electronics NANO SENSORS TECHNOLOGY M Deepthi M Deepthi N Ambica ¾ by lakshmidhar


									                NANO-SENSORS TECHNOLOGY

M. Deepthi M. Deepthi                               N. Ambica
¾, CSE                                              ¾, CSE
Chaitanya Engineering College                       Chaitanya Engineering College
Mahurawada                                          Mahurawada


      Nanotechnology enables us to create functional materials, devices, and systems by

controlling matter at the atomic and molecular scales, and to exploit novel properties and

phenomena. Nanotechnology enables us to design sensors that are much smaller, less

power hungry, and more sensitive than current micro- or macrosensors. This paper

envisages the technology behind nano sensors . The literary review and the possibilities

of the technology are briefly discussed.The increased integrated technologies in different

stages of nano sensors are elucidated.The advances in the manufacturing techniques of

the nano sensor using MEMS and other devices are detailed.The computational design

involved and the realities behind the technology implementation are highlighted. The

design problems are intensified and the applications of nano sensors in different fields

like physical sensors,electrometers,chemical sensors, bio sensors,deployable sensors are

elucidated.Finally nano-scale materials and devices being integrated into real-world

systems, and the future looks very bright indeed for technology on a tiny scale.
                Nanotechnology enables us to create functional materials, devices, and

systems by controlling matter at the atomic and molecular scales, and to exploit novel

properties and phenomena . Consider that most chemical and biological sensors, as well

as many physical sensors, depend on interactions occurring at these levels and an idea of

the effect nanotechnology will have on the sensor world can be analyzed.

                 Nanosensors and nano-enabled sensors have applications in many

industries, among them transportation, communications, building and facilities, medicine,

safety, and national security, including both homeland defense and military operations.

Consider nanowire sensors that detect chemicals and biologics, nanosensors placed in

blood cells to detect early radiation damage in astronauts, and nanoshells that detect

and destroy tumors. Many start-up companies are already at work developing these

devices in an effort to get in at the beginning. Funding for nanotechnology increased by

more than a factor of 5 between 1997 and 2003, and is still on the rise. So this is a

good time to examine the possibilities—and the limitations—of this small new world

            The particular importance of this technology is the ability to manipulate

individual atoms in a controlled fashion—a sort of atomic bricklaying—by techniques

such as scanning probe microscopy. Initial successes in producing significant amounts of

silver and gold nanoparticles helped to draw even more attention, as did the discovery

that the materials and devices on the atomic and molecular scales have new and useful
properties due in part to surface and quantum effects.

Figure 1. Carbon nanotubes can exist in a variety of forms and can be either metallic or

semiconducting in nature, depending on their atomic structure.

Figure 1. Carbon nanotubes can exist in a variety of forms and can be either metallic or semi conducting in
                              nature, depending on their atomic structure.

              Another major contributor was the creation of carbon nanotubes (CNTs),

extremely narrow, hollow cylinders made of carbon atoms. Both single- and multi-walled

CNTs could, for example, be functionalized at their ends to act as biosensors for DNA or

proteins. The single-walled versions can have different geometries (see Figure 1).

Depending on the exact orientation of the carbon atoms, a CNT can exhibit either

conducting (metallic) or semiconducting properties. This characteristic, and the ability to

grow CNTs at specific locations and manipulated afterward, make it likely that the tubes

will be important for electronics and sensors. For instance, they can be used in the

fabrication of nano field-effect transistors for electronics or as biological probes for

sensors, either singly or as an array.

                      Increasingly Integrated Technologies
                 The technologies associated with materials, devices, and systems were

once relatively separate, but integration has become the ideal. First, transistors were made

into ICs. Next came the integration of micro-optics and micromechanics into devices that
were packaged individually and mounted on PCBs. The use of flip chips (where the chip

is the package), and placement of passive components within PCBs, are blurring the

distinction between devices and systems. The high levels of integration made possible by

nanotechnology has made the material essentially the device and possibly also the

system. Nanotech takes the complexity out of the system and puts it in the material.

              Contemplation of sensing the interaction of a small number of molecules,

processing and transmitting the data with a small number of electrons, and storing the

information in nanometer-scale structures. Fluorescence and other means of single-

molecule detection are being developed. working on data storage

systems that use proximal probes to make and read nanometer-scale indentations in
polymers. These systems promise read/write densities near 1 × 10 bits/sq. in., far in

excess of current magnetic storage capabilities. Although presenting a significant

challenge, integration of nano-scale technologies could lead to tiny, low-power, smart

sensors that could be manufactured cheaply in large numbers. Their service areas could

include in situ sensing of structural materials, sensor redundancy in systems, and size-

and weight-constrained structures such as satellites and space platforms.

