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Plasmon-induced broadband fluorescence enhancement on Al-Ag bimetallic substrates.

Hao Q, Du D, Wang C, Li W, Huang H, Li J, Qiu T, Chu PK - Sci Rep (2014)

Bottom Line: While the detection sensitivity of SEF is improved with the development of nano-techniques, detection of multiple analytes by SEF is still a challenge due to the compromise between the high enhancing efficiency and broad response bandwidth.Fluorescence from different dyes excited by 310 nm to 555 nm is enhanced by up to 11 folds on the single bimetallic film and the result is theoretically confirmed by finite-difference time-domain simulations.This work demonstrates that bimetallic film can be used for optical detection of multiple analytes.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Physics, Southeast University, Nanjing 211189, P. R. China [2] Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, P. R. China.

ABSTRACT
Surface enhanced fluorescence (SEF) utilizes the local electromagnetic environment to enhance fluorescence from the analyte on the surface of a solid substrate with nanostructures. While the detection sensitivity of SEF is improved with the development of nano-techniques, detection of multiple analytes by SEF is still a challenge due to the compromise between the high enhancing efficiency and broad response bandwidth. In this article, a high-efficiency SEF substrate with broad response bandwidth is obtained by embedding silver in an aluminum film to produce additional bonding and anti-bonding hybridized states. The bimetallic film is fabricated by ion implantation and the ion energy and fluence are tailored to control subsurface location of the fabricated bimetallic nanostructures. The process circumvents the inherent limit of aluminum materials and extends the plasmon band of aluminum from deep UV to visible range. Fluorescence from different dyes excited by 310 nm to 555 nm is enhanced by up to 11 folds on the single bimetallic film and the result is theoretically confirmed by finite-difference time-domain simulations. This work demonstrates that bimetallic film can be used for optical detection of multiple analytes.

No MeSH data available.


Normalized fluorescence emission spectra acquired from the bimetallic film (upper) and quartz (lower).The bimetallic films are prepared by silver implantation (20 kV, 5 × 1016 cm−2). The dashed line shows the extinction spectrum of the bimetallic film and the excitation wavelengths for different fluorescence molecules are shown. The number on top of each curve shows the peak wavelength of the fluorescence emission spectrum. The enhancement factors are about 10, 3, 11, and 4 for 2-AP, 7-HC, AF555, and RB molecules.
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f1: Normalized fluorescence emission spectra acquired from the bimetallic film (upper) and quartz (lower).The bimetallic films are prepared by silver implantation (20 kV, 5 × 1016 cm−2). The dashed line shows the extinction spectrum of the bimetallic film and the excitation wavelengths for different fluorescence molecules are shown. The number on top of each curve shows the peak wavelength of the fluorescence emission spectrum. The enhancement factors are about 10, 3, 11, and 4 for 2-AP, 7-HC, AF555, and RB molecules.

Mentions: Fluorescence enhancement is observed from the bimetallic films as shown in Fig. 1. Four different fluorescent molecules including 2-AP, 7-HC, AF 555 and RB with quantum yields of 0.6831, 0.7632, 0.1 and 0.3133 in solution are used (molecular formulas shown in Fig. S1). The scaled fluorescence spectra are compared in Fig. 1 and fluorescence enhancement factors of ~10x, ~3x, ~11x, and ~4x are observed from 2-AP, 7-HC, AF 555, and RB, respectively. The photoluminescence efficiency can be attributed to two major factors: an enhanced local field and an increase of the intrinsic decay rate of the molecules. The first factor promotes plasmon resonance energy transfer from the bimetallic plasmonic structures to nearby fluorescent molecules34. The UV-Vis spectrum of the bimetallic film (dashed line) shows plasmon band from 200 to 600 nm representing the LSPR energy and the photoluminescence excitation spectrum peak (excitation wavelength) for different molecules are marked on the dashed line with colors. Similar to the donor-acceptor energy matching in fluorescent resonance energy transfer between two fluorophores, critical matching between the LSPR energy and excitation energy from the ground to excited states of the fluorescent molecules permits the plasmon resonance energy transfer process. The quantized energy is likely transferred via the dipole-dipole interaction between the resonating plasmon dipole in the plasmonic structures and molecules. Here, the bimetallic films act as the plasmonic antennae by converting a part of the nonradiative near-field emission of the fluorophore into far-field emission to create the observed emission35. However, coupling between the LSPR energy and fluorescence emitting energy decreases the efficiency because the emission signal has a probability to be absorbed again by the plasmonic material. This is consistent with our results that the enhancement factor of 2-AP is much higher (~10X) than the enhancement factor of 7-HC (~3X). Besides, the optical emission is also influenced by modification of the molecular radiative decay rate by the nearby metallic nanoparticle which results in increased quantum yields and decreased lifetime. Importantly, these effects are larger for fluorophores with lower quantum yields. If the dye has a high quantum yield close to 100%, then the additional radiative decay rate cannot substantially increase the quantum as the energy transfer quenching to the metal will dominate in this case36. It should be noted that the quantum field data shown in this paper are measured in solution and can only be used as reference index. This is because molecule quantum field has a high sensitivity to the microenvironment and may be different when molecule is absorbed on a solid film surface. In addition, our bimetallic films were coated with a 5 nm SiO2 layer before the fluorescence measurement in order to protect the films from oxidation and optimize the fluorescence emission. As we know, fluorescence from a molecule directly adsorbed onto the surface of a metallic nanoparticle is strongly quenched while at a distance of a few nanometers from the nanoparticles its fluorescence can be strongly enhanced37. In conclusion, our results suggest that the silver implanted aluminum bimetallic films are promising in applications requiring optical enhancement in the deep UV to visible range.


