DETECTING OF BOMBS
USING
NANOTECHNOLOGY
By
Moses dhilip kumar
ABSTRACT:
“ 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")
INTRODUCTION:
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.
PREPARATION:
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.
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 
his 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.
TNT
REPRESENTATION
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
Nanosensor:
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.
CONCLUSION:
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.
