Friday, 19 July 2013



                        DETECTING OF BOMBS 




                     Moses dhilip kumar





                              “ Bomb sniffing dogs today, nanotechnology tomorrow”

                             The challenges in transportation security, most notably air transport, evolve around detecting explosives before they reach their target, i.e. get on a plane for instance. The two technology-based methods of explosive detection are either nuclear-based (probing the screened object with highly penetrating radiation) or rely on trace detection. Trace detection techniques use separation and detection technologies, such as mass spectrometry, gas chromatography, chemical luminescence, or ion mobility spectrometry, to measure the chemical properties of vapor or particulate matter collected from passengers or luggage. All these methods require bulky and expensive equipment, costing hundreds of thousands of dollars apiece. This results in a situation where the effort and technology involved in the detection of explosives are orders of magnitude more expensive than the effort and costs incurred by terrorists in their deployment. Today, the cheapest, very reliable, and most mobile form of explosive detection is decidedly low-tech - dogs. The olfactory ability of dogs is sensitive enough to detect trace amounts of many compounds, which makes them very effective in screening objects. A dog can search an entire airport in a couple of hours. Using a chemical analysis machine would mean wiping down nearly every surface in the airport with a sterile cotton pad, then sticking those pads, one by one, into a computer for analysis. Given the recent advances of nanotechnology, researchers are now trying to develop the next generation of explosives sensors that are accurate, fast, portable and inexpensive – and don't need to be fed. In contrast to the currently used machines, dogs have the advantage of being relatively uncomplicated. "The [chemical analysis machines] that are used as an alternative to dogs are just extremely, unbelievably advanced and complex," says Rick Charles, an expert on aviation security at Georgia State University. "They involve things like ion mobility spectrometry – processes that literally do a molecular analysis of the contents of the container." The average bomb-sniffing dog may pee on a suitcase, but at least he won't lose his ability to sniff if someone bumps into him the wrong way. (quoted from an article in Salon "On the prowl with the secret bomb dogs")




                             The challenge of detecting explosives on people or objects is considerable: often there are only minute quantities available; there is a broad range of effective explosives that need to be screened for; all current detection technologies, including dogs, require close proximity to the person, package, or vehicle being screened. Among the major detection techniques, trace detection suffers from the fact that available vapor plumes are normally too dilute for detection at a distance. Another major drawback is that current explosives sensors are bulky and expensive and cannot be miniaturized (think of the screening gates at airports). Furthermore, the effectiveness of chemical trace analysis is highly dependent on three distinct              steps:

(1) sample collection,

(2) sample analysis, and

(3) comparison of results

 with known standards. If any of these steps is suboptimal, the test may fail to detect explosives that are present. These issues set the parameters for the design and development of nanotechnology-based, next generation bomb sniffing equipment. The goal in developing nanotechnology enabled sensors is to achieve reliable, extremely sensitive and inexpensive sensors (at least a thousand times cheaper than today's equipment) that can be mass produced and deployed in large enough numbers so that the cost of detection by law enforcement will be less than the cost of deployment by terrorists.







                            One example of a next-generation nanotechnology explosives detector is a nanocomposite film that shows very fast fluorescence response to trace vapors of explosives such as TNT, DNT or NB. Developed by researchers in China, a silica film doped with nitrogen-containing macrocyclic molecules - porphyrins - shows a fluorescent response to even trace levels of explosives such as TNT .

Two key features of these mesostructured films, namely the porous structure and the large surface area, are believed to be principally responsible for the observed remarkable sensing performance.


                            SEM image of floppy diskette with traces of C-4 explosive

                                        PREPARATION OF NANOMATERIALS




The unique mesoporous structure provides a necessary condition for the facile diffusion of analytes to sensing elements, while the large surface area considerably enhances the interaction sites between analyte molecules and sensing elements, and thereby further improves the detection sensitivity.

 "Since the preparation is very easy, the used materials are inexpensive, organic sensing elements become stable enough in the inorganic matrix, and the synthesized sensing films are easily incorporated into inexpensive and portable electronic devices, this explored method should be a promising alternative to other developed explosive detection methods" says Guangtao Li from the Key Laboratory of Organic Optoelectronics & Molecular Engineering of the Ministry of Education at Tsinghua University, Beijing. Another chemical sensor approach is based on carbon nanotubes (CNTs). Developed at the NASA Ames Research Center, this platform provides an array of sensing elements where each sensor in the array consists of a CNT and an interdigitated electrode as a transducer. Due to the interaction between nanotube devices and gas molecules, the electron configuration is changed in the nanostructured sensing device, therefore, the changes in the electronic signal such as current or voltage can be observed. By measuring the conductivity change of the CNT device, the concentration of the chemical species, such as a certain type of molecule, can be measured.

