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The excitation of surface plasmons by light is denoted as a surface plasmon resonance (SPR) for planar surfaces or localized surface plasmon resonance (LSPR) for nanometer-sized metallic structures. In physics, the plasmon is the quasiparticle resulting from the quantization of plasma oscillations just as photons and phonons are quantizations of light and sound waves, respectively. ...
This phenomenon is the basis of many standard tools for measuring adsorption of material onto planar metal (typically gold and silver) surfaces or onto the surface of metal nanoparticles. It is behind many color based biosensor applications and different lab-on-a-chip sensors. Adsorption is a process that occurs when a gas or liquid solute accumulates on the surface of a solid or, more rarely, a liquid (adsorbent), forming a molecular or atomic film (the adsorbate). ...
It has been suggested that nanopowder be merged into this article or section. ...
A biosensor is a device for the detection of an analyte that combines a biological component with a physicochemical detector component. ...
This article is about the technology. ...
Explanation Surface plasmons, also known as surface plasmon polaritons, are surface electromagnetic waves that propagate parallel along a metal/dielectric (or metal/vacuum) interface. Since the wave is on the boundary of the metal and the external medium (air or water for example), these oscillations are very sensitive to any change of this boundary, such as the adsorption of molecules to the metal surface. This article is in need of attention. ...
A dielectric, or electrical insulator, is a substance that is highly resistant to electric current. ...
To describe the existence and properties of surface plasmons, one can choose from various models (quantum theory, Drude model , etc.). The simplest way to approach the problem, is to treat each material as a homogeneous continuum, described by a dielectric constant. With the terms of this description for electronic surface plasmons to exist, the real part of the dielectric constant of the metal must be negative and its magnitude must be greater than that of the dielectric. This condition is met in the IR-visible wavelength region for air/metal and water/metal interfaces (where the real dielectric constant of a metal is negative and that of air or water is positive). The Drude model of electrical conduction was developed in the 1900s by Paul Drude to explain the transport properties of electrons in materials (especially metals). ...
Realisation
 Kretschmann configuration In order to excite surface plasmons in a resonant manner, one can use an electron or light beam (visible and infrared are typical). The incoming beam has to match with its impulse to that of the plasmon. In the case of p-polarized light, this is possible by passing the light through a block of glass to increase the wavenumber (and the impulse), and achieve the resonance at a given wavelength and angle. S-polarized light can not excite electronic surface plasmons. Image File history File links No higher resolution available. ...
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Image File history File links Size of this preview: 800 × 489 pixelsFull resolution (873 × 534 pixel, file size: 55 KB, MIME type: image/png) Scheme of SPR setup. ...
Image File history File links Size of this preview: 800 × 489 pixelsFull resolution (873 × 534 pixel, file size: 55 KB, MIME type: image/png) Scheme of SPR setup. ...
The items in the Metroid series are the driving force behind its gameplay. ...
In classical mechanics, the impulse of a constant force is the product of the force and the time during which it acts. ...
In electrodynamics, polarization (also spelled polarisation) is the property of electromagnetic waves, such as light, that describes the direction of their transverse electric field. ...
Wavenumber in most physical sciences is a wave property inversely related to wavelength, having SI units of reciprocal meters (m−1). ...
In classical mechanics, the impulse of a constant force is the product of the force and the time during which it acts. ...
In electrodynamics, polarization (also spelled polarisation) is the property of electromagnetic waves, such as light, that describes the direction of their transverse electric field. ...
Electronic and magnetic surface plasmons obey the following dispersion relation: The relation between the energy of a system and its corresponding momentum is known as its dispersion relation. ...
 Typical metals that support surface plasmons are silver and gold, but metals such as copper, titanium, or chromium can also support surface plasmon generation.
Using light to excite SP waves, there are two constructions which are well known. In the Otto setup, the light is shone on the wall of a glass block, typically a prism, and totally reflected. A thin metal (for example gold) film is positioned close enough, that the evanescent waves can interact with the plasma waves on the surface and excite the plasmons. The larger the angle to the normal, the smaller is the fraction of light transmitted, until the angle when total internal reflection occurs. ...
An evanescent wave is an electromagnetic wave that decays exponentially with distance. ...
In the Kretschmann configuration, the metal film is evaporated onto the glass block. The light is again illuminating from the glass, and an evanescent wave penetrates through the metal film. The plasmons are excited at the outer side of the film. This configuration is used in most practical applications.
