page_title: Localized surface plasmon
section_title: Applications
hierarchical_section_title: Localized surface plasmon / Applications
caption_attribution_description: False color scanning electron micrograph (250,000 times magnification) showing the gold nanoparticles created by NIST and the National Cancer Institute's Nanotechnology Characterization Laboratory (NCL) for use as reference standards in biomedical research laboratories. Credit: Andras Vladar, NIST Disclaimer: Any mention of commercial products within NIST web pages is for information only; it does not imply recommendation or endorsement by NIST. Use of NIST Information: These World Wide Web pages are provided as a public service by the National Institute of Standards and Technology (NIST). With the exception of material marked as copyrighted, information presented on these pages is considered public information and may be distributed or copied. Use of appropriate byline/photo/image credits is requested.
context_page_description: A localized surface plasmon is the result of the confinement of a surface plasmon in a nanoparticle of size comparable to or smaller than the wavelength of light used to excite the plasmon. When a small spherical metallic nanoparticle is irradiated by light, the oscillating electric field causes the conduction electrons to oscillate coherently. When the electron cloud is displaced relative to its original position, a restoring force arises from Coulombic attraction between electrons and nuclei. This force causes the electron cloud to oscillate. The oscillation frequency is determined by the density of electrons, the effective electron mass, and the size and shape of the charge distribution. The LSP has two important effects: electric fields near the particle's surface are greatly enhanced and the particle's optical absorption has a maximum at the plasmon resonant frequency. Surface plasmon resonance can also be tuned based on the shape of the nanoparticle. The plasmon frequency can be related to the metal dielectric constant. The enhancement falls off quickly with distance from the surface and, for noble metal nanoparticles, the resonance occurs at visible wavelengths.
context_section_description: The plasmon resonant frequency is highly sensitive to the refractive index of the environment; a change in refractive index results in a shift in the resonant frequency. As the resonant frequency is easy to measure, this allows LSP nanoparticles to be used for nanoscale sensing applications. Also, nanoparticles exhibiting strong LSP properties, such as gold nanorods, could enhance the signal in surface plasmon resonance sensing. Nanostructures exhibiting LSP resonances are used to enhance signals in modern analytical techniques based on spectroscopy. Other applications that rely on efficient light to heat generation in the nanoscale are heat-assisted magnetic recording (HAMR) , photothermal cancer therapy, and thermophotovoltaics. So far, high efficiency applications using plasmonics have not been realized due to the high ohmic losses inside metals especially in the optical spectral range (visible and NIR)., Additionally surface plasmons have been used to create super lenses, invisibility cloaks, and to improve quantum computing. Another interesting area of research in plasmonics is the ability to turn plasmons "on" and "off" via modification of another molecule. The ability to turn plasmons on and off has important consequences for increasing sensitivity in detection methods. Recently, a supramolecular chromophore was coupled with a metal nanostructure. This interaction changed the localized surface plasmon resonance properties of the silver nanostructure by increasing the absorption intensity.  
caption: Gold nanoparticles, pictured here under scanning electron microscope, exhibit strong LSP resonances.
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