             Nanomaterials and nanostructures are other promising application areas.

Two functions often separated in many sensors, especially those for chemicals and

biological substances, are recognition of the molecule or other object of interest and

transduction Ûf that recognition event into a useful signal. Nanotechnology will enable us

to design sensors that are much smaller, less power hungry, and more sensitive than

current micro- or macrosensors. Sensing applications will thus enjoy benefits far beyond
those offered by MEMS and other microsensors.

                           Manufacturing Advances
                   Recent advances in top-down manufacturing processes have spurred

both micro- and nanotechnologies. Makers of leading-edge ICs use lithography, etching,

and deposition to sculpt a substrate such as silicon and build structures on it.

Conven.tional micrýelectronics has approached the nanometer scale—line widths in chips

are near the 100 nm level and are continuing to shrink. MEMS devices are constructed in

a similar top-down process. As these processes begin working on smaller and smaller

dimensions, they can be used to make a variety of nanotechnology components, much as

a large lathe can be used to make small parts in a machine shop.In the nano arena, various

bottom-up methods use individual atoms and molecules to build useful structures. Under

the right conditions, the atoms, molecules, and larger units can self-assemble

Alternatively, directed assembly can be used. In either case, the combination of nano-

scale top-down and bottom-up processes gives materials and device designers a wide

variety of old and new tools

                               Computational Design
        Recently developed experimental tools, notably synchrotron X-radiation and

nuclear magnetic resonance, have revealed the atomic structures of many complex

molecules. But this knowledge is not enough; we need to understand the interactions of

atoms and molecules in the recognition and sometimes the transduction stages of sensing.

The availability of powerful computers and algorithms for simulating nano-scale

interactions means that we can design nanosensors computationally, and not just
experimentally, by using the molecular dynamics codes and calculations that are already

fundamental tools in nanotechnology.

                Although the excitement over nanotechnology and its prospective uses is

generally well founded, the development and integration of nanosensors must take into

account the realities imposed by physics, chemistry, biology, engineering, and commerce.

For example, as nanotechnologies are integrated into macro-sized systems, we’ll have to

provide for and control the flow of matter, energy, and information between the nano and

macro scales.

                          Design Problems Intensified
                Many of the design considerations for nanosensors are similar to those for

microsensors, notably interface requirements, heat dissipation, and the need to deal with

interference and noise, both electrical and mechanical. Each interface in a microsystem is

subject to unwanted transmission of electrical, mechanical, thermal, and, possibly,

chemical, acoustical, and optical fluxes. Dealing with unwanted molecules and signals in

very small systems often requires ancillary equipment and low-temperature operation to

reduce noise. Flow control is especially critical in chemical and biological sensors into

which gaseous or liquid analytes are brought and from which they are expelled.

Furthermore, the very sensitive, tailored surfaces of these sensors are prone to

degradation from the effects of foreign substances, heat, and cold. But the ability to

install hundreds of sensors in a small space allows malfunctioning devices to be ignored

in favor of good ones, thus prolonging a system’s useful lifetime.
                                    Risk and Economics
              The path from research to engineering to products to revenues to profits to

sustained commercial operations, difficult for technologies of any scale, is particularly

challenging for nanotechnologies. One major impediment to their adoption is the

common reluctance to specify new technologies for high-value systems. Another is that

at present most nano-scale materials are hard to produce in large volumes, so unit prices

are high and markets are limited. Costs will decrease over time, but small companies may

have a struggle making their profit goals quickly enough to survive

        Few sensors today are based on pure nanoscience, and the development of nano-

enabled sensors is in the early stages; yet we can already Foresee some of the possible

devices and applications. Sensors for physical properties were the focus of some early

development efforts, but nanotechnology will contribute most heavily to realizing the

potential of chemical and biosensors for safety, medical, and other purposes. Vo-Dinh,

Cullum, and Stokes recently provided an overview of nanosensors and biochips for the

detection of biomolecules

Figure 2. The mass of a carbon sphere shifts the resonance frequency of the carbon nanotube to which it is

Physical Sensors. The world’s smallest “balance” (see Figure 2) by taking advantage of
the unique electrical and mechanical properties of carbon nanotubes. They mounted a

single particle on the end of a CNT and applied an electrical charge to it, Acting much

like a strong flexible spring, the CNT oscillated, without breaking, and the mass of the

particle was calculated from changes in the resonance vibrational frequency with and

without the particle. This approach may allow the mass of individual biomolecules to be


