Surface Plasmon Resonance and Optical Metal Nanoshells

1. Surface Plasmon Resonance and Optical Metal Nanoshells Y. Tzeng Auburn University Auburn, Alabama USA (Second half, nanoshells, was presented by Suiquiong Li for ELEC 7970 instructed by Y. Tzeng, 2003)

2. Outline • What is light? • Electromagnetic wave • Plasmon resonance • Metallic Nanoshells • Optical properties of nanoshells • Fabrication of metallic nanoshells • Applications

3. What is light? Light As A Wave • In the 18th and 19th century, most scientists believed light behaves like a wave • Basic definition of a wave – the displacement of energy propagating along a medium • Some examples of waves – water waves – sound waves – light waves (also called electromagnetic waves) • can propagate in vacuum http://www.howstuffworks.com/light2.htm http://www.astro.utoronto.ca/~swlee/ast201spring/ast201_light_telescope_2.pdf

4. What is light? Light waves come in many frequencies. The frequency is the number of waves that pass a point in space during any time interval, usually one second. It is measured in units of cycles (waves) per second, or Hertz (Hz). The frequency of visible light is referred to as color, and ranges from 430 trillion Hz, seen as red, to 750 trillion Hz, seen as violet. Again, the full range of frequencies extends beyond the visible spectrum, from less than one billion Hz, as in radio waves, to greater than 3 billion billion Hz, as in gamma rays. http://imagers.gsfc.nasa.gov/ems/waves3.html

5. What is light? The Particle-Wave Duality of Light • 1905 Einstein showed that light can also be explained by a discrete packet of energy • photons • Light has the properties of a wave as well as a particle • this is called the particle-wave duality of light • The relationship between its wavelike and particle-like nature is described as • where E is the energy of the photon and is the wavelength of the EM wave http://www.astro.utoronto.ca/~swlee/ast201spring/ast201_light_telescope_2.pdf

6. Total Internal Reflection Total internal reflection is the reflection of electromagnetic radiation from the interface of medium with larger index of refraction with a medium of smaller index of refraction when making an angle to the normal. Total internal reflection can be used to losslessly redirect a light beam in the direction of its source using a 45°-45°-90° prism. However, there is still an electric field in medium , given by (1) where is the wavenumber in medium 2 and is the critical angle (2) (Bekefi and Barrett 1987, p. 477). Note that this field falls of exponentially with distance z from the interface, and propagates along the interface in the y direction. This disturbance is therefore known as a surface wave and has phase velocity (3) http://scienceworld.wolfram.com/physics/TotalInternalReflection.html

7. Refraction The bending of the normal to the wavefront of a propagating wave upon passing from one medium to another where the propagation velocity is different. The most common example is the refraction of light on passing from air to a liquid, which causes submerged objects to appear displaced from their actual positions. Refraction causes ocean waves to approach shorelines nearly perpendicularly as they reach shallow water and slow down when they "feel" the bottom. Refraction is also the reason that prisms separate white light into its constituent colors. This occurs because different colors (i.e., frequencies) of light travel at different speeds in the prism, resulting in a different amount of deflection of the wavefront for different colors. The amount of refraction can be characterized by a quantity known as the index of refraction, commonly denoted n. The equation specifying the relationship between the angles to the normal in two media is called Snell's law (or sometimes simply the law of refraction). http://scienceworld.wolfram.com/physics/TotalInternalReflection.html

8. Evanescent Wave • An electromagnetic wave observed in • total internal reflection, • undersized waveguides, and in • periodic dielectric heterostructures. While wave solutions have real wavenumbersk, • k for an evanescent mode is purely imaginary. • Evanescent modes are characterized by an exponential attenuation and lack of a phase shift. • Frustrated Total Internal Reflection • If an evanescent wave (such as that produced by total internal reflection) extends across a separating medium into a region occupied by a higher index of refraction material, energy may flow across the boundary. This phenomenon is known as frustrated total internal reflection, and is similar to quantum mechanical tunneling or barrier penetration. When transmission across the boundary occurs in this manner, the "total internal reflection" is no longer total since the transmitted wave comes at the expense of the internally reflected one. http://scienceworld.wolfram.com/physics/EvanescentWave.html

