Surface plasmon resonance (SPR).

Surface plasmon resonance (SPR) can be described as the resonant, collective oscillation of valence electrons in a solid stimulated by incident light. The resonance condition is established when the frequency of light photons matches the natural frequency of surface electrons oscillating against the restoring force of positive nuclei. SPR in nanometer-sized structures is called localized surface plasmon resonance.

SPR 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 the fundamental principle behind many color-based biosensor applications and different lab-on-a-chip sensors.

Explanation[link]

Surface plasmons, also known as surface plasmon polaritons, are surface electromagnetic waves that propagate in a direction parallel to the 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.

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 frequency-dependent relative permittivity between the external medium and the surface. This quantity, hereafter referred to as the materials' "dielectric constant," is complex-permittivity. In order for the terms which describe the 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).

LSPRs (Localized SPRs) are collective electron charge oscillations in metallic nanoparticles that are excited by light. They exhibit enhanced near-field amplitude at the resonance wavelength. This field is highly localized at the nanoparticle and decays rapidly away from the nanoparticle/dieletric interface into the dielectric background, though far-field scattering by the particle is also enhanced by the resonance. Light intensity enhancement is a very important aspect of LSPRs and localization means the LSPR has very high spatial resolution (subwavelength), limited only by the size of nanoparticles. Because of the enhanced field amplitude, effects that depend on the amplitude such as magneto-optical effect are also enhanced by LSPRs.^[1][2]

Realization[link]

Otto configuration

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 its momentum to that of the plasmon. In the case of p-polarized light (polarization occurs parallel to the plane of incidence), this is possible by passing the light through a block of glass to increase the wavenumber (and the momentum), and achieve the resonance at a given wavelength and angle. S-polarized light (polarization occurs perpendicular to the plane of incidence) cannot excite electronic surface plasmons. Electronic and magnetic surface plasmons obey the following dispersion relation:

Failed to parse (Missing texvc executable; please see math/README to configure.): K(\omega) = \frac{\omega}{c} \sqrt{\frac{\varepsilon_1 \varepsilon_2 \mu_1 \mu_2}{\varepsilon_1 \mu_1 + \varepsilon_2 \mu_2}}

where Failed to parse (Missing texvc executable; please see math/README to configure.): \epsilon

is the dielectric constant, and Failed to parse (Missing texvc executable; please see math/README to configure.): \mu
is the magnetic permeability of the material (1: the glass block, 2: the metal film).

Typical metals that support surface plasmons are silver and gold, but metals such as copper, titanium or chromium have also been used.

When using light to excite SP waves, there are two configurations which are well known. In the Otto setup, the light illuminates the wall of a glass block, typically a prism, and is totally internally reflected. A thin metal film (for example gold) is positioned close enough to the prism wall so that an evanescent wave can interact with the plasma waves on the surface and hence excite the plasmons.

In the Kretschmann configuration, the metal film is evaporated onto the glass block. The light again illuminates the glass block, 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.

SPR emission[link]

When the surface plasmon wave interacts with a local particle or irregularity, such as a rough surface, part of the energy can be re-emitted as light. This emitted light can be detected behind the metal film from various directions.

Applications[link]

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 molecular adsorption, such as polymers, DNA or proteins, etc. Technically, it is common, that the angle of the reflection minimum (absorption maximum) is measured. This angle changes in the order of 0.1° during thin (about nm thickness) film adsorption. (See also the Examples.) In other cases the changes in the absorption wavelength is followed.^[3] The mechanism of detection is based on that the adsorbing molecules cause changes in the local index of refraction, changing the resonance conditions of the surface plasmon waves.

If the surface is patterned with different biopolymers, using adequate optics and imaging sensors (i.e. a camera), the technique can be extended to surface plasmon resonance imaging (SPRI). This method provides a high contrast of the images based on the adsorbed amount of molecules, somewhat similar to Brewster angle microscopy (this latter is most commonly used together with a Langmuir-Blodgett trough).

For nanoparticles, localized surface plasmon oscillations can give rise to the intense colors of suspensions or sols containing the nanoparticles. Nanoparticles or nanowires of noble metals exhibit strong absorption bands in the ultraviolet-visible light regime that are not present in the bulk metal. This extraordinary absorption increase has been exploited to increase light absorption in photovoltaic cells by depositing metal nanoparticles on the cell surface.^[4] The energy (color) of this absorption differs when the light is polarized along or perpendicular to the nanowire.^[5] Shifts in this resonance due to changes in the local index of refraction upon adsorption to the nanoparticles can also be used to detect biopolymers such as DNA or proteins. Related complementary techniques include plasmon waveguide resonance, QCM, extraordinary optical transmission, and dual polarization interferometry

Data interpretation[link]

The most common data interpretation is based on the Fresnel formulas, which treat the formed thin films as infinite, continuous dielectric layers. This interpretation may result multiple possible refractive index and thickness values. However, usually only one solution is within the reasonable data range.