Applications Surface plasmons have been used to enhance the surface sensitivity of several spectroscopic measurements including fluorescence, Raman scattering, and second harmonic generation. However, in their simplest form, SPR reflectivity measurements can be used to detect DNA or proteins by the changes in the local index of refraction upon adsorption of the target molecule to the metal surface. If the surface is patterned with different biopolymers, the technique is called Surface Plasmon Resonance Imaging (SPRI). Fluorescence induced by exposure to ultraviolet light in vials containing various sized Cadmium selenide (CdSe) quantum dots. ...
Raman scattering or the Raman effect is the inelastic scattering of a photon. ...
Second Harmonic Generation (SHG) is a subcategory of nonlinear optics in physics. ...
For nanoparticles, localized surface plasmon oscillations can give rise to the intense colors of solutions of plasmon resonance nanoparticles and/or very intense scattering. Nanoparticles of noble metals exhibit strong ultraviolet-Visible absorption bands that are not present in the bulk metal. Shifts in this resonance due to changes in the local index of refraction upon adsorption of biopolymers to the nanoparticles can also be used to detect biopolymers such as DNA or proteins. Related complimentary techniques include plasmon waveguide resonance, QCM and Dual Polarisation Interferometry It has been suggested that nanopowder be merged into this article or section. ...
Scattering is a general physical process whereby some forms of radiation, such as light, sound or moving particles, for example, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which it passes. ...
For other uses, see Ultraviolet (disambiguation). ...
The optical spectrum (light or visible spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. ...
An absorption band is a range of wavelengths (or, equivalently, frequencies) in the electromagnetic spectrum within which electromagnetic energy is absorbed by a substance. ...
A quartz crystal microbalance (QCM) measures mass by measuring the change in frequency of a piezoelectric quartz crystal when it is disturbed by the addition of a small mass such as a virus or any other tiny object intended to be measured. ...
This article, image, template or category should belong in one or more categories. ...
Examples
 SPR curves measured during the adsorption of a polyelectrolyte and then a clay mineral self-assembled film onto a thin (ca. 38 nanometers) gold sensor. One of the first common applications of surface plasmon resonance spectroscopy was the measurement of the thickness of adsorbed self-assembled nanofilms on gold substrates. An example is presented in 'figure' The resonance curves shift to higher angles as the thickness of the adsorbed film increases. This example is a 'static SPR' measurement. Self-assembly is the fundamental principle which generates structural organization on all scales from molecules to galaxies. ...
Image File history File links No higher resolution available. ...
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Polyelectrolytes combine the properties of electrolytes (salts) and polymers (high MW compounds). ...
For other uses, see Clay (disambiguation). ...
When higher speed observation is desired, one can select an angle right below the resonance point (the angle of minimum reflectance), and measure the reflectivity changes at that point. This is the so called 'dynamic SPR' measurement. The interpretation of the data assumes, that the structure of the film does not change significantly during the measurement.
Binding constant determination
 Association and dissociation signal When the affinity of two ligands has to be determined, the binding constant must be determined. It is the equilibrium value for the product quotient. This value can also be found using the dynamical SPR parameters and, as in any chemical reaction, it is the association rate divided by the dissociation rate. Image File history File links Size of this preview: 800 × 554 pixelsFull resolution (869 × 602 pixel, file size: 7 KB, MIME type: image/png) Simulation of association and dissociation SPR signal using MATLAB software. ...
Image File history File links Size of this preview: 800 × 554 pixelsFull resolution (869 × 602 pixel, file size: 7 KB, MIME type: image/png) Simulation of association and dissociation SPR signal using MATLAB software. ...
Image File history File links Size of this preview: 800 × 390 pixelsFull resolution (876 × 427 pixel, file size: 53 KB, MIME type: image/jpeg) Output from Biacore, with four different concentrations of the same protein. ...
Image File history File links Size of this preview: 800 × 390 pixelsFull resolution (876 × 427 pixel, file size: 53 KB, MIME type: image/jpeg) Output from Biacore, with four different concentrations of the same protein. ...
Biacore is a life science products company, based in Sweden specializing in measuring protein-protein interaction and binding affinity. ...
In chemistry, a ligand is an atom, ion, or molecule (see also: functional group) that generally donates one or more of its electrons through a coordinate covalent bond to, or shares its electrons through a covalent bond with, one or more central atoms or ions (these ligands act as a...
The binding constant is a special case of the equilibrium constant K. The equilibrium state of molecular binding, i. ...