9. SPR - Surface Plasmon Resonance At an interface between two transparent media of different refractive index (glass and water), light coming from the side of higher refractive index is partly reflected and partly refracted. Above a certain critical angle of incidence, no light is refracted across the interface, and total internal reflection is observed. While incident light is totally reflected the electromagnetic field component penetrates a short (tens of nanometers) distance into a medium of a lower refractive index creating an exponentially detenuating evanescent wave. If the interface between the media is coated with a thin layer of metal (gold), and light is monochromatic and p-polarized, the intensity of the reflected light is reduced at a specific incident angle producing a sharp shadow (called surface plasmon resonance) due to the resonance energy transfer between evanescent wave and surface plasmons. The resonance conditions are influenced by the material adsorbed onto the thin metal film. Satisfactory linear relationship is found between resonance energy and mass concentration of biochemically relevant molecules such as proteins, sugars and DNA. The SPR signal which is expressed in resonance units is therefore a measure of mass concentration at the sensor chip surface. This means that the analyte and ligand association and dissociation can be observed and ultimately rate constants as well as equilibrium constants can be calculated. http://www.uksaf.org/tech/spr.html

10. http://www.biotech.iastate.edu/facilities/protein/seminars/BIACore/TechnologyNotes/TechnologyNote1.pdfhttp://www.biotech.iastate.edu/facilities/protein/seminars/BIACore/TechnologyNotes/TechnologyNote1.pdf

11. http://www.biotech.iastate.edu/facilities/protein/seminars/BIACore/TechnologyNotes/TechnologyNote1.pdfhttp://www.biotech.iastate.edu/facilities/protein/seminars/BIACore/TechnologyNotes/TechnologyNote1.pdf

12. http://www.biotech.iastate.edu/facilities/protein/seminars/BIACore/TechnologyNotes/TechnologyNote1.pdfhttp://www.biotech.iastate.edu/facilities/protein/seminars/BIACore/TechnologyNotes/TechnologyNote1.pdf

13. The wavevector of the plasmon wave, Ksp, depends on the refractive indices of the conductor, ngold, (being a constant complex number) and the sample medium, n2, as ksp, = (2 *  / wavelength) * ( ngold2 * n22 / ( ngold2 + n2))0.5. In both expressions the wavelength is the value for the light wave in vacuum. Thus, an increased refractive index of the sample, n2, penetrated by the plasmon enhanced evanescent field increases the wavevector of the plasmon wave. The wavevector of the light kx can be tuned to equate the plasmon wavevector by varying either the angle of incidence, , or the wavelength of the light. http://www.biotech.iastate.edu/facilities/protein/seminars/BIACore/TechnologyNotes/TechnologyNote1.pdf

14. For plasmon excitation by a photon to take place the energy and momentum of these “quantum-particles” must both be conserved during the photon “transformation” into a plasmon. This requirement is met when the wavevector for the photon and plasmon are equal in magnitude and direction for the same frequency of the waves (the wavevector is a parameter in the mathematical formula for the electromagnetic wave related to the momentum). The direction of the wavevector is the direction of the wave propagation (i.e. the light ray direction), while its magnitude depends on the refractive indices of the media that the electromagnetic field wave interacts with along its propagation path. Since the wave vector of the plasmon wave is bound to the conductor surface, it is the (2 *  / wavelength) * n1 * sin () of the incident light which is parallel to the conductor surface that can be equal to the wave-vector of the surface plasmons (ksp, kx) . http://www.biotech.iastate.edu/facilities/protein/seminars/BIACore/TechnologyNotes/TechnologyNote1.pdf

15. http://www.biotech.iastate.edu/facilities/protein/seminars/BIACore/TechnologyNotes/TechnologyNote1.pdfhttp://www.biotech.iastate.edu/facilities/protein/seminars/BIACore/TechnologyNotes/TechnologyNote1.pdf

16. Plasmon Resonance • On the surface of a metal, the electrons behave like waves, not particles, and these waves ripple around on the surface of metals, called " surface plasmons". • If the frequency of the light hitting the metal somehow matched the resonant frequency of the surface plasmons, the surface plasmons begin to resonate. So the incoming light was being absorbed by these strange waves on the surface of metals. excitation = plasmon resonance http://www.ece.rice.edu/~halas/articles/NewSciPlasmonArticle.pdf

17. Plasmon Resonance • In metal nanoparticles, surface plasmons compress electromagnetic energy into very tiny volume. Therefore, the plasmon resonance frequency is dependent not only on the type of metal, but also on its size and shape. Strong optical resonance of metal nanoparticles http://www.ece.rice.edu/muri/slides/sld004.htm

18. Plasmon Resonance Plasmon resonances give to specific metallic nanoparticles a strong and well defined color. This effect was already used in the Middle Ages to fabricate stained-glass windows (left) and Greek vase (right). http://www.ifh.ee.ethz.ch/~martin/res50.en.html

