is capable of diminishing the fluorescence of entire polymer chains in the thin film, thereby amplifying the effect of a single TNT binding event that may bypass the detection of less-sensitive molecular sensors. The design of the thin film allows the TNT molecules to bind anywhere along the polymer chain, drastically increasing the number of opportunities for the TNT binding event to occur. The amplifying fluorescent polymers used in the Fido explosives detector were engineered to be preferentially responsive to nitroaromatic explosives. The binding of the TNT molecules is believed to be caused by an electrostatic-type interaction between the polymer and the target analyte. Selectivity can also be improved by synthesizing structures into the polymer that are electrostatic mirror images of the desired target analytes. According to reports, there is evidence that the polymers can amplify the quenching of the fluorescence reactions between 100- and 1000-fold compared to conventional quenching mechanisms.
The fluorescent polymer film is coated on the interior surface of the tiny glass tubes that the Fido explosives detector use to draw in air. A blue light-emitting diode (LED) inside the detector serves to excite fluorescent polymer electrons, and the detector's photomultiplier tubes amplifies and reads the wavelength of the emitted light in order to discern whether the light produced by the polymer film had dimmed. The Fido explosives detector provides near real-time, almost instantaneous analysis of the sampled air by registering the intensity of the photomultiplier tubes, which is inversely proportional to the mass of analyte that binds to the polymer films. The polymer films can be exposed repeatedly to samples due to the reversible nature of the binding of the analytes to the film. The Fido explosives detector can return the fluorescence intensity of the polymer films to near the initial baseline reading by drawing in a new flow of clean air to sweep over the polymer film and desorb the analyte.
History The invention of the Fido explosives detector relied heavily on the invention of the amplifying fluorescent polymer (AFP) in the late 1990s. At the time, the use of fluorescent polymers in their solid state was difficult due to their significantly decreased sensitivity and fluorescence compared to polymers in solution. In 1995, chemist Timothy Swager at the Massachusetts Institute of Technology (MIT) was the first to demonstrate the possibility of sensory signal amplification using the molecular wire approach. This technique was later used by Swager to develop AFPs for the first time. Soon afterwards, Swager was awarded a U.S. military research grant to incorporate AFPs into anti-mine technology as part of DARPA's Unexploded Ordnance Detection Program, which was also more informally known as the Dog's Nose program. He licensed the AFP technology to Nomadics and worked with the company to create a prototype of the fluorescent polymers that could be used for explosives detection.
The first field tests of the early prototypes of the Fido explosives detector were conducted in 1999 at Fort Leonard Wood, MO. In 2001, a variant of the Fido explosives detector known as the SeaDog was developed to detect trace amounts of TNT underwater. The SeaDog was then integrated onto an autonomous underwater vehicle (AUV) as part of the U.S. Navy Office of Naval Research's Chemical Sensing in the Marine Environment (CSME) program, becoming the first to demonstrate the mapping of an explosive plume underwater in real time. In 2002, Nomadics was funded by the Strategic Environmental Research and Development Program (SERDP) to configure the Fido explosives detector so that it could be used to monitor explosives contamination of groundwater. The system was further modified and field tested by different organizations within the U.S. Department of Defense, including the U.S. Army Research Laboratory (ARL) and the Night Vision and Electronic Sensors Directorate (NVESD).
The Fido explosives detector was promoted by Nomadics as a low-cost system since most of the hardware, aside from the AFP, consists of commercial off-the-shelf (COTS) electronic and optical components. Unlike most fluorescent quenching explosive sensors, the device did not require solid-state lasers and was not as tightly restrained by thermal stability requirements. In 2003, Nomadics determined that incorporating a two-element array sensor into the Fido explosives detector had the potential to greatly improve the device's ability to discriminate chemical signature compounds from potential chemical interferents without any loss in sensor sensitivity.
