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Whispering-gallery nanocavity plasmon-enhanced Raman spectroscopy.

Zhang J, Li J, Tang S, Fang Y, Wang J, Huang G, Liu R, Zheng L, Cui X, Mei Y - Sci Rep (2015)

Bottom Line: The synergy effect in nature could enable fantastic improvement of functional properties and associated effects.The detection performance of surface-enhanced Raman scattering (SERS) can be highly strengthened under the cooperation with other factors.Such synchronous and coherent coupling between plasmonics and photonics could lead to new principle and design for various sub-wavelength optical devices, e.g. plasmonic waveguides and hyperbolic metamaterials.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials Science, Fudan University, Shanghai 200433, People's Republic of China.

ABSTRACT
The synergy effect in nature could enable fantastic improvement of functional properties and associated effects. The detection performance of surface-enhanced Raman scattering (SERS) can be highly strengthened under the cooperation with other factors. Here, greatly-enhanced SERS detection is realized based on rolled-up tubular nano-resonators decorated with silver nanoparticles. The synergy effect between whispering-gallery-mode (WGM) and surface plasmon leads to an extra enhancement at the order of 10(5) compared to non-resonant flat SERS substrates, which can be well tuned by altering the diameter of micron- and nanotubes and the excitation laser wavelengths. Such synchronous and coherent coupling between plasmonics and photonics could lead to new principle and design for various sub-wavelength optical devices, e.g. plasmonic waveguides and hyperbolic metamaterials.

No MeSH data available.


Related in: MedlinePlus

Raman enhancement in a whispering-gallery plasmon nanocavity.(a,b) SEM image (a) and Raman intensity mapping (b) of the R6G signal at 1364 cm−1 on a rolled-up plasmon nanocavity. The original R6G concentration is 10−5 M and the excitation wavelength is 514.5 nm. (c) Raman spectra of the line scan along the green arrow marked in a. The blue stars refer to the intensity of 1650 cm−1 band extracted from the spectra. (d) A comparison of SERS detection limits on Ag NP-decorated plasmon nanocavities (I), undecorated nanotubes (II) and flat silver-NP-decorated nanomembrane (III). The concentrations of R6G solution used are marked in the figure.
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f2: Raman enhancement in a whispering-gallery plasmon nanocavity.(a,b) SEM image (a) and Raman intensity mapping (b) of the R6G signal at 1364 cm−1 on a rolled-up plasmon nanocavity. The original R6G concentration is 10−5 M and the excitation wavelength is 514.5 nm. (c) Raman spectra of the line scan along the green arrow marked in a. The blue stars refer to the intensity of 1650 cm−1 band extracted from the spectra. (d) A comparison of SERS detection limits on Ag NP-decorated plasmon nanocavities (I), undecorated nanotubes (II) and flat silver-NP-decorated nanomembrane (III). The concentrations of R6G solution used are marked in the figure.

Mentions: To evaluate the Raman enhancement capacity and the sensitivity of the device, we test the device in different imaging configurations. A rolled-up tubular plasmon cavity with a diameter of 850 nm is fabricated and imaged by SEM (Fig. 2a). Three regions with different morphologies, including Ag NPs array on SiO/TiO2 nanomembrane (in the left side of plamsmon nanocavity), tubular plamsmon nanocavity and silicon substrate (in the right side of plamsmon nanocavity), are clearly shown. Rhodamine solution (R6G, 10−5 M), which was used as a probe chemical here, was subsequently dropped into the device area and dried in air for the Raman measurement. A 514.5-nm laser was used to excite the Raman spectra of R6G, and a 2D micro-Raman mapping corresponding to an area of 3.2 × 1.8 μm2 was acquired. The color-coded Raman mapping in Fig. 2b shows the peak intensity at 1364 cm−1 of R6G in different positions. It is observed that the three areas (dark red, bright yellow and dark black from the left to the right) of the Raman intensity map exactly correlates with three regions of the sample in the SEM (Fig. 2a), which indicates an extra enhancement of Raman intensity for R6G on the nanocavity. Detailed Raman spectra at different featured locations along the green arrow in Fig. 2a are displayed in Fig. 2c. On the bare silicon substrate, no Raman signal can be detected, while Raman spectra of R6G are obtained on the 2D NP array. It indicates that surface plasmon modes in silver nanoparticles are excited and contribute to the enhancement of Raman scattering (i.e. SERS). As for the spectra from plasmonic tubular nanocavity, the SERS effect is remarkably enhanced, as shown in the red spectra of Fig. 2c. Such SERS enhancement on plasmon nanocavity suggests that besides surface plasmon effect of silver nanoparticles, the tubular geometry which supports WGMs could greatly improve SERS due to a coupling effect. We then quantitatively explore the magnitude of Raman enhancement in the tubular nanocavities. A series of R6G solutions with various concentrations from 10−1 to 10−13 M were prepared and measured on three different kinds of substrates. The lowest detectable concentration for R6G solution on each substrate and the corresponding Raman spectra are revealed in Fig. 2d. For the NP-decorated plasmonic nanocavities, the detection limit can be as low as 10−12 M (spectra I in Fig. 2d). Interestingly, rolled-up TiO2/SiO nanocavities without silver NPs (spectra II in Fig. 2d) also provide an enhanced Raman detection limit (down to 10−7 M R6G solution) compared to flat nanomembranes without silver nanoparticles (spectra III in Fig. 2d). Our calculation shows that the EF of Raman signal in plasmonic nanocavities approach the order of 1010. (See detailed results and calculations in Supplementary Notes, Part 2)


Whispering-gallery nanocavity plasmon-enhanced Raman spectroscopy.

