NANOSENSORS *
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4.5 APPLICATIONS .1 MEDICINE
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the porosity of the material controls the wavelength of the emitted light. With a lower material porosity, longer wavelengths will be emitted, and with a higher material porosity, shorter wavelengths will be emitted. For example, materials with about 40% porosity will emit red light, while materials with a porosity of greater than 70% emit a blue/green light (Riu, 2005).
The luminescence porous silicon can also be altered when molecules are incorporated into the porous layer. This unique property has allowed for the design of gas sensors in which the response can be monitored by visually observing a change in colors.
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rapid electrical resistance change within the nanosensor when it is exposed to the VOC. These nanosen- sors are able to detect different types of cancers such as lung, colon, breast, and prostate and allow for early detection, thus ultimately increasing the chance of patient survival (Peng, 2010; Tisch, 2010).
The study of human telomerase in the human body is an interesting topic because of its ability to lead to cell immortality. Human telomerase is a ribonucleoprotein reverse transcriptase, an enzyme that catalyzes the addition of telomeric ends of each chromosome. When this telomeric sequence reaches a critical length, the cell enters cell atrophy and perishes. Human telomerase is extremely hard to detect, and therefore developing a nanosensor that is able to detect its enzymatic activity and presence is a step in the right direction. The study of human telomerase in cancer cells (which contain an abundant amount of telomerase due to their inability to stop replication) will enable scientists to see how cells are ultimately reproduced (Perez, 2008).
In recent years, there has been a shift in focus to develop a nanosensor that is capable of directly measuring glucose levels. This shift has brought about a fluorescent-based nanosensor. These nanosensors offer the benefit of providing continuous monitoring and can be implanted into the skin, an approach that is referred to as the smart tattoo. This allows the tattoo to change its fluorescent properties in response to the blood glucose level of the diabetic patient. If the glucose level falls, the tattoo properties will change and tell the patient that insulin is needed within the blood (Kevin, 2010;
Samuel, 2011).
The use of nanosensors in the medical field for early detection of various diseases through human breath will have a profound effect on medical diagnostics in the future. This will allow doctors to monitor for certain biomarkers allowing them to diagnosis the onset of diseases and cancer in patients.
The ability to do this accurately and quickly will increase the longevity of patient life. The ability to create a smart tattoo that detects glucose levels in blood will vastly increase the comfort of diabetic patients. The smart tattoo will allow for continuous monitoring and allow patients to forgo archaic glucose measurement techniques. The study of human telomerase and how it affects cell reproduction will allow scientists to see how tumors ultimately function, thus increasing the chance of a cure for cancer. All of this is possible with the advent of nanosensors and their ability to heavily influence the medical field.
4.5.2 SECURITY
The ability for nanosensors to detect harmful chemical and biological constituents in the atmosphere is becoming a largely funded field. This area of research is of keen importance to various national defense companies and governments. The ability to detect trace amounts of explosives such as trinitrotoluene (TNT) by the use of nanosensors is a prime example of how the nanosensors can be used for preventa- tive security measures. Nanosensors that are able to detect chemical, biological, nuclear, and radiologi- cal hazards are also currently in development today.
Nanosensors that are capable of detecting trace amounts of various explosives, such as TNT, in the presence of interferents, such as air or other gases, are in the early stages of development. The sensor that is able to detect for TNT currently employs a hybrid detection mechanism that simultane- ously measures the electrochemical current from the reduction of TNT and the change in conductance associated with that reduction. This sensor has useful applications in civilian and military industry. For
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example, it can be used to detect for explosives on boarding passengers or to detect for explosives in a live battlefield (Aguilar, 2010).
Nanosenors are also able to detect biological and chemical containments that can be used as weap- ons. Nanosensors that can detect for these constituents use fluorescent nanoparticles, also known as QDs, which are conjugated to fragmented antibodies of the targeted contaminant. When the wave- length dispersive detectors (WDS) are coupled with a quencher (i.e., an antigen), it allows for sufficient fluorescent resonance energy transfer to quench the QD emissions. A subsequent addition of targeted antigen then displaces the bacteria eliminating the resonance energy and causing an increase in QD photoluminescence. This novelty allows for a large application of broad range detection for bacterial and chemical containments. This will allow for quick and easy methods to be developed that will test for any time that biological or chemical agents have already been used. This early detection is key since the proper countermeasure agent can then be administered to the group of people that have been afflicted with the chemical or biological weapon (Ashok, 2009).
These are two quick examples of how nanosensors can help in the security industry by allowing for detection of explosives and or different types of weapons. This knowledge can be used to accurately and quickly treat any threats or diseases that are present in the vicinity.
4.5.3 ENVIRONMENTAL
Nanosensors also have various applications in the environmental field. The ability to sense for chemi- cals and biological agents that are present in the air and water is a concern to environmental agencies.
Nanosensors will innovate the ways air and water quality is measured due to their size, quickness, and accuracy of measurements. An example of this is detecting mercury in any medium (such as air and water) through the use of dandelion-like Au/polyaniline (PANI) nanoparticles in conjunction with sur- face-enhanced Raman spectroscopy (SERS) nanosensors (Wang et al., 2011).
The ability for nanosensors to measure air quality, particularly for pollutants, is a new approach to air sampling. Nanosensors have already been used to measure solar irradiance, aerosol cloud inter- actions, climate forcing, and other biogeochemical cycles of East Asia and the Pacific region. Such instrumentation has been useful in tracking air pollution in Beijing during the summer Olympic Games (Dybas, 2008). Nanosensors have also been used by an Israeli start-up company that will monitor and analyze emissions from vehicle engines in order to meet the ever increasing strict standards of American and European Environmental agencies (Brinn, 2006).
Nanosensors can also be used in monitoring water distribution and water quality. Due to the loss of water from leaky pipes and mains, the Environmental Protection Agency has designed an innova- tive way to improve the water supply infrastructure via a highly cost-effective monitoring system. This
“Smart Pipe” prototype is built from a multisensor array that will monitor water flow and quality using nanosensors. It will allow for real-time monitoring of flow rates, pipe pressures, stagnant points, slow flow sections, pipe leakage, backflow, and water quality without altering flow conditions in the already- existing infrastructure (Lin, 2009).
These are just some applications of nanosensors that are used in the environmental field. There are numerous others applications in sensing environmental disturbances, but the two most popular ones are: air quality and water quality/quantity measurements.
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4.5.4 INDUSTRIAL
Nanosensors also have useful applications in the industrial field. One of the most prominent applica- tions is the ability to detect various industrial gas leaks. Techniques to detect gas leaks include the use of detecting chemical agents such as differential absorption, light detection, and ranging, along with terahertz frequency-based sensing systems. These two systems are capable of detecting gas at ppm to ppb ranges and are portable and easy to use. The sensor is based on a ridged wave guide with various dielectric materials that are structured periodically in an array. The sensor functions by detecting the concentration of industrial gas changes based on the changes in the effective refractive index of the core in the sensor while the industrial gas fills up the receptor space. This type of sensor is small and portable allowing for easy use and a wide range of applications in detecting industrial gases. The three gases that were tested in this cause were: hydrogen sulfide, carbon dioxide, and sulfur dioxide (Sengupta, 2009).