Patterned and switchable surfaces for biomaterial applications

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Chapter 5 – Surface plasmon resonance imaging of polymer microarraysMomentum matching conditions are not satisfied when light illuminates a planarmetal/dielectric interface, requiring the Kretschmann configuration [251] to beadopted whereby attenuated total internal reflectance through a glass prism is used toexcite surface plasmons by the resultant evanescent wave. A typical Kretschmannconfiguration is shown in Figure 5.1A. One face of the Kretschmann glass prism iscoated with a metal. The evanescent light wave produced when light is directed at aspecific angle of incidence through the prism and reflected off the glass/metalinterface excites surface plasmons when the wave vector of the evanescent light (K ev )equals the wave vector of the surface plasmon (K sp ). The excitation of surfaceplasmons is maximised at a specific resonance angle. K ev is given by equation 5.1where w 0 is the frequency of the incident light, c is the speed of light in vacuum, η g isthe refractive index of the glass prism and θ is the angle of incidence of the light[247].w0Kev gsin(5.1)cK sp is given by equation 5.2 where ε m is the dielectric constant of the metal filmand η s is the refractive index of the dielectric [247].Kspw 20 m s (5.2)2c msBy the criterion of equality of equation 5.1 and 5.2, it can be seen that changes inthe refractive index of the dielectric, the angle of incidence or the wavelength of theincident light impacts greatly on the excitation of surface plasmons [247]. SPRexperimental setups endeavour to measure changes in SPR reflectivity withwavelength or angle of incidence.5-160
Andrew Hook – Patterned and switchable surfaces for biomaterial applicationsThe resulting surface plasmons are evanescent waves that have an intensitymaximum at the metal/dielectric interface that decays exponentially into thedielectric to a penetration depth of about 200 nm. Thus, changes in the dielectricproperties within 200 nm of the dielectric material in contact with the metal coatingwill alter the excitation of the surface plasmons, the change of which can be detectedby changes in the intensity of the reflected light [248]. In a typical experiment, lightis coupled into the prism at a fixed angle of incidence, whereupon, for a plot ofreflectivity against angle of incidence the absolute value of the differentialof reflectivity versus angle of incidence is maximised. This is typically at an angleslightly lower than the resonance angle. The intensity of the reflected light ismonitored. The reverse side of the metal coating is then primed with a suitable bufferbefore a molecule of interest is flowed over the metal surface (Figure 5.1A). Thedetection of an adsorption event, as injected molecules of interest replace buffermolecules associated with the surface, can be detected by a sudden increase in thereflected light intensity (Figure 5.1B) as a result of a shift in the resonance angle(Figure 5.1C) associated with a change in the refractive index of the dielectric. Thisincrease will reach a plateau as the surface is saturated with the molecule of interest,and will finally decrease with washing of buffer to remove loosely bound moleculeof interest. Thus, the difference in the initial and final intensity of the reflected lightis a result of the adsorption of the molecules of interest and, when a monochromaticlight source is used, can be related to the shift in the resonance angle required tofulfil K ev = K sp (Figure 5.1C) [247].SPRi, or SPR microscopy, is achieved by coupling SPR with imaging [252, 253].Typically, the reflected light from an SPR experiment is detected by a camera orviewed through a microscope, enabling spatial measurements of changes in the5-161
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Patterned andswitchable surfacesfor
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TABLE OF CONTENTSTABLE OF CONTENTS
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CHAPTER 1.INTRODUCTION1The content
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Chapter 1 - Introductionconsiderabl
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Chapter 1 - Introductioninteraction
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Chapter 1 - IntroductionIn general,
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Chapter 1 - IntroductionFor some ap
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Chapter 1 - Introductionangles rang
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Chapter 1 - Introductionof understa
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Chapter 1 - IntroductionSeveral str
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Chapter 1 - Introductioncues to con
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Chapter 1 - Introductionby controll
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Chapter 1 - Introduction1.2.2. Soft
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Chapter 1 - Introductionsubstrate.
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Chapter 1 - Introduction(A)(B)Figur
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Chapter 1 - Introduction(A)(B)(C)(C
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Chapter 1 - Introductioncomplex gen
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Chapter 1 - Introductionmorphology
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Chapter 1 - Introduction(A)(B)(C)(D
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Chapter 1 - Introductionthe LCST, a
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Chapter 1 - IntroductionHyun et al.
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Chapter 1 - Introductionmicelles. T
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Chapter 1 - Introduction1.4.1. DNA
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Chapter 1 - IntroductionA major pro
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Chapter 1 - Introductionattached to
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Chapter 1 - IntroductionTable 1.1.
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Chapter 1 - Introductionefficiencie
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Chapter 1 - Introductionachieved by
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Chapter 1 - IntroductionTable 1.2.
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Chapter 1 - IntroductionOnce releas
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Chapter 1 - Introductionimaging not
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Chapter 1 - IntroductionA number of
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CHAPTER 2.SPATIALLY CONTROLLED ELEC
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CHAPTER 3.COMPARISON OF THE BINDING
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Patterned and switchable surfaces for biomaterial applications

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