Surface plasmons, nanostructured

When the size of metals is comparable or smaller than the electron mean free path, for example in metal nanoparticles, then the motion of electrons becomes limited by the size of the nanoparticle and interactions are expected to be mostly with the surface. This gives rise to surface plasmon resonance effects, in which the optical properties are determined by the collective oscillation of conduction electrons resulting from the interaction with light. Plasmonic metal nanoparticles and nanostructures are known to absorb light strongly, but they typically are not or only weakly luminescent [22-24]. 

Similar to zero-dimensional metal nanoparticles, most of the work on one-dimensional metal nanostructures focuses almost exclusively on gold nanorods. The high interest in anisometric gold nanoclusters arises from their unique optical and electronic properties that can be easily tuned through small changes in size, structure (e.g., the position, width, and intensity of the absorption band due to the longitudinal surface plasmon resonance is strongly influenced by the shell as well as the aspect ratio of the nanorods), shape (e.g., needle, round capped cylinder, or dog bone), and the inter-particle distance [157]. 

Reversible attachment of nanostructures at molecular printboards was exemplified by the adsorption and desorption of CD-functionalized nanoparticles onto and from stimuli-responsive pre-adsorbed ferrocenyl-dendrimers at a CD SAM (Fig. 13.7).65 Electrochemical oxidation of the ferrocenyl endgroups was employed to induce desorption of the nanostructure from the CD SAM. An in situ adsorption and desorption of ferrocenyl dendrimers and CD-functionalized Au nanoparticles (d 3 nm) onto and from the molecular printboard was observed by a combination of surface plasmon resonance spectroscopy (SPR) and electrochemistry. Similar behavior was observed when larger CD-functionalized silica nanoparticles (d 60 nm) were desorbed from the surface with the aid of ultrasonication. 

To understand the profound effect that nanostracturing can have on light, with the help of surface plasmons, we consider the simplest nanostructure a gap between two metals. 

Metal nanostructures (such as particles and apertures) can permit local resonances in the optical properties. These local resonances are referred to as localized surface plasmons (LSPs). The simplest version of the LSP resonance comes for a spherical nanoparticle, where the electromagnetic phase-retardation can be neglected in the quasi-static approximation, so that the electric field inside the particle is uniform and given by the usual electrostatic solution [3] ... 

Nanostructure-Based Localized Surface Plasmon Resonance Biosensors... 

Keywords Nanostructures Surface plasmon resonance Localized surface plasmon resonance Bio-molecular interactions Refractive index change Effective medium Thin films Biosensors Sensitivity Nanoparticles... 

Surface relief nanostructures may be used to create LSPs. In contrast to using particles to excite plasmons, surface relief patterns have an advantage of no aggregation and thus offer reliable sensing performance. Much part of the discussion addresses field enhancement in the near-field. Near-field enhancement can lead to amplification of signals produced by bio-molecular interactions near surface. 

Here, 1 examine the coupling of particle plasmons excited in nanoparticles with LSPs in surface relief nanostructures. As a biosensor, nanoparticles may serve as linker molecules that amplify the index change due to ligand bindings with... 

In the case of using a substrate with surface-relief nanostructures, overall trends would agree with what is mentioned in (Sect. 2.1.2), i.e., momentum-matching would occur at higher plasmon momentum. Since gold nanoparticles act as a target of supermolecules, plasmon momentum would be shifted further, which may induce nonlinear plasmon characteristics. Here, the effects of particle parameters, such as particle size, concentration, shape, and interaction distance between metal surface and nanoparticles, are discussed briefly based on experimental data of the interaction between particle plasmons and conventional SPs. 

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