Gold nanoparticles localized surface plasmon resonance

Long period gratings modified by the deposition of a self-assembled colloid monolayer of gold have been shown to enhance SRI sensitivity, which was attributed to the localized surface plasmon resonance (LSPR) of gold nanoparticles61. The system was used after functionalization of the gold nanoparticles with dini-trophenyl (DNP) antigen, for the detection of anti-(DNP) with a limit of detection as low as 9.5 x 10 10 M. 

A parallel development in sensor technology is the use of gold nanoparticles (AuNPs) and their localized surface plasmon resonances (LSPR) [41] for sensing purposes. Mirkin et al. [42] showed how single nanoparticles (NPs) in solution can... 

Wang TJ, Lin CS (2006) Electro-optically modulated localized surface plasmon resonance biosensors with gold nanoparticles. Appl Phys Lett 89 173903... 

Metal nanoparticles have attracted considerable interest due to their properties and applications related to size effects, which can be appropriately studied in the framework of nanophotonics [1]. Metal nanoparticles such as silver, gold and copper can scatter light elastically with remarkable efficiency because of a collective resonance of the conduction electrons in the metal (i.e., the Dipole Plasmon Resonance or Localized Surface Plasmon Resonance). Plasmonics is quickly becoming a dominant science-based technology for the twenty-first century, with enormous potential in the fields of optical computing, novel optical devices, and more recently, biological and medical research [2]. In particular, silver nanoparticles have attracted particular interest due to their applications in fluorescence enhancement [3-5]. 

A. Prabhakar, S. Mukheiji, A novel C-shaped, gold nanoparticle coated, embedded polymer waveguide for localized surface plasmon resonance based detection. Lab on a Chip 10 (2010) 3422-3425. 

Metal nanoparticles present localized surface plasmon resonances (LSPRs) that are collective excitations of the electrons at the interface between a conductor and a dielectric. The resonant plasma oscillation causes local field enhancement, and this is utilized in SERS [61,62], second-harmonic generation [63], and scanning near-field optical microscopy [64]. In particular, certain metals such as silver and gold have been much studied due to the feet that they present this LSPR in the visible spectral region. 

It is comparatively well known that nanoparticles of gold have a very different color to bulk gold. This is the localized surface plasmon resonance. Localized surface plasmon resonances in gold... 

Figure 2. Calculated localized surface plasmon resonance spectrum of a dimer of hemispherical gold nanoparticles of radius 7 nm and interparticle centre-to-centre distance 17.5 nm. A dielectric coating of n = 1.45 and thickness 1.75 run leads to a second absorption feature at 650 nm.

Localized surface plasmon (LSP) The surface plasmon (SP) cannot propagate on the surface of metallic nanoparticles and therefore, is localized and hence known as localized surface plasmon (LSP). The LSP resonance of gold and silver NPs occurs in the visible range of the spectrum, which makes these two metals particularly useful for a number of applications ranging from ultrasensitive diagnostic tools to biosensing devices. 

LSPs are detected as resonance peaks in the absorption or scattering spectra or as dips in the transmission spectra of the metallic nanoparticles. Nanoparticles of very conductive metals like gold, silver, and copper are ideal materials for excitation of localized surface plasmons due to an extremely high ratio of the modulus of the real (Sr) to the imaginary parts (8i) of its dielectric constant. Silver and copper nanoparticles are prone to oxidation and therefore often require coatings of protective over layers. Gold nanoparticles are chemically stable and are employed for the development of devices based on plasmon resonances of nanoparticles. 

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