Spherical metallic nanoparticles

Scattering of Evanescent Waves by Spherical Metallic Nanoparticles... 

Nitzan and Brus fust suggested the possibility of siuface plasmon enhanced photochemistry in 1981 [13, 14]. They studied a phenomenological model for a molecule interacting with a small spherical metal nanoparticle that can support a SP resonance when irradiated. The model was derived in detail in a subsequent paper by Gersten and Nitzan [15]. I will thus refer to the model as the Nitzan-Brus-Gerstan or NBG model. The calculations based on the NBG model showed that both UV photodissociation and IR multiphoton absorption could be surface plasmon enhanced [13, 14]. 

Many experiments have been carried out where the distance between the fluorophore and the metal nanoparticle surface is varied yet only quenching is observed. In these cases the nanoparticles are usually small spherical metal nanoparticles. The following examples demonstrate distance-dependent quenching in a couple of nanoparticle-fluorophore systems. 

Me]x-MCM-41 containing nanosized particles of platinum, palladium, rhodium, ruthenium and iridium were directly synthesised from surfactant stabilised spherical metal nanoparticles in the synthesis gel, and characterised with XRD, ICP-AES, TG/DSC, TEM, nitrogen physisorption and carbonmonoxide chemisorption, and Si MAS NMR. During the synthesis some agglomeration of the particles took place, but the metal particles were present inside the pore system of MCM-41. The matericils were active and selective catalysts in the hydrogenation of cyclic olefins such as cyclohexene, cyclooctene, cyclododecene and norbomene. 

As mentioned above. Ere/ (and thus Emoz) can be highly amplified when the incident field has a frequency in resonance with a plasmon excitation. For metal nanoparticle small with respect to the wavelength, only the dipolar plasmon can be excited. It is educative to recall (see Sec. 1.4.1) the very simple case (a small spherical metal nanoparticle described by the Drude dielectric constant in the vacuum) and compare its absorption spectrum (dominated by the plasmon band) and the intensity of Ere/ at a fixed point along the direction of oscillation of the dipolar plasmon. The absorption cross-section Cabs is given by (see Eq. (1.299)) ... 

There is an enormous market available for sensors or devices that can measure or simply detect some highly diluted chemical analyte. Detection of hormones, DNA, or toxins at the level of a few molecules at a time has significant value. This is reflected in the great number of papers and patents in this area. Here we will survey the more popular schemes. Spherical metallic nanoparticles, generally as a proof of concept, have demonstrated remarkable utility as substrates for these applications [114-116] however, gold nanorods and nanoshells could be even better [117-119] due to their more tunable optical properties. 

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