Final Project on Nanotechnology and Nanosensors Course George Georgiadis
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Table of Contents
Abstract .................................................................................................................................................... 3 Introduction .............................................................................................................................................. 3 Literature Review ..................................................................................................................................... 3 Project Description ................................................................................................................................... 4 Conclusions and Recommendations ........................................................................................................ 7 References ................................................................................................................................................ 8
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Abstract The goal of nanotechnology is to allow for an enormous array of human enhancements and medical treatments. In the long run, nanotechnology will enable us to analyze and repair any physical ailment in the body. This means that nanotechnology will be able to repair someone who is damaged or diseased back to full health. The ultimate result could be the end of pain, disease, and aging. The aim of this project is to propose a fully functional system based on optical nanosensors which would contribute to making the daily life of the visually impaired considerably easier.
Introduction Blindness is one of the worst human ailments. Although crossing busy roads can be a challenge for people with good vision, for blind people or visually impaired could be a fatal choice. The proposed electronic eye aims at helping millions of blind and visually impaired people obtain more independent lives. The electronic eye can be adapted to help the blind or visually impaired get around without a walking stick or seeing-eye dog. GPS can tell what streets, restaurants, parks and other landmarks the user is passing. Devices like these are very good at giving locations and directions. But the limitation of GPS technology is that they cannot pin down the location of a curb or crosswalk and frequently fail in areas that have many tall buildings and high traffic. Thus, the proposed system with an optical nanosensor substituting their vision in conjunction with image capture system and a voice speech system giving vocal messages and information through a small speaker near the ear is expected to improve their daily life.
Literature Review In the following books, “Nanosensors for Chemical and Biological Applications” [4] and “Nanomedical Device and Systems Design Challenges” [5], nanosensors and their application to medicine are thoroughly described. Extensive information about their fabrication and characterization is also provided. In the “Nanotechnology and Nanosensors, Introduction to Nanotechnology” [3] e-book, carbon-based nanotubes (CNTs) are discussed and interesting knowledge about their structure, properties and synthesis methods can be obtained. In the papers “Triboelectric Nanogenerator as an Active UV Photodetector” [1] and “Graphene photodetectors with ultra-broadband and high responsivity at room temperature” [2] one can learn about innovative methods of fabricating and applying nanosensors being able to detect light over a broad sprectal range.
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Project Description Many optical biosensors that are based on the phenomenon of surface plasmon resonance may be considered as evanescent wave techniques. They utilize a property that is inherent to gold and other materials, specifically that a thin layer of gold on a high refractive index glass surface may absorb laser light to produce electron waves (surface plasmons) on the surface of the gold. This occurs only at a specific angle and wavelength of incident light, and is highly dependent on the surface attributes of the gold, such that the binding of a target analyte to a receptor on the gold surface produces a measurable signal. Surface plasmon resonance sensors operate using a sensor chip that consists of a plastic cassette that supports a glass plate, one side of which is coated with a microscopically thin layer of gold. This is the surface that contacts the optical detection apparatus of the instrument. The opposite side is then interfaced with a microfluidic flow system. Contact with the flow system creates channels across which reagents may be passed in solution. This side of the glass sensor chip may be modified in a number of ways to allow for the easy attachment of molecules of interest (FIGURE 2). Light of a fixed wavelength is reflected from the gold side of the chip at the angle of total internal reflection and is detected inside the instrument. This induces the evanescent wave to penetrate through the glass plate and some distance into the liquid that is flowing over the surface. The refractive index at the flow region of the chip surface has a direct influence on the behavior of the light that is reflected from the gold region. Binding to the flow region of the chip has an effect on the refractive index, and in this way biological interactions may be measured with a high degree of sensitivity when facilitated by a source of energy. However, there are also disadvantages of surface plasmon resonance, as it cannot easily discriminate between specific and non-specific interactions with the sensor surface. Elaborate washing does not completely remove the non-specifically bound material; thus, reference material or control samples are needed to correct for the non-specific binding. Because SPR is mass sensitive, the sensitivity for high molecular weight molecules is good, but binding of low molecular weight compounds is more difficult to detect. In addition, a particular challenge in SPR application is the limited sensor area, leading to a diminished capacity.
