Particle plasmon resonance

The branched polysaccharide dextran is assembled with alkanethiol-modified gold nanoparticles and the resulting nanocomposite is then functionalized to facilitate the specific binding of target biomolecules. This biorecognition process can be easily detected by particle plasmon resonance (PPR), based on the optical properties of gold nanoparticles [163]. 

It is also important to notice that plasmon characteristics of particle plasmons typically represent those of single particles, because particles tend to aggregate at high concentration at which interparticle interaction starts to appear for an ensemble of particles and particle plasmon resonance is affected additionally by particle... 

Kotler and Nitzan" applied the electrostatic limit to a silver sphere coated with a dye. They found also in this case a double-peak behavior, under certain circumstances. Noteworthy, are the enhancements of the Raman scattering of up to —10", near the particle plasmon resonance. (For their model of a sphere it is at 3.5 eV but for other shapes it can be brought into the visible range). The enhancement is very weakly dependent on the distance from... 

Clusters composed out of a few atoms are better described and modeled as supra-molecular structures exhibiting no cluster type behavior such as e.g. a well-defined particle plasmon resonance (Figure 3). Ultra-large metal colloids of 300 nm or more exhibit macroscopic behavior such as metallic luster and bulk conductivity (Figure 4). Colloidal structures made up of a plurality of individual clusters are often referred to as mesoscopic systems, cluster matter or nano-crystalline materials. Thus, colloidal particles cover an extreme wide range in size [1,2,3,4]. 

The excitation of the dipole particle plasmon resonance provides the theoretical basis for the development of the electromagnetic enhancement mechanism (EM). ... 

The basic problem of nonlocal theories is to find an appropriate e(,k,co). Several authors have dealt with this problem for both geometries, a dipole above a surface and a dipole close to a metal nanoparticle.It is certainly beyond the scope of this chapter to go into detail of those theories. However, let us briefly note that the results are miscellaneous. For example, in the case of a dipole close to a metal nanosphere, Leung predicts one to two orders of magnitude less energy transfer to the nanoparticle in the case where the dipolar transition is energetically lower than the particle plasmon resonance. Ekardt and Penzar predict exactly the opposite. 

Figure 7 (a) Time resolved luminescence signal from a pure gold nanoparticle sc ution. (b) spectrally resolved signal within the first 5 ps. A pronounced Raman signal at 430 nm and a weak emission following the particle plasmon resonance are observed. 

Under i-polarization light, the optical spectra of 5-nm nanoparticles (Fig. 7A), recorded at various incident angles 0 do not change with increasing 0. They are characterized by a maximum centered at 2.9 cV, which is similar to that observed for isolated particles (Fig. 5B). Flowever, the plasmon resonance peak remains asymmetrical, as observed under nonpolarized light (Fig. 6). 

The appearance of a plasmon resonance is strictly related to a distinct size of the corresponding metal, based on the presence of a confined electron gas that interacts with light and so results in typical colours. Is there also a minimum size where plasmon resonance is no longer possible In any case this must happen if a particle reaches a typical molecular status. There are no longer freely mobile... 

From these examples we may conclude that, as was indicated above, the question of having or not having a quantum confinement in a distinct particle allows different answers. All we may notice in this case is that gold, silver or copper particles of a distinct size must possess confined electron gases, but nanoparticles being too small to show a plasmon resonance cannot be excluded as having no confined electrons. On the contrary, as will be shown later by means of the Auss cluster. 

The presence of metallic surfaces or particles in the vicinity of a fluorophore can dramatically alter the fluorescence emission and absorption properties of the fluorophore. The effect, which is associated with the surface plasmon resonance of the metallic surface, depends on parameters such as metal type, particle size, fluorophore type and fluorophore-particle separation. 

In order to investigate this effect, ordered arrays of metallic nano-islands were fabricated on glass substrates by a process of natural lithography using monodisperse polystyrene nanospheres. The metal particle dimensions were tailored in order to tune the plasmon resonance wavelength to match the spectral absorption of the fluorophore. The fluorophore, Cy5 dye, which is widely used in optical immunoassays and has a medium quantum efficiency ( 0.3), was used in this preliminary study of the plasmonic enhancement effect. 

L.A. Lyon, D.J. Pena, and M.J. Natan, Surface plasmon resonance of Au colloid-modified Au films particle size dependence. J. Phys. Chem. B 103, 5826-5831 (1999). 

A clear, commonly accepted terminology to describe few-atom subnanoscale metals exhibiting quantized energy levels is lacking. The lack of a coherent terminology leads to confusion and may hamper development. In this chapter, we restrict the term metal cluster to describe few-atom metals with discrete energy levels, and use metal nanoparticle, for particles that have surface plasmon resonance effects (approximate size range between 1 and 100 nm). 

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