Surface plasma resonance

In this Section we want to present one of the fingerprints of noble-metal cluster formation, that is the development of a well-defined absorption band in the visible or near UV spectrum which is called the surface plasma resonance (SPR) absorption. SPR is typical of s-type metals like noble and alkali metals and it is due to a collective excitation of the delocalized conduction electrons confined within the cluster volume [15]. The theory developed by G. Mie in 1908 [22], for spherical non-interacting nanoparticles of radius R embedded in a non-absorbing medium with dielectric constant s i (i.e. with a refractive index n = Sm ) gives the extinction cross-section a(o),R) in the dipolar approximation as ... 

Nuclear component of the stopping power SPR Surface plasma resonance... 

The formation of Au nanoparticles can be easily monitored by following the appearance of a surface plasma resonance band around 520-540 nm (Fig. 6.1). Yeung et al. [33] observed that the efficiency of gold particle formation was different in different alcohols (n-pentanol > propan-2-ol > methanol). This is due to the air/water surface activity of the alcohols and the ability of the solute to scavenge the primary OH radicals at the bubble/liquid interface. 

One simple explanation for these results was as follows The electric field at a metal vacuum interface can be >10 times larger than in free space when the conditions required for a surface plasma resonance are met (47). Since the Raman cross-section is proportional to the square of the field, surface plasmons could produce enhancements of >10. This enhancement is probably not large enough to explain the tunneling junction results by itself, but an enhancement in signal of a factor of 100 by the excitation of surface plasmons would increase the Raman intensity from near the limits of detectibility. 

TRAP recruitment requires Hgand-induced changes in receptors that allow simultaneous interactions of each TRAP trimer with three receptor intracellular domains. This observation implicates that monomeric TRAF-receptor interactions are of low affinity so that the interactions do not occur in the absence of receptor activation. A number of quantitative biophysical characterizations with isothermal titration calorimetry (ITC) and surface plasma resonance (SPR) have provided solid support to this view (Table III). 

One further development of this approach has been to link chelating iminodiacetic acid groups to PEG, which in turn can be bound by Cu ions and so provide a highly specific binding site for Hisj-tagged proteins (Cha et al., 2004). Another variation is gold-coated microarrays, which have the advantage that they can be combined with surface plasma resonance (SPR) and MS for further detection and analysis of the captured molecules (Bieri et al., 1999 Houseman et... 

Chance B 1991 Optical method Annu. Rev. Biophys. Biophys. Chem. 20 1-28 Granstrom M, Berggren M and Ingan s O 1995 Micrometer- and nanometer-sized polymeric light-emitting diodes Science 267 1479-81 Hanken D G and Com R M 1995 Variable index of refraction ultrathin films formed from self-assembled zirconium phosphonate multilayers Characterization by surface plasma resonance measurements and polarization/modulation FT-IR spectroscopy Anal. Chem. 67 3761-74... 

In Rothberg s germinal work, they note the selective adsorption of ssDNA on AuNPs and show that ssDNA can stablize AuNPs against aggregation at a salt concentration that would ordinarily screen the repulsive interactions of citrate ions (Li and Rothberg, 2004). Because of that, the color of AuNPs is determined principally by surface plasma resonance, and because it is dramatically affected by nanoparticle aggregation, a simple colorimetric hybridization assay can be realized by using the difference between ssDNA and dsDNA electrostatic properties. 

B = C) and decreases with increasing eccentricity. Vice versa, following from equation (5), G2(e) also starts with GaCO) =4, but it increases with increasing eccentricity. It follows now from equation (4) that for a spheroidal silver particle, two surface plasma resonances are induced, namely, when the optical constants of silver satisfy the conditions... 

Fig. 7 Effect of pH on the surface plasma resonance absorbance on UV-vis spectra of Au-CAH/ CMC aqueous solution. Inset photos show the color of the Au-CAH/CMC dispersions at different pH (Reprinted, with permission, from [228], Copyright (2010) American Chemical Society)...

Both the nature of the ACP binding domain on ENR and other FAS components remains to be elucidated. Earlier studies from our laboratory have clearly shown that ENR will bind to ACP as will a number of other components of FAS. The use of cocrystallisation studies and surface plasma resonance spectroscopy should enable us to define which units interact and the nature of the important interactions. This will be fundamental in understanding the complete molecular architecture of FAS and possible limitations on its assembly in vivo. 

Gordon, J. and Swalen, J. (1977). The effect of thin organic films on the surface plasma resonance on gold. Opt. Common., 22 374 -376. 

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