By 2004, funding from the Army Research Office (ARO) led to the development of a miniature handheld prototype of the Fido explosives detector that was capable of operating for about six hours on a single rechargeable battery. The production of this system made use of cheaper and more rugged components, such as replacing the photomultiplier with a less sensitive photodiode. These changes resulted in an increase in the noise level that the researchers note would likely not be significant for most applications.
In 2005, Swager and his team found that adjusting the pump power to just over the required threshold for lasing significantly attenuated the lasing emission, resulting in a thirtyfold increase in the sensitivity of Fido explosives detector sensors when the system is operating near the lasing threshold. In the same year, Nomadics marketed a new version of the device known as the Fido XT Explosives Detector, which featured a tethered extension that allowed the sampling head that collected the traces of explosive compounds to be separated from the rest of the device. The XT variant also incorporated a preconcentrator that allowed the device to sample 1000 liters of air at the same time as it would take for the device to sample 1 liter of air without the enhancement. This new addition made it possible for the device to detect the source of the vapor without having the sensor come in physical contact with the contaminated item.
Throughout its continued development, the Fido explosives detector underwent numerous modifications by the U.S. military to be mounted on various types of platforms in order to detect traces of explosive vapors in dangerous environments and hard-to-reach areas. One prominent example was the plan to integrate the Fido explosives detector on robotic platforms in order to remotely detect improvised explosive devices (IEDs). Initially proposed by the then-Assistant Secretary of the Army for Acquisition, Logistics and Technology (ASAALT), the project was spearheaded by the Joint IED Defeat Task Force (JIEDDTF) as part of a 90-day delivery schedule that promised to produce ten integrated systems for soldiers in combat spaces. After much deliberation, iRobot's PackBot was selected as the robotic platform for the Fido explosives detector. However, due to challenges with cost and time restrictions, only half of the proposed ten prototype units were ultimately produced, tested, and fielded in Afghanistan and Iraq. While the fielded prototypes encountered technical problems that hindered performance, repairs by teams of scientists from different Army labs were able to resolve much of the arising issues. Other efforts included the development of Neural Robotics, Inc.'s AutoCopter, which had the detector mounted on a small, unmanned helicopter platform, as well as the integration of the detection system into the Foster-Miller TALON and the U.S. Marine Corps' Dragon Runner.
By 2010, more than 1500 Fido explosives detectors were fielded to American soldiers, and the U.S. Congress provided $7 million in funding to Nomadics to manufacture more Fido explosives detectors for American military operations. In 2011, FLIR Systems (formerly Nomadics) commercially released an upgrade to the Fido XT explosives detector called Fido NXT, which featured a new design for the device to be more durable and modular.
Tests
Fort Leonard Wood Blind field tests for the Fido explosives detector first took place at a DARPA facility at Ft. Leonard Wood, MO in order to evaluate the performance of the device compared to that of trained canines. During the trial, landmines were planted in the test field with two flags approximately 50 cm apart indicating the location of each test position. The landmines were authentic TMA5 or PMA1A landmines with the fuzes and detonators removed along with shipping plugs capping the detonator. Three different teams were tasked with detecting the buried landmines at each test position. One featured the use of the Fido explosives detector and the other two were experienced teams of canines, one trained to detect explosives (i.e. bombs) and the other trained to detect landmines.
According to the results of the field tests, the canine team trained to detect landmines performed better than the canine team trained to detect explosives. The latter eventually withdrew from the field tests due to the immense difficulty in completing the task. However, even the canine team with real-world experience finding landmines faced difficulty performing the task due to very hot and dry weather conditions on the field. In contrast, the team using the Fido explosives detector generally performed better than the experienced canine landmine detection team. In terms of detecting the plastic-cased TMA5 landmines, the best sensor performance demonstrated a detection probability of 89 percent with a 27 percent probability of false alarm. At the conclusion of the field tests, DARPA verified that the performance of the Fido explosives detector was at a level equal to or better than that of the trained canines, marking the first time that an electronic "sniffer" device demonstrated a landmine detection ability comparable to that of trained canines under field conditions.
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