Development of Surface Plasmon Resonance (SPR) Sensor

Development of Surface Plasmon Resonance (SPR) Sensor INTRODUCTION CHAPTER-1 INTRODUCTION The physical processes involved in surface plasmon resonance (SPR) phenomena were first reported by R.M. Wood in 1902 [1]. In this work, Wood observed a repeated pattern of dark and bright light bands in the reflected light, when he irradiated polarized light on a mirror with a diffraction grating on its surface. The physical interpretation of SPR mechanism was first initiated by the British physicist Lord Rayleigh [2], and further refined by Fano [3], but its satisfactory explanation was not available until 1968, when Otto [4] and in the same year Kretschmann and Raether [5] reported the excitation of surface plasmons on the metal/dielectric interface. Its first use in a real-time analysis of a biological system was demonstrated in 1990s by Karlsson et al. [6]. Since then, The SPR has become a crucial optical sensing technique in the areas of biology, microbiology, biochemistry, and medical sciences because of its noninvasive nature [7]. The commercially available SPR based devices are not so cost-effective and require consumable sensor chips demanding certain specifications of size, thickness, effective sensing area and so on. For example, The Biacore (acquired by General Electric Healthcare in 2006), a life science products company, are providing a variety of models of SPR-based instruments (a typical cost of $120,000–$250,000) that exhibit compatibility only with expensive Biacore accessories. Moreover, the associated high operational cost inhibits introduction of SPR technique into laboratory classes at the undergraduate or postgraduate level. In addition to that, the commercial SPR instrument is not a good teaching tool because all the components, of the apparatus, are enclosed, thus preventing the students from visualizing the details of the SPR instrumentation. The primary motivation behind the present project work is to develop a low-cost SPR based multipurpose optical sensor especially intended for undergraduate and postgraduate education and Research. The proposed homemade SPR sensor is supposed to be cost-effective, and whose all components would be accessible for visualization and manipulations in future. The presented design not only allows its integration with various other mechanical and electronic add-ons, but also could prove to be an ingenious teaching tool for the students to understand and appreciate the modern instrumentation. In addition, once developed, this instrument could also serve the Research purposes of general chemistry, biochemistry, physical chemistry, Nanotechnology and Material Sciences. For this purpose it was necessary to arrange low cost experimental components but keeping in mind that these components work well to satisfy our purpose. It took a long time first to decide the components, and then taking overviews from various places regarding the type of component available and the price of that particular component. After comparing and analyzing the need and price of whole set-up the components were arranged from different market places. After arranging the components it was necessary to prepare the experimental set-up in a well mannered way to fulfill our purposes. Again it took a long time to arrange them in a dark room (as we were working on light and its intensity measurement) as to get a well observable result. The most difficult and time consuming task was to produce a thin metallic film on the glass slide of a specific thickness to get a better result. Metallic film was of gold and the coating unit was a magnetron sputtering gold coater available in the department of the institute. Initially it was a difficult task to coat the glass slide of specific thickness, for which we coated various glass slides with different thicknesses using variable coating time of the coater. Then we did the experiments with that thickness but didn’t get the results. Then glass slides were again coated to increase the gold film thickness. This process was repeated various times and at last we were succeeded to produce the res ults from the glass slides of different thicknesses. In this dissertation work, we first introduce the principle of Surface Plasmon Resonance and other associated phenomena. Following the introduction part, we describe some literature reviews in next section of report. We further describe the details of the crucial components that would be used in the development of SPR based Sensor or can be termed as the Experimental Set-up for the Surface Plasmon Resonance phenomenon. The very next section contains the soul of the whole report or the Results, mentioned as results and discussion. We finally conclude the report by enumerating the work done so far, the future course of work followed by the References that have been used for the literature survey. SURFACE PLASMON RESONANCE- Principle: SURFACE PLASMON RESONANCE(SPR): The resonant oscillation of conduction electrons, at the interface between a metal and dielectric, stimulated at the optical frequencies is called the SURFACE PLASMON RESONANCE (SPR). This  resonance  condition is satisfied once the incident  photon frequency matches with the natural frequency of surface electrons, which are oscillating under the action of restoring force of positive nuclei of the metallic atoms. The resonance phenomena has been shown to have many applications such as in Gas detection and immune-sensing [8,9], efficiency enhancement of Solar Cells [10], and Magneto-Optical based imaging etc. [11,12]. Figure 1 shows a typical surface Plasmon resonance set-up which consists of a light source, prism, gold film, and a detector. Figure 1: Schematic diagram of a surface Plasmon resonance set-up. Here n1 and n2 show the refractive indexes of prism and air respectively. SURFACE PLASMON POLARITONS (SPP) wave -The surface  electromagnetic waves, propagating along the  metal/dielectric  or metal/vacuum interface, is known as SURFACE PLASMON POLARITONS (SPP) wave. As the SPP wave is propagating along the boundary of the metal and the external medium (air or dielectric), the aforesaid