Gold nanoparticles local field enhancement

Metal nanoparticles present localized surface plasmon resonances (LSPRs) that are collective excitations of the electrons at the interface between a conductor and a dielectric. The resonant plasma oscillation causes local field enhancement, and this is utilized in SERS [61,62], second-harmonic generation [63], and scanning near-field optical microscopy [64]. In particular, certain metals such as silver and gold have been much studied due to the feet that they present this LSPR in the visible spectral region. 

In coupled nanoparticle systems, the distance between the nanoparticles plays a key role in the enhancement of the local field and SERS enhancement factor. The smaller the gap size of a gold nanosphere dimer, the stronger the extinction intensity, and the larger the maximum SERS enhancement factor. It is worth noting that, for small gaps, the enhancement factors increase much more quickly than the increase of extinction coeflBcient. More importantly, when the gap is close to 1-2 nm the enhancement factor in the gap can reach up to 10 to 10 °, and facilitates single-molecule detection [65]. 

Figure 3, Basic concept of intracellular SERS probes Gold nanoparticles are transferred into cells. Aggregates which provide optimum SERS enhancement and are typically utilized in the live cell experiments are shown in the transmission electron micrograph and the schematic drawing. During excitation with laser light in the near-infrared (h VjJ, such gold nanoaggregates provide enhanced local optical fields in their nm-scaled vicinity, leading to surface-enhanced Stokes (h and anti Stokes...

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]. 

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