Abstract
In the present work we study the surface-enhanced resonant Raman scattering (SERRS) and fluorescence (SEF) spectra of a general model molecule confined in metallic dimers consisting of Ag, Au and hybrid AuAg nanoparticles (NPs). The electromagnetic (EM) enhancement factors were simulated by the generalized Mie scatting method and the scattering cross section of the molecules were obtained by density-matrix calculations. The influence of the size of the NPs and the separation between the dimer on the Raman scattering and fluorescence were systematically studied and analyzed in detail. It was found that the SERRS mainly related to EM enhancement and the SEF depended on the competition between EM enhancement and quantum yield, both of which could be controlled by tuning the radius and separation of the metallic dimers. The optimal radius of the NPs for SERRS were found to be around 30 nm for AgNPs, 40 nm for AuNPs and 50 nm for hybrid AuAgNPs. The strongest Raman enhancement as predicted by the theoretical simulations were 6.2 × 1010, 1.5 × 107 and 5.2 × 108 for the three types of structures, respectively. These results could offer valuable information for the design of metallic substrates for surface enhanced Raman and fluorescence measurements.
Highlights
With the development of single-molecule detective technology, surface-enhanced resonant Raman scattering (SERRS) has become a valuable tool for surface science, medical diagnostics and biomedical applications due to the ultrahigh sensitivity and stability[1,2,3,4,5]
We use the density-matrix approach developed by Xu et al to calculate the surface-enhanced Raman scattering and fluorescence of a Rhodamine 6 G (R6G) molecule confined in metallic dimers
We can find that a decrease of d causes a clear red-shift to the resonance peaks caused by the localized surface plasmon resonance (LSPR)
Summary
With the development of single-molecule detective technology, surface-enhanced resonant Raman scattering (SERRS) has become a valuable tool for surface science, medical diagnostics and biomedical applications due to the ultrahigh sensitivity and stability[1,2,3,4,5]. The Raman cross section of a molecule near metallic nanoparticles (NPs) will be enhanced by the fourth power of the EM enhanced factor M13,14. For the metallic dimer configuration, the EM enhancement (M) and scattering cross section are related to many factors, such as the material of the substrate, the size of the NPs, the separation between NPs, as well as the laser photon energy. All of these factors have to be considered in the actual design of active substrate which could become quite complicated in the experiment. By comparing the scattering spectra of AgNPs, AuNPs and hybrid AuAgNPs with different radius and separation, the optimal configurations of the three substrates were presented for improving the accuracy and sensitivity in actual testing
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