For this, a so-called bait ligand is coated to the gold surface of the SPR crystal. Through a microflow system, a solution with the prey ligand can flow over the bait layer and bind. Binding will make the SPR signal change to an equilibrium. After some time, a solution without the prey is applied, and a new equilibrium will be reached. From these association ('on rate', von) and dissociation speeds ('off rate', voff), the binding constant can be calculated.
The actual SPR signal can be explained by the electromagnetic 'coupling' of the incident light with the surface plasmon of the gold layer. This plasmon can be influenced by the layer just a few nanometer across the gold-solution interface i.e. the bait protein and possibly the prey protein. Binding makes the reflection angle change.;
Data Processing for measuring binding affinity 1) Zeroing: zero on the y-axis for start time of the injection; 2) Reference subtraction: sunstract-out data from the reference spots; 3) Replication overlays and double Referencing; 4) Globally fitting data: numerically fit the data to 1:1 interaction model.
Possible artifacts while measuring binding affinity 1) Spikes in the sensogram in the response to elevated temperatures that can occur due to outgassing of the buffer; 2) excluded-volume effects; 3) Protein immobilization affects affinity; 4) the injected analyte is not monomeric (use analytical ultracentrifugation to assure monomeric state), aggregation; 5) avidity effects; 6) both analyte and ligand should be chemically and conformationaly pure; 7) instrument is not clean and should be primed; 8) baseline drift; 9) check for non-specific binding; 10) surface heterogeniety; 11) surface instability; 12) mass-transport effects, check for k_on and k_off dependence on flow rate; 13) one cannot measure association or dissociation rates which are faster than the machine sampling frequency (usually 1 Hz); 14) If your concentrations are wrong then your affinity results would be wrong [concentration of correctly folded protein]; 15) If your protein Lysine content is high you might consider conjugating the protein by a method other than amine chemistry [biotin is recommended]; 16) degradarion of the protein on the chip during long measurements (several hours); 17) Biphasic sensogram is bad; lower concentration to achieve a monotonic curve of association and dissociation.
Validation of measuring binding affinity 1) Isothermal titration calorimetry; 2) Nuclear magnetic resonance; 3) using different machine (Biacore vs. ProteOn); 4) co-immunoprecipitation (less quantitative)
Tips for acheiving a good measurment of binding affinity 1) To avoid using to much protein inject a small amount of sample only for a short time [even if you don't reach a steady-state]. That will help avoiding aggregation effects; 2) If the two binding partners are protein and short peptide, congugate the peptide to the surface. Otherwise, several peptides would bind a single protein in mixed specific and non-specific binding; 3) Add 1% alignate top the buffer to reduce non-specific association; 4) protein must be fresh (i.e., not frosen), after gel-filtration, and kept on ice; 5) use as a reference measurement "empty but activated" surface; 6) chi-squared should be lower than 10% of Rmax.
Magnetic Plasmon Resonance Recently, there has been an interest in magnetic surface plasmons. These require materials with large negative magnetic permeability, a property that has only recently been made available with the construction of metamaterials. A metamaterial (or meta material) is a material that gains its properties from its structure rather than directly from its composition. ...
References - (1988) Surface plasmons on smooth and rough surfaces and on gratings. Springer Verlag, Berlin. ISBN 978-3540173632.
- Stefan Maier (2007). Plasmonics: Fundamentals and Applications. Springer. ISBN 978-0387331508.
- Hutter E, Fendler J. Exploitation of Localized Surface Plasmon Resonance. Adv. Mater. 2004, 16, 19, 1685-1706.
- Aslan K, Lakowicz JR, Geddes C. Plasmon light scattering in biology and medicine: new sensing approaches, visions and perspectives. Current Opinion in Chemical Biology 2005, 9:538–544
- Smith EA, Corn RM. Surface Plasmon Resonance Imaging as a Tool to Monitor Biomolecular Interactions in an Array Based Format. Appl. Spectroscopy, 2003, 57, 320A-332A.
- J. N. Gollub, D. R. Smith, D. C. Vier, T. Perram, J. J. Mock, Phys. Rev. B 71, 195402 (2005)
- http://www.astbury.leeds.ac.uk/facil/SPR/spr_intro2004.htm (a short detailed synopsis of how surface plasmon resonance works in practice)
External links - The affinity and valence of an antibody can be determined by equilibrium dialysis (ncbi.nlm.nih.gov)
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