Plasmon-induced broadband fluorescence enhancement on Al-Ag bimetallic substrates.

Hao Q, Du D, Wang C, Li W, Huang H, Li J, Qiu T, Chu PK - Sci Rep (2014)

Normalized fluorescence emission spectra acquired from the bimetallic film (upper) and quartz (lower).The bimetallic films are prepared by silver implantation (20 kV, 5 × 1016 cm−2). The dashed line shows the extinction spectrum of the bimetallic film and the excitation wavelengths for different fluorescence molecules are shown. The number on top of each curve shows the peak wavelength of the fluorescence emission spectrum. The enhancement factors are about 10, 3, 11, and 4 for 2-AP, 7-HC, AF555, and RB molecules.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4127495&req=5

f1: Normalized fluorescence emission spectra acquired from the bimetallic film (upper) and quartz (lower).The bimetallic films are prepared by silver implantation (20 kV, 5 × 1016 cm−2). The dashed line shows the extinction spectrum of the bimetallic film and the excitation wavelengths for different fluorescence molecules are shown. The number on top of each curve shows the peak wavelength of the fluorescence emission spectrum. The enhancement factors are about 10, 3, 11, and 4 for 2-AP, 7-HC, AF555, and RB molecules.
Mentions: Fluorescence enhancement is observed from the bimetallic films as shown in Fig. 1. Four different fluorescent molecules including 2-AP, 7-HC, AF 555 and RB with quantum yields of 0.6831, 0.7632, 0.1 and 0.3133 in solution are used (molecular formulas shown in Fig. S1). The scaled fluorescence spectra are compared in Fig. 1 and fluorescence enhancement factors of ~10x, ~3x, ~11x, and ~4x are observed from 2-AP, 7-HC, AF 555, and RB, respectively. The photoluminescence efficiency can be attributed to two major factors: an enhanced local field and an increase of the intrinsic decay rate of the molecules. The first factor promotes plasmon resonance energy transfer from the bimetallic plasmonic structures to nearby fluorescent molecules34. The UV-Vis spectrum of the bimetallic film (dashed line) shows plasmon band from 200 to 600 nm representing the LSPR energy and the photoluminescence excitation spectrum peak (excitation wavelength) for different molecules are marked on the dashed line with colors. Similar to the donor-acceptor energy matching in fluorescent resonance energy transfer between two fluorophores, critical matching between the LSPR energy and excitation energy from the ground to excited states of the fluorescent molecules permits the plasmon resonance energy transfer process. The quantized energy is likely transferred via the dipole-dipole interaction between the resonating plasmon dipole in the plasmonic structures and molecules. Here, the bimetallic films act as the plasmonic antennae by converting a part of the nonradiative near-field emission of the fluorophore into far-field emission to create the observed emission35. However, coupling between the LSPR energy and fluorescence emitting energy decreases the efficiency because the emission signal has a probability to be absorbed again by the plasmonic material. This is consistent with our results that the enhancement factor of 2-AP is much higher (~10X) than the enhancement factor of 7-HC (~3X). Besides, the optical emission is also influenced by modification of the molecular radiative decay rate by the nearby metallic nanoparticle which results in increased quantum yields and decreased lifetime. Importantly, these effects are larger for fluorophores with lower quantum yields. If the dye has a high quantum yield close to 100%, then the additional radiative decay rate cannot substantially increase the quantum as the energy transfer quenching to the metal will dominate in this case36. It should be noted that the quantum field data shown in this paper are measured in solution and can only be used as reference index. This is because molecule quantum field has a high sensitivity to the microenvironment and may be different when molecule is absorbed on a solid film surface. In addition, our bimetallic films were coated with a 5 nm SiO2 layer before the fluorescence measurement in order to protect the films from oxidation and optimize the fluorescence emission. As we know, fluorescence from a molecule directly adsorbed onto the surface of a metallic nanoparticle is strongly quenched while at a distance of a few nanometers from the nanoparticles its fluorescence can be strongly enhanced37. In conclusion, our results suggest that the silver implanted aluminum bimetallic films are promising in applications requiring optical enhancement in the deep UV to visible range.

Bottom Line: While the detection sensitivity of SEF is improved with the development of nano-techniques, detection of multiple analytes by SEF is still a challenge due to the compromise between the high enhancing efficiency and broad response bandwidth.Fluorescence from different dyes excited by 310 nm to 555 nm is enhanced by up to 11 folds on the single bimetallic film and the result is theoretically confirmed by finite-difference time-domain simulations.This work demonstrates that bimetallic film can be used for optical detection of multiple analytes.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Physics, Southeast University, Nanjing 211189, P. R. China [2] Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, P. R. China.

ABSTRACT
Surface enhanced fluorescence (SEF) utilizes the local electromagnetic environment to enhance fluorescence from the analyte on the surface of a solid substrate with nanostructures. While the detection sensitivity of SEF is improved with the development of nano-techniques, detection of multiple analytes by SEF is still a challenge due to the compromise between the high enhancing efficiency and broad response bandwidth. In this article, a high-efficiency SEF substrate with broad response bandwidth is obtained by embedding silver in an aluminum film to produce additional bonding and anti-bonding hybridized states. The bimetallic film is fabricated by ion implantation and the ion energy and fluence are tailored to control subsurface location of the fabricated bimetallic nanostructures. The process circumvents the inherent limit of aluminum materials and extends the plasmon band of aluminum from deep UV to visible range. Fluorescence from different dyes excited by 310 nm to 555 nm is enhanced by up to 11 folds on the single bimetallic film and the result is theoretically confirmed by finite-difference time-domain simulations. This work demonstrates that bimetallic film can be used for optical detection of multiple analytes.

No MeSH data available.