19. http://www.msm.cam.ac.uk/mmc/publications/dr_jap_02.pdf

20. http://www.msm.cam.ac.uk/mmc/publications/dr_jap_02.pdf

21. http://www.msm.cam.ac.uk/mmc/publications/dr_jap_02.pdf

22. http://www.msm.cam.ac.uk/mmc/publications/dr_jap_02.pdf

23. Metallic Nanoshells dielectric core A metal nanoshell is a composite nanoparticle that consists of a dielectric core surrounded by a thin metal shell metal shell http://www.ece.rice.edu/~halas/research/ARO_files/frame.htm

24. Metallic Nanoshells Concentric Sphere Geometry: Metal Nanoshells http://www.ece.rice.edu/muri/slides/sld005.htm

25. Metallic Nanoshells Plasmon Resonance of Gold-Silica Nanoshells can be Tuned Throughout Visible and IR Spectrum http://www.ece.rice.edu/muri/slides/sld006.htm

26. Metallic Nanoshells Solutions of metal nanoshells take on colors depending on the core and radius of the shells. The vial on the left contains solid-gold colloid, while the vial on the right has IR-absorbing nanoshells that appear transparent in visible light. http://oemagazine.com/fromTheMagazine/dec01/pdf/tinybutmighty.pdf

27. Metallic Nanoshells Fabrication Approach to construct the metal nanoshell particles combines techniques of molecular self-assembly with the reduction chemistry of metal colloid synthesis. http://www.ece.rice.edu/~halas/articles/OPN8-02.pdf

28. Metallic Nanoshells Fabrication http://www.ece.rice.edu/~halas/articles/OPN8-02.pdf

29. Metallic Nanoshells Fabrication http://www.ece.rice.edu/muri/slides/sld009.htm

30. Metallic Nanoshells Fabrication http://www.ece.rice.edu/muri/slides/sld010.htm

31. Application of Metallic Nanoshells • The advantages of metal nanoshells enable a broad range of applications, especially in bio-medicine area. • Nanoshells are made of gold colloid and reduced gold, which have demonstrated good biocompatibility http://www.ece.rice.edu/~halas/articles/nmat891.pdf

32. Application of Metallic Nanoshells • Nanoshells are stable in solution, injectable, small enough to flow through circulatory system • Gold nanoshells demonstrate strong optical properties in the near infrared region. http://www.ece.rice.edu/~halas/articles/nmat891.pdf

33. Application of Metallic Nanoshells Nanoshells as Cancer Therapy The most useful nanoshells are those that absorb near-infrared light, which can easily penetrate several centimeters of human tissue. The absorption of light by the nanoshells creates an intense heat that is lethal to cells. http://press2.nci.nih.gov/sciencebehind/nanotech/nano18.htm

34. Application of Metallic Nanoshells Nanoshells as Cancer Therapy Researchers can already link nanoshells to antibodies that recognize cancer cells. These nanoshells seek out their cancerous targets, then applying near-infrared light. In laboratory cultures, the heat generated by the light-absorbing nanoshells has successfully killed tumor cells while leaving neighboring cells intact. http://press2.nci.nih.gov/sciencebehind/nanotech/nano19.htm

35. Application of Metallic Nanoshells Nanoshells asDrug delivery Reversible Collapse As a Result of Repetitive Near IR Irradiation Thermoresponsive polymer collapses reversibly at elevated temperatures http://www.ece.rice.edu/~halas/articles/OPN8-02.pdf

36. Application of Metallic Nanoshells Nanoshells asDrug delivery • Thermoresponsive polymer containing optically active nanoparticles • Load polymer with drug, then implant into patient • Irradiate with near IR laser to heat nanoparticles • Polymer collapses, releasing drug http://www.ece.rice.edu/~halas/research/SershenMURI_files/frame.htm

37. total time: ~2 days additional purification sample purified sample optical testing total time: ~20 seconds sample infrared testing Application of Metallic Nanoshells Nanoshells asRapid Immunoassays in Blood and Tissue Nanoshells can greatly speed up diagnoses, because they can have spectral emissions in the infrared region, rendering the purification step unnecessary. http://www.ece.rice.edu/~halas/research/WestMURI_files/frame.htm

38. Conclusion • Metal Nanoshells are a breakthrough technology that offers precise control of optical properties over much of the visible and infrared portions of the spectrum. • The environmentally friendly, biocompatible aspects of metal nanoshells enable a broad range of applications