Zhang J, Li J, Tang S, Fang Y, Wang J, Huang G, Liu R, Zheng L, Cui X, Mei Y - Sci Rep (2015)

Raman enhancement in a whispering-gallery plasmon nanocavity.(a,b) SEM image (a) and Raman intensity mapping (b) of the R6G signal at 1364 cm−1 on a rolled-up plasmon nanocavity. The original R6G concentration is 10−5 M and the excitation wavelength is 514.5 nm. (c) Raman spectra of the line scan along the green arrow marked in a. The blue stars refer to the intensity of 1650 cm−1 band extracted from the spectra. (d) A comparison of SERS detection limits on Ag NP-decorated plasmon nanocavities (I), undecorated nanotubes (II) and flat silver-NP-decorated nanomembrane (III). The concentrations of R6G solution used are marked in the figure.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4595732&req=5

f2: Raman enhancement in a whispering-gallery plasmon nanocavity.(a,b) SEM image (a) and Raman intensity mapping (b) of the R6G signal at 1364 cm−1 on a rolled-up plasmon nanocavity. The original R6G concentration is 10−5 M and the excitation wavelength is 514.5 nm. (c) Raman spectra of the line scan along the green arrow marked in a. The blue stars refer to the intensity of 1650 cm−1 band extracted from the spectra. (d) A comparison of SERS detection limits on Ag NP-decorated plasmon nanocavities (I), undecorated nanotubes (II) and flat silver-NP-decorated nanomembrane (III). The concentrations of R6G solution used are marked in the figure.
Mentions: To evaluate the Raman enhancement capacity and the sensitivity of the device, we test the device in different imaging configurations. A rolled-up tubular plasmon cavity with a diameter of 850 nm is fabricated and imaged by SEM (Fig. 2a). Three regions with different morphologies, including Ag NPs array on SiO/TiO2 nanomembrane (in the left side of plamsmon nanocavity), tubular plamsmon nanocavity and silicon substrate (in the right side of plamsmon nanocavity), are clearly shown. Rhodamine solution (R6G, 10−5 M), which was used as a probe chemical here, was subsequently dropped into the device area and dried in air for the Raman measurement. A 514.5-nm laser was used to excite the Raman spectra of R6G, and a 2D micro-Raman mapping corresponding to an area of 3.2 × 1.8 μm2 was acquired. The color-coded Raman mapping in Fig. 2b shows the peak intensity at 1364 cm−1 of R6G in different positions. It is observed that the three areas (dark red, bright yellow and dark black from the left to the right) of the Raman intensity map exactly correlates with three regions of the sample in the SEM (Fig. 2a), which indicates an extra enhancement of Raman intensity for R6G on the nanocavity. Detailed Raman spectra at different featured locations along the green arrow in Fig. 2a are displayed in Fig. 2c. On the bare silicon substrate, no Raman signal can be detected, while Raman spectra of R6G are obtained on the 2D NP array. It indicates that surface plasmon modes in silver nanoparticles are excited and contribute to the enhancement of Raman scattering (i.e. SERS). As for the spectra from plasmonic tubular nanocavity, the SERS effect is remarkably enhanced, as shown in the red spectra of Fig. 2c. Such SERS enhancement on plasmon nanocavity suggests that besides surface plasmon effect of silver nanoparticles, the tubular geometry which supports WGMs could greatly improve SERS due to a coupling effect. We then quantitatively explore the magnitude of Raman enhancement in the tubular nanocavities. A series of R6G solutions with various concentrations from 10−1 to 10−13 M were prepared and measured on three different kinds of substrates. The lowest detectable concentration for R6G solution on each substrate and the corresponding Raman spectra are revealed in Fig. 2d. For the NP-decorated plasmonic nanocavities, the detection limit can be as low as 10−12 M (spectra I in Fig. 2d). Interestingly, rolled-up TiO2/SiO nanocavities without silver NPs (spectra II in Fig. 2d) also provide an enhanced Raman detection limit (down to 10−7 M R6G solution) compared to flat nanomembranes without silver nanoparticles (spectra III in Fig. 2d). Our calculation shows that the EF of Raman signal in plasmonic nanocavities approach the order of 1010. (See detailed results and calculations in Supplementary Notes, Part 2)

Bottom Line: The synergy effect in nature could enable fantastic improvement of functional properties and associated effects.The detection performance of surface-enhanced Raman scattering (SERS) can be highly strengthened under the cooperation with other factors.Such synchronous and coherent coupling between plasmonics and photonics could lead to new principle and design for various sub-wavelength optical devices, e.g. plasmonic waveguides and hyperbolic metamaterials.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials Science, Fudan University, Shanghai 200433, People's Republic of China.

ABSTRACT
The synergy effect in nature could enable fantastic improvement of functional properties and associated effects. The detection performance of surface-enhanced Raman scattering (SERS) can be highly strengthened under the cooperation with other factors. Here, greatly-enhanced SERS detection is realized based on rolled-up tubular nano-resonators decorated with silver nanoparticles. The synergy effect between whispering-gallery-mode (WGM) and surface plasmon leads to an extra enhancement at the order of 10(5) compared to non-resonant flat SERS substrates, which can be well tuned by altering the diameter of micron- and nanotubes and the excitation laser wavelengths. Such synchronous and coherent coupling between plasmonics and photonics could lead to new principle and design for various sub-wavelength optical devices, e.g. plasmonic waveguides and hyperbolic metamaterials.

No MeSH data available.


Related in: MedlinePlus