Combined with MEMS technology, light weight and compact size sensors can be made in wafer scale with low cost. T nanosensor technology can extend its application in civilian areas such as explosives detection, monitoring filter bed breakthroughs, personnel badge detectors, embedded suit hermiticity sensors, and other applications. Additionally, a wireless capability with the sensor chip can be used for networked mobile and fixed-site detection and warning systems for military bases, facilities and battlefield areas.

Portable, cheap and fast explosives detector built with nanotechnology :

 Due to the the increased use of modern bombs in terrorist attacks worldwide, where the amount of metal used is becoming very small, the development of a new approach capable of rapidly and cost-efficiently detecting volatile chemical emission from explosives is highly desirable and urgently necessary nowadays.
The trained dogs and physical methods such as gas chromatography coupled to a mass spectrometer, nuclear quadrupole resonance, electron capture detection as well as electrochemical approaches are highly sensitive and selective, but some of these techniques are expensive and others are not easily fielded in a small, low-power package. As a complementary method, however, chemical sensors provide new approaches to the rapid detection of ultra-trace analytes from explosives, and can be easily incorporated into inexpensive and portable microelectronic devices.                                   
 In comparison to conjugated-polymer based sensors, the fabrication of these hybrid films is very simple, the used materials are inexpensive, and the trapped organic sensing elements also become very stable in the inert silica matrix." Two key features of these mesostructured films, namely the porous structure and the large surface area, are believed to be principally responsible for the observed remarkable sensing performance. The unique mesoporous structure provides a necessary condition for the facile diffusion of analytes to sensing elements, while the large surface area considerably enhances the interaction sites between analyte molecules and sensing elements, and thereby further improves the detection sensitivity.                                        
                                                                            OLD METHOD


                                                                        NEW NANOMETHOD
                         This is the most important component in this nano detecting device
Other projected products most commonly involve using nanosensors to build smaller integrated circuits, as well as incorporating them into various other commodities made using other forms of nanotechnology for use in a variety of situations including transportation, communication, improvements in structural integrity, and robotics. Nanosensors may also eventually be valuable as more accurate monitors of material states for use in systems where size and weight are constrained, such as in satellites and other aeronautic machines.
Existing nanosensors
Currently, the most common mass-produced functioning nanosensors exist in the biological world as natural receptors of outside stimulation. For instance, sense of smell, especially in animals in which it is particularly strong, such as dogs, functions using receptors that sense nanosized molecules. Certain plants, too, use nanosensors to detect sunlight; various fish use nanosensors to detect minuscule vibrations in the surrounding water; and many insects detect sex pheromones using nanosensors.
Chemical sensors, too, have been built using nanotubes to detect various properties of gaseous molecules. Carbon nanotubes have been used to sense ionization of gaseous molecules while nanotubes made out of titanium have been employed to detect atmospheric concentrations of hydrogen at the molecular level. Many of these involve a system by which nanosensors are built to have a specific pocket for another molecule. When that particular molecule, and only that specific molecule, fits into the nanosensor, and light is shone upon the nanosensor, it will reflect different wavelengths of light and, thus, be a different color

 Production methods of nanosensors:
There are currently several hypothesized ways to produce nanosensors. Top-down lithography is the manner in which most integrated circuits are now made. It involves starting out with a larger block of some material and carving out the desired form. These carved out devices, notably put to use in specific microelectromechanical systems used as microsensors, generally only reach the micro size, but the most recent of these have begun to incorporate nanosized components.
Another way to produce nanosensors is through the bottom-up method, which involves assembling the sensors out of even more minuscule components, most likely individual atoms or molecules. This would involve moving atoms of a particular substance one by one into particular positions which, though it has been achieved in laboratory tests using tools such as atomic force microscopes, is still a significant difficulty, especially to do en masse, both for logistic reasons as well as economic ones. Most likely, this process would be used mainly for building starter molecules for self-assembling sensors.
                                                       SIZE OF NANOSENSOR
(A) An example of a DNA molecule used as a starter for larger self-assembly. (B) An atomic force microscope image of a self-assembled DNA nanogrid. Individual DNA tiles self-assemble into a highly ordered periodic two-dimensional DNA nanogrid.

The third way, which promises far faster results, involves self-assembly, or “growing” particular nanostructures to be used as sensors. This most often entails one of two types of assembly. The first involves using a piece of some previously created or naturally formed nanostructure and immersing it in free atoms of its own kind. After a given period, the structure, having an irregular surface that would make it prone to attracting more molecules as a continuation of its current pattern, would capture some of the free atoms and continue to form more of itself to make larger components of nano sensors.

                         The purpose of using nano-sensors in this device particularly to identify the bombs before reaching the airport and by using nanogrid is mainly to detect the bombs after it get sensed by the nanosensors.


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