Metal particle plasmons are usually modeled using the Mie scattering theory.

In many cases no detailed models are applied, but the sensors are calibrated for the specific application, and used with interpolation within the calibration curve.

Examples[link]

Layer-by-layer self-assembly[link]

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 (and refractive index) of adsorbed self-assembled nanofilms on gold substrates. The resonance curves shift to higher angles as the thickness of the adsorbed film increases. This example is a 'static SPR' measurement.

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[link]

Association and dissociation signal

Example of output from Biacore

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.

For this, a so-called bait ligand is immobilized on the dextran surface of the SPR crystal. Through a microflow system, a solution with the prey analyte is injected over the bait layer. As the prey analyte binds the bait ligand, an increase in SPR signal (expressed in response units, RU) is observed. After desired association time, a solution without the prey analyte (usually the buffer) is injected on the microfluidics that dissociates the bound complex between bait ligand and prey analyte. Now as the prey analyte dissociates from the bait ligand, a decrease in SPR signal (expressed in resonance units, RU) is observed. From these association ('on rate', k_a) and dissociation rates ('off rate', k_d), the equilibrium dissociation constant ('binding constant', K_D) 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;

Failed to parse (Missing texvc executable; please see math/README to configure.): K_D = \frac{k_{\text{d}}}{k_{\text{a}}}

Magnetic plasmon resonance[link]

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.

See also[link]

• Waves in plasmas
• plasmon
• Spinplasmonics
• Hydrogen sensor
• Nano-optics

References[link]

Further reading[link]

External links[link]

• The affinity and valence of an antibody can be determined by equilibrium dialysis (ncbi.nlm.nih.gov)

Ken Block
Ken Block in 2008.
Nationality	American
Born	(1967-11-21) 21 November 1967 (age 44) Long Beach, California
2012 Rally America
Debut season	2005
Current team	Monster World Rally Team
Best finish	2nd Overall in Rally America in 2006 and 2008
Awards
2004[1] 2005[1] 2009	• One of the most influential people (#17) in Sports Business Journal • Ad Age's Marketing 50 • One of the Fast 50 in Fast Company Magazine • 40 Under 40 Awards, Sports Business Journal • Rally America's Rookie of the Year • Gymkhana 2 was 2009's #4 most viewed viral video

Ken Block (born November 21, 1967, in Long Beach, California)^[2] is a professional rally driver with the Monster World Rally Team. Block is also one of the co-founders and recently appointed Chief Brand Officer of DC Shoes.^[1] Block has also competed in many action sports events including skateboarding, snowboarding, and motocross.

Rallying[link]

2005[link]

In 2005, Ken Block began his national rallying career with the Vermont SportsCar team.^[3] Vermont SportsCar prepared a 2005 Subaru WRX STi for Block to compete. His first event of the rallying season was Sno*Drift, where he ended up finishing seventh overall and fifth in the Group N class.^[4] During the 2005 season, Block had five top five finishes and placed third overall in the Group N class and fourth overall in the Rally America National Championship.^[3] At the end of his first rallying year, Ken Block had won the Rally America Rookie of the Year award.^[5]

2006[link]

In 2006, Ken Block along with his DC rally teammate Travis Pastrana signed a new sponsorship deal with Subaru.^[3] Through this deal with Subaru, the teammates became known as "Subaru Rally Team USA."^[3] With the new rally season, Block also got a brand new Vermont SportsCar prepped 2006 Subaru WRX STi.^[3] He competed in the first ever X Games rally event at X Games XII.^[3] In the competition, Block ended up finishing third to take the bronze.^[3] He went on to compete in the 2006 Rally America National Championship, where he finished second overall.^[3]

2007[link]

In 2007, Ken Block competed in the X Games XIII rally event, where he placed second overall and won a silver medal.^[5] In the 2007 Rally America National Championship, Block finished third overall.^[5] During this season, Block also entered in a few rounds of the World Rally Championship; Rally Mexico and Rally New Zealand.^[4] In Rally New Zealand, Block recorded two top-five stage times in the Group N class.^[4] At the end of 2007, Block had achieved 19 podiums and 8 overall victories in rally events.^[1]

2008[link]

In 2008, Block was provided with a brand new rally prepped 2008 Subaru WRX STi to compete. Block decided to compete in the Rallye Baie-des Chaleurs of the Canadian Rally Championship to gain some experience with his new 2008 rally car and prepare for the World Rally Championships later this year.^[6] Block gained his first Canadian rally win at the event.^[6] This was only the second event for the new car.^[6] Block and his co-driver were unable to get any championship points at the event due to not having a Canadian competition license.^[6] Block competed in the Rally New York USA competition and finished in first place.^[7] In the X Games XIV rally competition, Block finished tied for third place with Dave Mirra.^[8] This occurrence was due to both competitors having issues with their car. Block, who made it to the semi-finals of the event, had a radiator problem after landing the car awkwardly on a jump. With both bronze place competitors in damaged cars unable to compete, the medals were awarded to both of them.^[8]

