In the United States, scientists working at the Sandia National Laboratories, a multimission laboratory operated by Sandia Corporation, a subsidiary of Lockheed Martin Corp., for the US Department of Energy’s National Nuclear Security Administration, have been working on micro size hand-held systems that can detect and analyse gases indicative of chemical, biological and biotoxins and other threats including smuggled humans, for almost 20 years.
Their potential seems unlimited. The military has an ongoing requirement to find low concentrations of chemicals, such as those used in improvised explosive devices (IED) or chemical warfare (CW) agents, before they cause casualties. Soldiers often use detectors in less-than-ideal situations, looking for dangerous substances from among a rich miasma of diesel fumes, smoke and dust.
They need to carry detectors into the field, where instruments must be portable, rugged, reliable and easy to use. In addition, inspectors at checkpoints and border crossings that see large numbers of containers lack automated ways to find trafficked people or contraband.
In the late 1990s, Sandia developed a simple-to-use handheld chemical detector for the military, the MicroChemLab. Since then, Sandia has improved such microfluidics and micro-electro-mechanical (MEMS) systems-based instruments that identify chemicals based on gas chromatography, or GC, and resonator-style instruments such as surface acoustic wave (SAW) detectors. Although SAW-based instruments continue to be important the world of detection needed new devices capable of finding compounds such as carbon dioxide, chemical signals unique to humans or the volatile signatures of pathogens and diseases in livestock and humans.
Ron Manginell led a project to develop such a detector and couple it with GC. Together, they identify vapours by “sniffing” volatile organic compounds (VOCs). The prototype of the new detector, a miniature pulsed-discharge ionization detector, or mini-PDID, is about 1-inch by 1-inch by 2-inches, can be coupled with commercially produced micro-GCs and can run for nine hours on a charge of helium.
Experiments have shown the mini-PDID can detect explosives-related compounds, pesticides and toxic industrial compounds which allowed researchers to look at vapour detection of bacteria, an approach aimed at bringing biological and chemical detection into a small, common platform, Sandia’s research has demonstrated the possibility of a VOC-based detector for humans as part of the project. Current commercial detectors to find human cargo are about the size of a large shoebox, minus the electronics that operate them.
The micro-GC system can filter out common interfering agents such as water in the form of humidity, and detected compounds at sub-parts per billion concentrations in 6 seconds to 2 minutes in lab and field tests. Sandia’s micro-GC system approach is more compact and faster than commercial GC units and can be operated by non-experts. It eliminates the need for a mass spectrometer, which detects chemicals by measuring the relative concentrations of atoms and molecules. Eliminating a mass spectrometer removes the need for vacuum pumps, which are too big and costly for broad field use.
“Systems based on the same body of research are being used to analyse water quality and could be used to monitor diseases by just “smelling” a patient’s breath,” said Manginell.
Initial support for developing the micro-GC system came from Sandia’s Laboratory Directed Research and Development programme with additional funding from the DOE, Defense Advanced Research Projects Agency and DTRA. However, Manginell also said that the technology needs engineering innovations, such as a tiny low-volume, high-flow-rate valve that can operate under high pressure. In addition, researchers are looking for funding to further develop the mini-PDID and make it even smaller. Manginell wants to reduce the housing to the size of an AAA battery, and ultimately to MEMS size, typically devices measuring between 20 micrometers to a millimeter. For comparison, a human hair averages 70 microns in diameter.
In general, Sandia’s chemical detection instruments work by collecting and concentrating a sample of air, separating the chemicals using a GC and finding the targeted ones through selective detection. The micro-GC system can filter out common interfering agents such as water in the form of humidity, and detected compounds at sub-parts per billion concentrations in 6 seconds to 2 minutes in laboratory and field tests.
The Sandia micro-GC technology is also being used in the Rhizosphere Observations Optimizing Terrestrial Sequestration (ROOTS) project sponsored by the US Department of Energy’s Advanced Research Project Agency-Energy in 2017. Sandia National Laboratories has received $2.4 million to adapt previously developed sensors to monitor root function and plant health in new, noninvasive ways. For the ROOTS programme, researchers will use the micro-GC system to detect signals from environmental stress, such as drought, heat and nutrients, and biological stress, such as insect and pathogen attacks, as well as assess root growth. According to Ron Manginell, by placing very thin sample collection spikes in the ground and using the cutting-edge micro-GC detectors, the researchers plan to monitor normal plant VOCs and their stress signals in almost real-time.