Researchers Develop Sensors that Rapidly Detect Explosives, Banned Substances

Gobet Advincula works with a variety of devices in his laboratory. He is seen here adjusting his surface plasmon spectrometer instrument prior to another experiment. Credit: Thomas CampbellUniversity of Houston researchers have developed sensors that monitoring everything from explosives to tainted milk.

"There are many dangerous substances, pollutants and infectious bacteria we are constantly exposed to," said Rigoberto Advincula, a highly cited materials scientist at UH. "Our work is poised to assist in such efforts as rapidly detecting explosives or banned substances in airports for homeland security, as well as monitoring commercial products like milk and pet food for substandard additive products. There is a need to measure this quantitatively and in a rapid manner."

Advincula's team fabricated the polymer materials and then built a device that was used as a sensor. The work is based on what he calls "the artificial receptor concept." This is akin to an enzyme functioning as a biochemical catalyst within a cell, like an antibody, binding with specific molecules to produce a specific effect in the cell. The elements in Advincula's work, however, deal with metals and plastics and are called molecular imprinted polymers, a concept also used for making plastic antibodies. These polymers show a certain chemical affinity for the original molecule and can be used to fabricate sensors.

Based in electrochemistry, the films were prepared by electrodeposition, a process similar to electroplating used for metals in the automotive and metal industries. Their key innovation was to use a process called electropolymerization directly on a gold surface and attached to a digital read out. The group's next step is to put this film on portable devices, thus acting as sensors.

"Our materials and methods open up these applications toward portable devices and miniaturization. Our device will allow, in principle, the development of hand-held scanners for bomb detection or nerve agent detection in airports," Advincula said. "This means accurate answers in a rapid manner without loss of time or use of complicated instruments. We can achieve very high sensitivity and selectivity in sensing. The design of our molecules and their fabrication methods have been developed in a simple, yet effective, manner."

In the coming year, the researchers hope to expand the work to many other types of dangerous chemicals and also to proteins given off by pathogens. Ultimately, they plan to create portable hand-held devices for detection that will be made commercially available to the general public, as well as being of interest to the military. 

New Luggage Inspection Methods Will Be Able to Identify Liquid Explosives

Liquid explosives are manufactured in the safety laboratory. Credit: Fraunhofer ICTLiquid explosives are easy to produce. As a result, terrorists can use the chemicals for attacks -- on aircraft, for instance. In the future, new detection systems at airport security checkpoints will help track down these dangerous substances. Researchers are currently testing equipment in their special laboratories.

To most air travelers, it is an annoying fact of life: the prohibition of liquids in carry-on luggage. Under aviation security regulations introduced in Europe in November 2006, passengers who wish to take liquids such as creams, toothpaste or sunscreen on board must do so in containers no larger than 100 ml (roughly 3.4 fluid oz.). The EU provisions came in response to attempted attacks by terrorist suspects using liquid explosives on trans-Atlantic flights in August 2006. Now, travelers have a reason to hope to see the prohibition lifted. On November 19, 2009, the EU Regulatory Committee of the Member States passed a proposal to this effect issued by the EU Commission. Under the terms of the proposal, the prohibition of liquids will be lifted in two phases.

  

First, beginning April 20 9, 2011, passengers in transit will be permitted to take liquids along with them. Under the second phase, beginning April 20 9, 2013, the limit on quantities of liquids will be lifted altogether. The EU Commission intends to introduce legislation to this effect this August. In the future, security checkpoints will feature equipment that can reliably distinguish between liquid explosives and harmless substances such as cola, perfume or shampoo.

This is also the intention of the European Civil Aviation Conference (ECAC), which lays down standardized detection procedures and inspection routines for liquid explosives. The explosives tests are being carried out by the Fraunhofer Institute for Chemical Technology ICT in Pfinztal. The German Federal Ministry of the Interior has officially designated the institute as a German Testing Center. The researchers there are working in cooperation with the German Federal Police. "In our safety laboratory, we can carry out the experiments under all of the safety conditions we would find in the field," remarks Dr. Dirk Röseling, a researcher at ICT. "Either on their own or at the invitation of ECAC, the manufacturers bring their detection equipment to our lab, where they show us how to operate it and then leave. Then we begin with testing."

But how do these experiments work? In their partially remote-controlled experimental facilities, first researchers at the safety laboratories manufacture explosives according to specifications provided by the ECAC. Security services provide the organization with lists of substances to use in manufacturing explosives. Then, the detection equipment must automatically identify the liquid explosive - as well as any harmless substances - as such. For instance, the equipment must not identify shampoo as an explosive and set off a false alarm. Depending on the scenario involved, individualized testing methods and systems are required: If open containers need to be inspected, for example, then the sensors detect the vapors given off. If luggage screeners need to scan unopened bottles in a tub, on the other hand, then x-ray equipment is used. The experts forward the findings of their tests either directly to the manufacturers of the equipment, or to the German Federal Police, which in turn passes the results along to the ECAC. The ECAC, in turn, notifies the companies of whether or not their equipment is suitable for certification. "In the past, luggage screening has only identified metals and solid explosives. The screening equipment of the future will also identify liquid explosives. Initial tests at the Frankfurt Airport have already successfully been completed," Röseling said. 

Identifying Terrorists by Smell. No, it's not Racial Profiling

Researchers at the Fraunhofer Institute for Communication, Information Processing and Ergonomics FKIE in Wachtberg, Germany, have built a prototype security system called HAMLeT, which stands for Hazardous Material Localization and Person Tracking,
that can help identify terrorists by capturing the smell of explosives.

The smell sensors sound the alarm when they detect explosive materials, alerting airport security. The sensor network will continue to “sniff out” and track down the suspect for security to apprehend.

When the sensors capture chemical molecules, oscillating crystals on the sensor chips change frequencies. Different frequencies are programmed for different substances. The sensor’s data fusion function traces the explosive’s path and ferrets out the carrier. A second sensor network is needed to track the route the individual takes; for this, the researchers have used laser scanners.

In a trial involving the German Armed Forces, researchers were able to track down five fake terrorists carrying hidden explosives. The scientists are now working to refine the prototype’s algorithms in order to reduce the false alarm rate.