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In addition, rising interest in the possible use of optical sensors for miniaturized devices has lead to an extensive study of chalcogenide glasses (ChGl) in recent years due to their flexible structure, enormous variation in properties, and almost unlimited ability of doping and alloying making them promising materials for sensors for monitoring pollutant gases in the environment. Moreover, ChGls are conducive for use in fiber optics and integrated optics since they have many unique optical properties . Due to their 5
IR transparency, photosensitivity, high optical nonlinearity, and rare-earth doping potential, these glasses have been utilized to fabricate photonic devices such as fibers, planar waveguides, gratings, all-optical switches fiber amplifiers. Germanium chalcogenides have traditionally been used for mid-IR fibers with transmission windows up to 12 mm. Germanium-doped chalcogenides exhibit photoconductivity and band gap shrinkage with increasing doping, suggesting their potential application in low-cost mid-IR detection, which necessitates the investigation of their optical properties and their ability to appropriately modify the band structure. For many of above mentioned applications, thin films are necessary. The wide practical application of thin amorphous chalcogenide films, especially of vitreous Ge-containing condensates, is closely connected with their transparency in the visible and near IR spectral regions and with the possibility to create optical media with defined values of the refractive index, dispersion, and extinction coefficient. The relatively low energy of the chemical bonds in Ge-based chalcogenide glasses offers the opportunity for photostructural transformations and a number of other light-induced effects, all of which are typically accompanied by considerable changes in the optical constants of thechalcogenides. Many methods for thin film preparation have been studied. Some include spin-coating, evaporation of one or more materials at low pressures and high temperature in vacuum, ionic and magnetron sputtering, pulsed laser deposition, and chemical vapor deposition. The preparation of chalcogenide thin films of complex compositions can be a difficult task and classical deposition methods can often not be used to form films with a strict stoichiometry match to the target. Concerning the fabrication of the proposed nanosensor the following steps are taken: 1. Bulk Glass Synthesis: Glassy alloys of (GeSe5)1- xInx (x ¼ 0, 5, 10, 15, 20) are prepared by the quenching technique. The respective amounts of Ge, Se and In elements with 5 N purity are mixed and sealed in quartz ampoules evacuated down to 1.33 x 10-3 Pa. The ampoules are heated with a rate of 2 K/min up to 1,200 K. During heating they are constantly rocked to obtain homogeneous glassy alloys. After holding and rocking for about 12 h, the melt is rapidly quenched in ice-cooled water. 2. Thin Film Deposition: Thin films are deposited from the relevant bulk glasses by thermal vacuum evaporation in a Leybold LB 370 vacuum system. The process conditions are: a residual pressure in the chamber of 1.33 x 10-3 Pa, a distance between the evaporation source and the substrates of 0.12 m, an evaporation area of 1.2 x 10-6 m2 of an inductively heated tantalum evaporator, they are carefully monitored and examined. The substrates are rotated during the deposition to prevent the preparation of inhomogeneous and non-uniform films. The evaporation temperature ranges from 600 to 800 K and it is controlled by a Ni-Ni/Cr thermocouple. The films are annealed in vacuum for 1 h in a furnace at a temperature of 390 below the glass transition temperature of the glasses.
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The output of the chalcogenide thin films ,when they are subjected to light, is increased electrical current. The output is connected to the input of a BJT amplifier, which activates the camera of a Digital Microscopy Image Analyser [6]. The Digital Microscopy Image Analyzer compares the captured images to pattern images stored in a micro SD card and recognizes real objects of the environment. Subsequently, the recognized object is converted to audio signal by a voice speech system and the voice message is transmitted to the receiver (ear) through a speaker. This process iterates at a sensible rate so as the vocal messages to be perceived. For this purpose the Digital Microscopy Image Analyser is configured properly. The proposed nanosensor ensures high sensitivity and uninterrupted function. The diagram of figure 4 describes the overall system structure.
Fig. 4
Conclusions and Recommendations The development of the mobility aids for the visually impaired is a challenging task that has many potential solutions. In this project a sophisticated mechanism is proposed to enhance the mobility of the blind. The proposed system can improve the life of the visually impaired to a great extent and is definitely a better choice compared to traditional solutions. Since cost plays a significant role even in medical treatments, detailed cost analysis has to be conducted. The volume of the system is expected to be practical. On the other hand, the different parts of the system
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pose failure risk and in such case restoration could be difficult. Thus, a compact device which incorporates the proposed system is recommended.
References [1] Advanced Functional Materials, Triboelectric Nanogenerator as an Active UV Photodetector, ZongHong Lin , Gang Cheng , Ya Yang , Yu Sheng Zhou , Sangmin Lee , and Zhong Lin Wang, 2014 [2] Nature Nanotechnology, Graphene photodetectors with ultra-broadband and high responsivity at room temperature Chang-Hua Liu, You-Chia Chang ,TheodoreB.Norris and Zhaohui Zhong, 2014 [3] Nanotechnology and Nanosensors, Introduction to Nanotechnology, Technion Israel Institute of Techology, Prof Hossam Haick [4] Nanosensors for Chemical and Biological Applications, Sensing with Nanotubes, Nanowires and Nanoparticles, Kevin C. Honeychurch
[5] Nanomedical Device and Systems Design Challenges, Possibilities, Visions, Frank J. Boehm [6] http://microvisual.com.my
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