resonant oscillations become extremely sensitive to any change occurring at the boundary, for instance the adsorption of molecules to the metal surface or change in refractive index at the metal-dielectric surface. Thus the sensitivity associated with metal – dielectric interface can be exploited to obtain a non-destructive and cost effective multipurpose sensor for detection of Chemical and Biological species. According to different literature [9,12], the sensing properties has been quite useful for monitoring food quality, safety analysis, medical diagnostics and environmental changes etc. A typical SPR sensor consists of a dispersive element, such as prism or a plane reflection grating, coated with a metallic layer (Gold) and a dielectric layer (usually polymers or bio molecule layers). The Kretschmann configuration, as shown in Figure 2, is often used in most of the SPR sensor applications, where a metal (typically silver or gold) film is placed at the interface of two dielectric media. The medium 1 with higher refractive index (n1) is a prism and the medium 2 with lower refractive index (n2) can be the air or the dielectric of interest. A collimated p-polarized light beam, entering from the glass side undergoes a total internal reflection and interacts with the metallic layer at the critical angel of incidence (as shown in Figure 2). The surface plasmons (SP), at the metallic surface, are excited at the resonance optical frequency resulting in absorption of a part of incident light energy and hence leading to a sudden drop in Reflectance at a specific angle à ¯Ã‚   ±0 adjacent to the critical angle à ¯Ã‚ Ã‚ ±C. The resonance condition of the SPs is sensitive to any change in the refractive index of the metal-dielectric interface and leads to shift of à ¯Ã‚ Ã‚ ±0 to a new angle à ¯Ã‚ Ã‚ ±1 (Figure 2). The change in the intensity of reflected or diffracted light or its wavelength or angular spectrum can be monitored using a charge coupled device arrays or photodiode arrays, for different sensing purposes [13-16]. Figure 2: Diagram representing the Surface Plasmon Resonance mechanism. TOTAL INTERNAL REFLECTION AND EVANESCENT WAVES: When the light travels from the higher refractive index medium 1 (glass) to the lower refractive index medium 2 (air or dielectric), the total internal reflection (TIR) takes place within medium 1 for the incident angles ÃŽ ¸ greater than the critical angle ÃŽ ¸C, satisfying the Snell’s relation Sin (ÃŽ ¸C) = n2/n1. The Evanescent waves, a near-field wave, are produced in the lower refractive index medium 2 (air or dielectric) under the TIR condition. As the meaning of Evanescent is tending to vanish, the amplitude of evanescent waves decays exponentially with the distance from the point of incidence, to the interface of the media 1 and 2. When a nonmagnetic gold film with a suitable thickness is sandwiched between the media 1 and 2, the amplitude of evanescent wave is enhanced, penetrating in the gold film and also existing simultaneously in the medium 2. Using the well known Fresnel’s relations, magnitude of the parallel wave vector of the evanescent wave, , is expres sed as; (1) where ÃŽ » is the wavelength of the incident light, n1 is the refractive index of the higher refractive index medium 1, and ÃŽ ¸ is the angle of incidence. Figure 3: Schematic diagram showing a layer system of surface Plasmon resonance where kevan and ksp are wave vectors given in equations. SURFACE PLASMONS: Surface plasmons (quanta of plasma), are the surface electromagnetic wave travelling along the limited region of metal–dielectric interface. The magnitude of the wave vector of the surface plasmon is connected to the dielectric constants of medium 2 (n2) and the gold film (ng). For most of the non absorbing materials, the magnetic permeability is very close to unity at optical frequencies. Hence, the dielectric constant for such materials becomes equal to the square of the refractive index i.e. ÃŽ µ = n2. Here ÃŽ µ is the dielectric constant and n is the refractive index. As a result, can be obtained from n2 and ng using the following relation; (2) where n2 is the refractive index of medium 2 adjacent to the interface and ng is the refractive index of the gold film. SURFACE PLASMON RESONANCE: In presence of the evanescent wave, the surface plasmon can be excited leading to the phenomenon of surface plasmon resonance (SPR). In this situation, the intensity of the reflected light, from the metal-dielectric interface, decreases abruptly (as shown in Figure 1). In this process the energy of evanescent wave is conserved and the energy of the excited surface plasmon is coupled to phonons or photons generation at the interface. Hence, the energy conservation requires that equals to . Thus, using eqs 1 and 2 the angle , at which SPR occurs, can be determined by below relation, (3) Here, the incident angle at which the minimum reflectivity is observed is called the SPR angle. The angle has been found to be slightly larger than the critical angle . It is clear from above expression that the angle is linked to n2 if n1 and ng are kept fixed. Hence, even a slight change in the refractive index of interfacial region is reflected in a significant change in the angle . For instance, the phenomena of adsorption and desorption of any gas, on the gold surface, changes the refractive index of media 2 near the metal–dielectric interface leading to change in the . Therefore, the monitoring the change in the angle can be used, as a technique, to study and analyze the adsorption– desorption or association–dissociation phenomena taking place on the gold surface. The refractive index, in the interfacial regime, changes with the mass and density of foreign species attached to the gold film surface. As a consequence, monitoring the change in the SPR angl e provides information about mass and density change on the gold surface, effectively within 200 nm from a metal surface. As mentioned above the surface Plasmon resonance will occur when, Also from the above discussion we know that the is a function of three parameters. The wavelength of incident light. The refractive index of medium 1 or glass prism. Angle