Metallic nanoparticles metal-enhanced fluorescence

Cade NI, Ritman-Meer T, Kwaka K, Richards D (2009) The plasmonic engineering of metal nanoparticles for enhanced fluorescence and Raman scattering. Nanotechnology 20 285201... 

Aslan K, Wu M, Lakowicz JR, Geddes CD (2007) Fluorescent core-shell Ag Si02 nanocomposites for metal-enhanced fluorescence and single nanoparticle sensing platforms. J Am Chem Soc 129 1524-1525... 

In about 2000, my laboratory started to study the interactions of fluorophores with metallic nanoparticles, both solution-based and surface-immobilized. Our findings agreed with other workers whom had observed increases in fluorescence emission coupled with a decrease in the fluorophores radiative lifetime. Subsequently, we applied classical far-field fluorescence descriptions to these experimental observations, which ultimately suggested a modification in the fluorophores s intrinsic radiative decay rate, a rate thought to be mostly unchanged and only weakly dependent on external environmental factors. This simple description, coupled with what seemed like a limitless amount of applications led to a paper published by our laboratory in 2001 entitled Metal-Enhanced Fluorescence , or MEF, a term now widely used today almost a decade later. 

K. Aslan, P. Holley, and C. D. Geddes. Metal-enhanced fluorescence from silver nanoparticle-deposited polycarbonate substrates Journal of Materials Chemistry, 2006, 16, 2846-2852. 

Johansson, P., Xu, H., and Kail, M. (2005). Surface-enhanced Raman scattering and fluorescence near metal nanoparticles. Phys. Rev. B 72 035427-1-17. 

What emerges from the rigorous theoretical treatment in the previous section is that the Plasmon / metal interface plays several roles in the enhancement. Thus the measured fluorescence intensity in the presence of plasmon supporting metal nanoparticle is modified to ... 

Importance of Spectral Overlap Fluorescence Enhancement by Single Metal Nanoparticles... 

To understand the importance of spectral overlap to metal-enhanced fluorescence, it is useful to review the basics of metal-enhanced fluorescence. Metal nanostructures can alter the apparent fluorescence from nearby fluorophores in two ways. First, metal nanoparticles can enhance the excitation rate of the nearby fluorophore, as the excitation rate is proportional to the electric field intensity that is increased by the local-field enhancement. Fluorophores in such "hot spots" absorb more light than in the absence of the metal nanoparticle. Second, metal nanoparticles can alter the radiative decay rate and nonradiative decay rate of the nearby fluorophore, thus changing both quantum yield and the lifetime of the emitting species. We can summarize the various effects of a nanoparticle on the apparent fluorescence intensity, Y p, of a nearby fluorophore as ... 

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. 

Sabanayagam, C.R. and Lakowicz, J.R. (2007) Increasing the sensitivity of DNA microarrays by metal-enhanced fluorescence using surface-boimd silver nanoparticles. Nucleic Acids Res 35 el3. 

The detected fluorescence can be significantly enhanced, however, by exploiting the plasmonic enhancement which can occur when a metal nanoparticle (NP) is placed in the vicinity of a fluorescent label or dye [1-3]. This effect is due to the localised surface plasmon resonance (LSPR) associated with the metal NP, which modifies the intensity of the electromagnetic (EM) field around the dye and which, under certain conditions, increases the emitted fluorescence signal. The effect is dependent on a number of parameters such as metal type, NP size and shape, NP-fluorophore separation and fluorophore quantum efficiency. There are two principal enhancement mechanisms an increase in the excitation rate of the fluorophore and an increase in the fluorophore quantum efficiency. The first effect occurs because the excitation rate is directly proportional to the square of the electric field amplitude, and the maximum enhancement occurs when the LSPR wavelength, coincides with the peak of the fluorophore absorption band [4, 5]. The second effect involves an increase in the quantum efficiency and is maximised when the coincides with the peak of the fluorophore emission band [6]. 

Figure 7.1 (A) Sdiematic representation of the Metal-Enhanced Fluorescence phenomena (B) FDTD calculations for two silver nanoparticle arrays...

Fluorescence and Enhanced Local Field of Metallic Nanoparticles... 

Aslan, K., Wu, M., Lakowicz, J. R., Geddes, C. D. (2007). Fluorescent Core-Shell Ag Si02 Nanocomposites for Metal-Enhanced Fluorescence and Single Nanoparticle Sensing Platforms. J. Am. Chem. Soc. 129 1524-1525. 

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