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Nanotechnology Enabled Sensor Applications

Lt Col Sanjiv Tomar is Research Fellow at the Institute for Defence Studies and Analyses, New Delhi. Click here for detailed profile.
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  • July-December 2014
    Invited Articles

    Use or threat of use of the Chemical and Biological Weapons (CBW) remains one of the most dreaded consequences of any modern day conflict. History is strewn with examples of use of chemical and biological agents for tactical or strategic advantage. These weapons whether deployed or used as a threat, act as deterrence against any kind of conventional attack.

    Although banned for their use under the 1972 Biological and Toxin Weapon Convention (BWC) and the 1993 Chemical Weapons Convention (CWC), CBW still pose a great threat to global security due to misuse of existing and emerging new techniques in developing viruses from synthetic materials, making existing diseases more harmful and developing chemicals that can alter consciousness, behavior or fertility.1 With rising extremism in many parts of the world, the possibility of terrorist organizations gaining control of some of the stockpiles of weapons of mass destruction, especially biological and chemical agents, cannot be ruled out.

    Use of chemical weapons in the Syrian conflict demonstrated their destructive capacity. Consequently, early detection of such agents assumes foremost importance. This calls for highly sensitive, accurate and miniature scale sensors that can be deployed in sensitive or border areas for early warning. The use of sensor network is also relevant in detecting any deadly virus as currently being witnessed by a number of countries across the globe after the outbreak of Ebola virus.

    Conventional detectors for chemical warfare agents involve ion mobility spectroscopy, flame photometry, infrared spectroscopy, raman spectroscopy, surface acoustic wave and flame ionization.2 Detection of biological warfare agents is carried out by the use of bioreceptors integrated with an electrochemical, optical, thermal or piezoelectric transducer which on contact with a microorganism, enzyme, antibodies etc. converts the biological signal into a digital signal. Both of these detection methods have disadvantages in terms of selectivity, sensitivity, portability, and power requirements. Their autonomous deployment is practically not feasible due to large size, requirement of continuous power source and real time monitoring.

    Recent advances in the field of nanotechnology have paved the way in designing nanoscale sensors that enable very fast detection and analysis with a rapid response time. Nanotechnology manipulates matter at the atomic, molecular or macromolecular levels to create and control objects at nanometer scale, with the goal of fabricating novel materials, devices and systems that have new properties and functions because of their small size.3 Due to their extremely small size, large surface area, low power requirement and selectivity, nanosensors have a big advantage over conventional detection methods that are often time consuming and have low selectivity and sensitivity. Not only nanosensors can be manufactured purely based on nanomaterials, they can also be integrated with existing chemical or biological sensors to enhance their efficacy.

    Use of nanoparticles and nanocrystals as sensing surface is possible due to their diameters being of the order of biological and chemical species against which they are employed for detection while at the same time requiring a very small amount of sample. These novel nanosensors are capable of detecting and measuring physical characteristics of nanostructures just a few nanometer in size, chemical compounds in concentrations as low as one part per billion or the presence of biological agents such as virus, bacteria or cancerous cells.4

    Development of carbon nanotube (CNT) for the use of nanosensors has given rise to new opportunities in developing CNT based electrochemical nanosensors. Single-wall nanotubes (SWNTs) and multi-wall nanotubes (MWNTs) offer excellent electrical properties resulting in highly agile and power efficient electronics which is highly desirable for nanosensors. At the same time, they also exhibit outstanding mechanical properties thereby making them viable for their outdoor deployment.

    Use of nanowires as sensors utilizing the principle of field effect transistors has given way in achieving specific sensing by linking a recognition group to the surface of the nanowire.5 Development of the stat-of-the-art sensor array with a large number of addressable elements capable of detecting multiple viruses at a level of single distinguishable virus is highly significant. In order to achieve selectivity, CNTs can also be selectively mixed or doped with different materials. With this development, disadvantage of conventional sensors designed to address single or few specific types of virus or chemicalspecies has been overcome. Another attractive application of nanosensors is in the form of sensor arrays in which a large number of addressable elements are fabricated on a single chip that is then able to provide multiplexed detection of diverse biological and chemical entities. Deployment of these kinds of nanosensors arrays can help in detecting biological or chemical agents simultaneously, thus eliminating the use of two different sets of detectors for both types.

    Ongoing research in integrating nanotechnology with other disciplines of science and technology is likely to bring about key changes in military preparedness and national security. Nanosensors will offer the capability of providing early warning of an impending chemical or biological attack resulting in shorter decision cycles thereby protecting human lives, critical infrastructure and resources.