Gold nanoparticles excitation enhancement

Figure 27 NIR luminescence from gold nanoparticles is enhanced if excitation occours via energy transfer from surface-bound fluorophores. (Reproduced with permission from Ref. 52. 2007, American Chemical Society.)...

The last problem of this series concerns femtosecond laser ablation from gold nanoparticles [87]. In this process, solid material transforms into a volatile phase initiated by rapid deposition of energy. This ablation is nonthermal in nature. Material ejection is induced by the enhancement of the electric field close to the curved nanoparticle surface. This ablation is achievable for laser excitation powers far below the onset of general catastrophic material deterioration, such as plasma formation or laser-induced explosive boiling. Anisotropy in the ablation pattern was observed. It coincides with a reduction of the surface barrier from water vaporization and particle melting. This effect limits any high-power manipulation of nanostructured surfaces such as surface-enhanced Raman measurements or plasmonics with femtosecond pulses. 

In summary, the photoluminescence of CdSe quantum dots can be strongly enhanced by nearby metal nanoparticles, where most of the enhancement results from excitation effects. We observed that the shape of the PLE spectra of the quantum dots near a metal nanoparticle is significantly altered for both gold and Ag nanoparticles, and shows a new PLE peak coincident with the LSPR peak of the metal nanoparticle. Although the absolute enhancement factor varies from one metal nanoparticle to another, the wavelength dep>endence of the total enhancement factor still mirrors the line shape of the metal nanoparticle s scattering spectrum. There may be a small offset in the maximum excitation enhancement from the nanoparticle s scattering peak (as was described for the total fluorescence in Section 4.3 above), but at present our experiments have not had sufficient spectral resolution to identify any such shift. 

The excitation of the surface plasmon effect also induces strongly enhanced fluorescence properties of gold nanoparticles due to the enhanconent in the radiative rate of the inter-band electronic transitions relative to that in bulk metals. Metal nanoparticles, especially gold nanorods exhibit enhanced two-photon luminescence (TPL) and multi-photon luminescoice (MPL) [7, 8]. Strongly-enhanced TPL has been observed from individual particles [9, 10] and particle solutions [11] under femtosecond NIR laser excitation. This observation raises the possibility of nonlinear optical imaging in the NIR region, where water and biomolecules have... 

Akiyama, T., M. Nakada, N. Terasaki, S. Yamada. (2006). Photocurrent enhancement in a porphyrin-gold nanoparticle nanostructure assisted by localized plasmon excitation. Chem. Commun. 395-397. 

Figure 4.17c shows a typical topography image of dimeric and isolated gold nanoparticles prepared on a cover slip. From the SEM observation of the sample, particles in the aggregate do not directly contact each other but are separated by a few nanometer to 10 nm. A two-photon excitation image of the sample is shown in Fig.4.17d. The image obtained sensitively reflects the optical field distribution of the sample. The optical field of the sample was greatly enhanced at the dimers (and at the trimer) in comparison with the isolated nanoparticles. Among four dimers in the sample, two dimers whose axes were parallel to the polarization of the incident light exhibited huge enhancements at the interstitial sites of the dimers. The other two dimers, whose axes are perpendicular to the incident field, showed only little...

Raman measurements with laser intensities of 10 W cm and accumulation times of 1 sec and less, and excitation with 830 nm (out of resonance) preclude from the observation of non-SERS spectra from the cells. However, at positions in the cells where gold nanoparticles are present, surface-enhanced Raman spectra can be measured in the living cells in their physiological environment. 

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...

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