   Figure 3. A nanometer-scale mechanical electrometer consists of a torsional mechanical resonator, a
detection electrode, and a gate electrode used to couple charge to the mechanical element. A schematic and
                   micrographs of a single element and an array of elements are shown

Electrometers. Fabrication and characterization of a working, submicron mechanical

electrometer is devised. This device (see Figure 3) has demonstrated charge sensitivity

below a single electron charge per unit bandwidth (~0.1 electrons/ Hz at 2.61 MHz),

better than that of state-of-the-art semiconductor devices.

Chemical Sensors. Various nanotube-based gas sensors have been described in the past

few years. a miniaturized gas ionization detector based on CNTs The sensor could be

used for gas chromatography. is developed
 Figure 4. This nano-array incorporates capacitive readout cantilevers and electronics for signal analysis.

             Titania nanotube hydrogen sensors have been incorporated in a wireless

sensor network to detect hydrogen concentrations in the atmosphere. And Kong et al.

have developed a chemical sensor for gaseous molecules such as NO2 and NH3 that is

based on nanotube molecular wires

             A focused ion beam technique to fabricate nanocantilevers (see Figure 4) and

have developed an electron transfer transduction approach to measure cantilever motion .

The results might be sensitive enough to detect single chemical and biological molecules.

Structurally modified semiconducting nanobelts of ZnO has also been demonstrated

applicable to nanocantilever sensors.

Figure 5. DNA and other biomaterials can be sensed using encoded antibodies on Nanobarcodes particles.

Biosensors. Nanotechnology will also enable the very selective, sensitive detection of a

broad range of biomolecules. By using the sequential electrochemical reduction of the

metal ions onto an alumina template, we can now create cylindrical rods made up of

metal sections 50 nm to 5 microns long. These particles, trademarked Nanobarcodes (see
Figure 5), can be coated with analyte-specific entities such as antibodies for selective

detection of complex molecules. DNA detection with these nano-scale coded particles

has also been demonstrated. The surface of a chip is covered with millions of vertically

mounted CNTs 30–50 nm in dia. (see Figure 6). When the DNA molecules attached to

the ends of the nanotubes are placed in a liquid containing DNA molecules of interest, the

DNA on the chip attaches to the target and increases its electrical conductivity. This

technique, expected to reach the sensitivity of fluorescence-based detection systems may

find the application in the development of a portable sensor.

Figure 6. Vertical carbon nanotubes are grown on a silicon chip. DNA molecules attached at the ends of the
                            tubes detect specific types of DNA in an analyte.

Deployable Nanosensors. The SnifferSTAR, a lightweight, portable chemical detection

system (see Figure 7), is a good example of nanotechnology’s potential for field

applications This unique system combines a nanomaterial for sample collection and

concentration with a MEMÄ-based chemical lab-on-a-chip detector. SnifferSTAR will

likely find work in defense and homeland security and is ideal for deployment on

unmanned systems such as micro unmanned aerial vehicles.
  The SnifferSTAR is a nano-enabled chemical sensor integrated into a micro unmanned aerial vehicle

And More. Other areas we expect to benefit from nanotechnology-based sensors include

transportation (land, sea, air, and space); communications (wired and wireless, optical,

and RF); buildings and facilities (homes, offices, factories); humans (especially for health

and medical monitoring); and robotics of all types

Nanotechnology is certain to improve existing sensors and be a strong force in

developing new ones. The field is progressing, but considerable work must be done

before we see its full impact. Among the obvious challenges are reducing the cost of

materials and devices, improving reliability, and packaging the devices into useful

products. Nevertheless, we are beginning to see nano-scale materials and devices being

integrated into real-world systems, and the future looks very bright indeed for technology

on a tiny scale.

1.Small Wonders, Endless Frontiers: A Review of the National Nanotechnology
Initiative, National Academy Press, 2002.

2. Cui, Y., et al., Nanowire Nanosensors for Highly Sensitive and Selective Detection of
Biological and Chemical Species, Science , Vol. 293, Aug. 17, 2001, pp. 1289-1292.

3. Space Mission for Nanosensors, The Futurist , Nov./Dec. 2002, p. 13.

4. Cassell, J.A., DoD grants $3M to Study Nanoshells for Early Detection, Treatment of
Breast Cancer, NanoBiotech News , Vol. 1, No. 3, Aug. 13, 2003.

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