Silver nanoparticles, surface plasmon effects

Gold nanoparticles are virtually not luminescent, but silver nanoparticles show plasmon emissions with reasonable quantum yields. Furthermore, the non-radiative decay, resulting in electron-hole pair generation, may be used for photosensitization of wide bandgap semiconductors (see Figure 7.5) [16,17]. Similar effects may also be observed as direct photoinduced electron transfer between metal surfaces and surface-bound molecules [18]. 

There are three major components of the MAMEF technique 1) plasmonic nanoparticles (i.e., silver, gold, copper, nickel, aluminum, zinc, etc.), 2) microwaves and 3) an aqueous assay medium. TTie plasmonic nanoparticles serve as (i) a platform for the attachment of one of the biorecognition partners (anchor probes) (ii) as an enhancer of the close-proximity fluorescence signatures via surface plasmons (i.e., MEF effect) [2] and (iii) a material not heated by microwaves for the selective heating of the aqueous media with microwave energy. 

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]. 

Malinsky MD, Kelly KL, Schatz GC, Van Duyne RP (2001) Nanosphere lithography effect of substrate on the localized surface plasmon resonance spectrum of silver nanoparticles. J Phys Oiem B 105 2343... 

The enhancement of surface plasmon absorption of metal nanoparticles may be a result of strong near-field coupling in the close-packed copper-silver nanostructure. The effect is more considerable at the spectral range outside of the copper interband absorption that is why it is not evident at the LSPA band of silver nanoparticles. At th e fi equency range near the LSPA band of copper nanoparticles, near-field coupling is not suppressed by die interband absorption so much and the LSPA enhancement is well seen. 

High enhancement of the copper localized surface plasmon absorbency was recorded at the two-layer planar system consisted of copper and silver nanoparticles prepared with successive vacuum evaporation. The result obtained may be caused by strong near-field coupling in the close-packed binary system. The effect may be used for the development of high-absorptive coatings and spectral selective nanoelements in the visible and near infrared spectral ranges. 

To study particle correlation effects in the plasmon resonance absorption in the visible we have firstly compared the spectral characteristics of silver nanoparticles monolayers at the various particle surface concentrations o (Fig- ) The monolayer overlap parameter j = ngn d l4 was equal to 0.4 for the particle diameter of... 

Figure 16.4 Effect of gold-silver alloy formation on the surface plasmon absorption. Part (a) shows the UV/Vis absorption spectra of spherical gold-silver alloy nanoparticles of varying composition. The gold mole fraction Xau varies between 1.0 and 0.27. The dependence of the maximum of the plasmon absorption as a function of the nanoparticle composition and the particle diameter are given in (b) and (c), respectively. (Reproduced with permission from S. Link and M. El-Sayed, 1999 J. Phys. Chem. B 103 8410-8426. Copyright 1999 American Chemical Society.)...

Fig. 5.3-16 Effect of formation of a gold-silver alloy on the surface plasmon absorption measured UV-VIS absorption spectra of spherical Au—Ag alloy nanoparticles of various compositions. The gold mole fraction xau varies between 1 and 0.27. The plasmon absorption maximum is blueshifted with decreasing Xau- (After [3.74])...

The absorption peaks at about 400 nm due to the surface plasmon resonance effect could be seen to be blue-shifted with the decrease in size of silver nanoparticles (inset of Figure 4). The blue-shift is attributed to contraction of... 

In the present review, we describe the effects of different silver nanostructures that were prepared by various methods in our laboratories on the emission intensity of fluorophores with various quantum yields and on biochemical fluorophores. The silver nanostructures consist of subwavelength size nanoparticles of silver deposited on inert substrates. These particles display a surface plasmon absorption, which in the small... 

In recent years we have been reporting our observations on the favorable effects of silver nanoparticles deposited randomly on glass substrates (silver island films) for increasing the intensities and photostability of fluorophores, particularly those with low quantum yields. These reports described fluorophores with visible excitation and emission wavelengths. Since the fluorophores interact with metal through die surface plasmon resonance, for-silver the absorption maximum is near 430 nm, we did not know if silver particles would enhance the emission of ICG with absorption and emission... 

Surface plasmon resonance is due to the absorption of light at the srtrface of a metal, typically gold or silver. The effect extends only up to a few Inmdred nanometers into the material. At the surface, the electrons around the metal nuclei behave as a plasma and can be excited by light that couples with the frequency of their collective oscillation (resonance). Due to the confinement of the electrons by the physical dimensions of the nanoparticle, the excitation energy increases as the particle size decreases. A similar effect was described earher for excitons in semiconductor nanoparticles. 

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