of incidence of the incident light falling on the metal-dielectric junction. And also is a function of three parameters, The wavelength of incident light. The refractive index of metallic thin film. The refractive index of the second medium or the air. So we get five different parameters which can be used as varying parameters to get the optimum condition of Surface Plasmon Resonance which are, The wavelength of incident light, The refractive index of medium 1, The refractive index of medium 2, The refractive index of metallic film, and The angle of incidence of incident light. In wavelength interrogation Surface Plasmon Resonance device, wavelength of incident light is varied whereas the other parameters including incident angle, refractive indexes of medium 1, medium 2 and medium 3 are kept constant during the whole experiment. In this case there is a variation in the intensity of reflected light with variation in wavelength of incident light as shown in figure 4. Figure 4: Shows relationship between absorbance of reflected light and the wavelength of incident light. In angle interrogation Surface Plasmon Resonance device, incident angle of light is varied whereas the other parameters including wavelength of incident light, refractive indexes of medium 1, medium 2 and medium 3 are kept constant during the whole experiment. In this case there is a variation in the intensity of reflected light with variation in angle of incident light as shown in figure 5. Figure 5: Diagram indicating the relationship between intensity of reflected light and incident angle. The other type of interrogation device is refractive index interrogation Surface Plasmon Resonance device in which refractive index of any medium is varied which is a tough task and that is why used in very rare cases. Other parameters are kept constant in this type of interrogation system including wavelength of incident light as well as the incident angle of the light. In this case there is a variation in the intensity of reflected light with variation in refractive index of the medium taken in consideration as shown in figure 6. The one other and most complicated interrogation system is phase interrogation Surface Plasmon resonance device in which phase of the reflected light provides the information about the metal dielectric interface. Very less work has been done in this field and is a good topic to work on in future as angle dependent reflectance measurement and other methods discussed above are limited for detecting low weight molecules on the metal dielectric surface. Figure 6: shows relationship between intensity of reflected light and refractive index of the medium with three different gold film thicknesses. Now refractive indexes of medium 1(glass), medium 2(air) and the gold metallic thin film cannot be varied simply during a running experiment. So we have only two parameters which can be used as variable parameters, the wavelength of the incident light and the angle of incidence of that light falling on the set-up. In our work, we have used the later one for our purpose which is angle of incidence of the incident light on the metal dielectric interface, and making the wavelength of the incident light constant near about 650 nm which means we have used a red laser as a source of the light for our experimental set-up. Angle of incidence can be varied either be rotating the light source around the prism or by rotating the prism on its axis and making light source stationary. We are rotating the prism which is mounted on a rotational prism table to vary angle of incidence.

BELIEVE IT OR NOT :: essays research papers

It has always been a myth that sun signs describe who you are. Most of the times, it seems unbelievable to accept the fact that the position of the sun and the planets determine the person’s character, yet we mostly identify firmly with our signs. The characters from Jane Austen’s famous novel, Emma, can be identified with their signs because of their unique personality traits. I believe the protagonist of the novel, Emma Woodhouse, is definitely a Leo. It is stated that â€Å"In grandeur of manner, splendor of bearing and magnanimity of personality, Leos are the monarch’s among humans†. This definition is clearly true for Emma for she bears the nobility in her manners and position. She has a great deal of self confidence, but she also has a great fear of being ridiculed and made to feel disgraced. Though we do not see anyone making fun of her in the novel, she is very much affected by Mr. Knightley upbraiding after she behaves impolitely towards Miss Bates. A Leo is warmhearted, generous, creative, enthusiastic, faithful, ambitious, courageous, dominant, strong willed, independent, self-confident and readily noticed whenever she enters a room. Leos think and act bigger than others would normally dare; â€Å"the ambitiousness of their schemes and idealism sometimes daunt their supporters.† Emma definitely thinks â€Å"bigger† than she should, and her imagination is much beyond the realities. She tries to matchmake Harriet with Mr. Elton, then with Frank Churchill, both who do not have any attachments towards her. â€Å"Leos’ faults can be as large in scale as their virtues, and an excessively negative Leonian can be one of the most unpleasant human beings imaginable, displaying extreme arrogance, snobbish superiority, autocratic pride, haughtiness, and excessive hastiness of temper.† At the scene with the picnic in Donwell’s Abbey, Emma puts Miss Bates down harshly when she begins to chatter continually. Emma’s sharp remark shows her cruelty, arrogance, selfishness, pomposity with the most unpleasant manner. Mostly Leos use their powers for doing good, for they are strongly idealistic, humane, and beneficent, yet they do not hesitate to use cunning, lies and trickery to discredit their rivals if they’re jealous. This becomes true for Emma about her feelings towards Jane Fairfax. She has been brought up like a princess, getting the most attention and love. However, when Miss Bates mentions Jane Fairfax’s letter or Mr. Knightley talks about Jane Fairfax’s beauty and gentleness, Emma suddenly becomes jealous of her.

