Abstract
Surface-enhanced resonance Raman scattering (SERRS) of rhodamine 6G was measured on confeito-like Au nanoparticles (CAuNPs). The large CAuNPs (100 nm in diameter) in aqueous dispersion systems showed stronger enhancing effect (analytical enhancement factor: over 105) of SERRS than the small CAuNPs (50 nm in diameter), while the spherical Au nanoparticles (20 nm in diameter) displayed rather weak intensities. Especially, minor bands in 1400–1600 cm−1 were uniquely enhanced by the resonance effect of CAuNPs. The enhancement factors revealed a concentration dependence of the enhancing effect at low concentration of rhodamine 6G. This dependency was due to a large capacity of hot-spots on CAuNPs, which were formed without agglomeration. The surface-enhancing behaviour in the film systems was similar to that in the dispersions, although the large CAuNPs had lower enhancing effect in the films, and the small CAuNPs and the spherical Au nanoparticles were more effective in their films. These results suggest that the CAuNPs have an advantage in ultrasensitive devices both in dispersions and films, compared to the agglomerate of spherical Au nanoparticles.
Highlights
Over the ages, nanoparticles of noble metals have been used as pigments [1]
These results suggest that the confeito-like Au nanoparticles (CAuNPs) have an advantage in ultrasensitive devices both in dispersions and films, compared to the agglomerate of spherical Au nanoparticles
The strong resonance between the excitation wavelength, surface plasmon, and molecular band allowed enhancing even the minor bands, which were not significantly enhanced by the spherical AuNPs. This difference suggested that the CAuNPs had hot-spots without agglomeration and enhanced the Raman scattering of R6G via the Surface-enhanced resonance Raman scattering (SERRS) mechanism
Summary
Nanoparticles of noble metals have been used as pigments [1]. They can efficiently absorb the light at a specific band, and their optical behavior is today understood as a resonance of collective motion of surface electrons with the incident light [1,2,3]. Surface-enhanced Raman scattering (SERS) [8,9,10], infrared absorption [11,12,13,14,15,16,17,18,19,20,21,22], and fluorescence spectroscopies [23,24,25] are used for ultrasensitive analyses To improve these enhancing effects, the LSPR can be tuned by designing the size and morphology of nanoparticles. This work will be useful to design the plasmonic devices for ultrahighly sensitive analyses
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