Block competed in the 2008 Rally America National championship, which concluded on October 17, 2008. In the event, he finished second overall with a strong victory in the last event. In the Lake Superior Performance Rally stage, Block finished over one minute ahead of his next closest competitor and secured the second overall position.^[9] Next up for Block this rally season is three World Rally Championship events.^[4]

2009[link]

Block appeared in a segment of motoring show Top Gear.^[10]

2010[link]

Ken Block testing Ford Fiesta for the 2010 Rally America season

Block driving a Ford Focus RS WRC at the 2010 Rallye de France

On January 6, 2010 the Monster World Rally Team announced Ken as their driver for selected rounds of the World Rally Championship, in which he will be campaigning the Monster/Ford Racing Focus RS WRC 08. His car will be prepared and run by the North of England based M-Sport, who also prepare the official Ford WRC cars. He will be simultaneously running in his sixth season of the Rally America Championship in an open class Ford Fiesta, as well as his fifth X-games. Ken will also be the first ever American driver to campaign for the World Rally Championship. On February 27, Block won the Rally in the 100 Acre Wood (Rally America) for the 5th consecutive time. This broke the record held by John Buffum.^[11] Ken is currently being trained by former Ford factory driver Markko Märtin. At the Spain rally, he won his first 2 points in World Rally Championship.

2011[link]

On March 23, Block and his co-driver Alex Gelsomino were taken to hospital, having rolled their Ford Fiesta RS WRC during the shakedown stage of the 2011 Rally de Portugal in Faro, Portugal.^[12] A representative of the Monster World Rally team later stated that both men were fine.^[13]

Complete Rally America results[link]

(key)

Complete WRC results[link]

* Season in progress.

PWRC results[link]

Other motorsport activities[link]

On October 15, 2009, it was reported that Block was close to a deal to join the World Rally Championship in a new Ford team. Long time co-driver Alex Gelsomino is also reportedly involved in the deal. Former Subaru WRC driver Chris Atkinson has been reported to be lined up as Block's team-mate in the all-new Monster Energy Drink Ford World Rally Team.^[14]

In 2005, Ken Block along with his DC Shoes associates participated in the Gumball 3000 Rally. For the event they sent out three modified 2004 Subaru WRX STi's sponsored by DC Shoes.^[15][16]

In 2006, Ken Block competed in the One Lap of America competition along with Brian Scotto. They were teamed up in a 2006 Subaru WRX STi and finished forty-fifth overall.^[17]

In 2006, for the Discovery Channel show Stunt Junkies, Ken Block jumped his Subaru WRX STi rally car 171 feet (52 m) and a max height of 25 feet (7.6 m).^[3] The whole episode was dedicated to Ken Block attempting this stunt.

In 2007, Ken Block joined the DC Shoes Snowboarding team at New Zealand's Snow Park.^[3] Block did massive jumps and assisted in snowboarding tricks while driving his rally car on the mountain alongside the snowboarders. The session made the cover of the December 2007 issue of Snowboarder Magazine and closed out the MTN.LAB 1.5 DVD.^[3]

In 2009, for the BBC show Top Gear, Ken took James May out for Gymkhana-style driving at Block's stunt course at Inyokern Airport, an operational California airport, also starring Ricky Carmichael, whom Ken describes as 'a good friend'.

In 2010, for the BBC show Top Gear, Ken took the feature car from the previous episode (a Reliant Robin) for a lap of the Top Gear test track. He rolled the car and was unable to complete a lap but was unhurt.

On January 6, 2010, the announcement is made as Ken joins up with Ford and begins his WRC career driving both a Ford Fiesta and Focus RS WRC.

On August 24, 2010, Block released the first of a three part Gymkhana 3 video release featuring his new Ford Fiesta.^[18]

Ken Block also holds the world record for the world's fastest snow cat, a modified Subaru STI called a Trax STI.^{[citation needed]}

On September 14, 2010, Block's third Gymkhana video, featuring a Ford Fiesta, was released on YouTube.^[19] The video got more than seven million views in its first week.

On August 16, 2011, the fourth Gymkhana video, The Hollywood Megamercial was released on YouTube, featuring Block driving around the Universal Studios backlot.^[20]

Involvement In Colin McRae: Dirt 2 and Dirt 3[link]

Ken Block is featured as a driver in Codemasters Colin McRae: Dirt 2, along with his Subaru Rally Team USA Impreza.
In Dirt 3 he is seen as a driver and Gymkhana teacher, his Monster World Rally Team vehicles are available in the game.

References[link]

External links[link]

Wikimedia Commons has media related to: Ken Block

• Ken Block's Official site
• Monster World Rally Team
• Rally Results and News
• Subaru Rally Team USA
• Rally America Website
• Ken Block Official Merchandise Store
• Ken Block Interview
• Gymkhana racing improved by Ken Block, Video, ~4min
• dirt2game.com