Critical analysis of “The Lottery” by Shirley Jackson Essay

Overall Shirley Jackson discusses the movement of the setting, the unusual foreshadowing, and the outermost symbolism in â€Å"The Lottery† to give an overall point of view of the story. Even though a small village made seem peaceful, and a good place to raise a family, it is not always what it seems to be. The reader is about to enter a world with ritualistic ceremony and religious orthodoxy in â€Å"The Lottery.† The Lottery takes place on a clear and sunny summer morning around June 27 in a small village with about three hundred villagers gathering together in the central square for the annual lottery. As a child Shirley Jackson was interested in writing; she won a poetry prize at age twelve, and in high school she keeps a diary to record her writing progress. In 1937 she entered Syracuse University, where she published stories in the student literary magazine. Despite her busy life as a wife and a mother of four children, she wrote every day on a disciplined schedule. â€Å"The Lottery† is one of Jackson’s best-known works. In â€Å"The Lottery† Shirley Jackson will discusses the movement of the setting, unusual foreshadowing and outermost symbolism to give us an overall point of view from the story. When one thinks of a lottery, one imagines winning a large sum of money. Shirley Jackson uses the setting in â€Å"The Lottery† to foreshadow an ironic ending. The peaceful and tranquil town described in this story has an annual lottery every June 27 early part of 1800’s in a small village with 300 people (456). Setting is to describe time and place of the story. The story occurs â€Å"around ten o’clock† (456). This is an unusual time because in most towns all the adults would be working during mid-morning. In the lottery an ironic ending is also foretold by the town’s setting being described as one of normalcy. The town square is described as being â€Å"between the post office and the bank† (456). Every normal town has these buildings, which are essential for day-to-day functioning. Throughout the story little parts of setting are being told, to give a clearer picture for a better understanding of the story. Jackson foreshadows a surprise ending. Foreshadowing is to hint of something  that would follow with the story. As the story continues the reader is told that school has let out for the summer, and yet the â€Å"feeling of liberty sits uneasily with the children† (456), which is strange, for no normal kid would be anything less than ecstatic over summer break. Finally, the children are said to be building â€Å"a pile of stones in one corner of the square† (456), which is a very strange game for children to play. All of these hints indicate that something strange and unexpected is going to happen, and they all will make sense once we discuss the story’s final outcome. Symbolism is also a strong element of the story. The introduction of the black box carried by Mr. Summer (456) is a key turning point showing symbolism, which is anything in a story that represents something else, giving the awful ominous answers to all those foreshadowing hints. When the black box is brought in, it’s said to be a tradition that no one liked to upset. The villagers kept their distance from the box, as though they feared it (461). More and more the town’s peculiarity begins to become apparent. For an example, the names of certain residents hit at the irony and unfavorable events to come. From the author’s extravagant detailing of the town, one would expect this â€Å"lottery† to be a chance for one lucky family to win some money. Instead, the winner’s â€Å"prize† is death-by stoning In the story Tessie won the prize when Bill, her husband, forced the paper out of her hand (461). The portrayal of the residents at the end of th e story is disturbing–they go about killing the â€Å"winner† ritualistically, trying to â€Å"finish quickly.† (461). They show no empathy at all–they’re simply following an ancient ritual. Overall Shirley Jackson discusses the movement of the setting, the unusual foreshadowing, and the outermost symbolism in â€Å"The Lottery.† The lesson in this story hits pretty hard. The Lottery’s relationship to real life is that sometimes we are presented with traditions that have been adhered to for as long as anyone can remember, and we forget the reason these customs were created in the first place. The problem is that circumstances can change and make these traditions outdated, useless, and even harmful. Overall the main point of the story is that ignorant and indulgent believers can bring death to an innocent person, so therefore we must re-evaluate our traditions;  otherwise we’re just letting ourselves be stoned.

Lab Safety Sign Quiz (Hazard Symbols)