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Review
. 2019 Dec 27;5(1):41-48.
doi: 10.1021/acsomega.9b03560. eCollection 2020 Jan 14.

Aggregation of Metal-Nanoparticle-Induced Fluorescence Enhancement and Its Application in Sensing

Shuang Li  1   2 , Jiangling He  3   2 , Qing-Hua Xu  3   2
Affiliations
Review

Aggregation of Metal-Nanoparticle-Induced Fluorescence Enhancement and Its Application in Sensing

Shuang Li et al. ACS Omega. .

Abstract

Fluorescence-based detection methods have been widely utilized in various applications. Materials that display aggregation-induced emission (AIE) are excellent fluorescence probes to offer high contrast ratio. Chromophore-conjugated plasmonic metal nanoparticles (NPs) have been recently found to display significantly enhanced fluorescence emission upon the formation of aggregates. This new type of AIE enhancement has a totally different working mechanism. It is based on aggregation-induced plasmon coupling of metal NPs to enhance the fluorescence intensity of chromophores by increasing both the excitation efficiency and radiative decay rates, instead of reducing nonradiative decay rates as in typical AIE. AIE enhancement of chromophore-conjugated metal NPs results in a dramatic change in fluorescence intensity from severely quenched fluorescence to significantly enhanced fluorescence upon aggregate formation. It offers excellent contrast ratio and is attractive for developing platforms for highly sensitive sensing and imaging applications with reduced background. This mini-review summarizes the basic working principle and recent progress in fluorescence enhancement by coupled metal NPs on the single-molecule level, aggregation-induced plasmon coupling enhanced fluorescence of chromophore-conjugated metal NPs, and their applications in sensing. Perspectives on further utilization of this interesting phenomenon for various biomedical applications have also been discussed.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
(a) Schematic illustration of localized surface plasmon resonance of metal NPs. (b) Normalized extinction spectra of nanospheres (A), nanocubes (B), and nanorods with different aspect ratios (C–E), respectively. Electric fields of silver nanosphere monomer (c) and dimer (d). Reprinted with kind permission from refs (6) and (10). Copyright 2007 by Annual Reviews, 2008 American Chemical Society.
Figure 2
Figure 2
Working principle of metal-enhanced fluorescence. (a,b) Effects of metal–chromophore interactions on excitation and radiative and nonradiative decay processes of chromophores and (c) separation distance dependent metal-enhanced fluorescence. γEX, γEX′ are excitation rates in the absence and presence of plasmonic metal NPs.
Figure 3
Figure 3
(a) Finite-difference time-domain calculation of local electric field enhancement in the Au nanobowtie and (b) fluorescence enhancement of single dye molecules in the Au nanobowtie. Scale bar: 100 nm. Reprinted with kind permission from ref (20). Copyright 2009 American Chemical Society.
Figure 4
Figure 4
(a–c) Plasmon coupling enhanced fluorescence as a function of gap distance by using the Au nanorod dimer using the DNA origami method, and the average length of Au NRs is 43.5 nm. (d–f) Schematic illustration of fluorescence enhancement by the Au nanosphere dimer and trimer. (f) Fluorescence enhancement vs hot spot volume. Reprinted with kind permission from refs (21) and (22). Copyright 2015 American Chemical Society.
Figure 5
Figure 5
(a) Schematic illustration of optical antenna consisting of two 80 nm Ag or Au NPs attached to a DNA origami; (b–d) experimental fluorescence enhancement (b), simulated electric-field enhancement (c), and relative change in quantum yield (d) for different dyes by Ag (gray) or Au (yellow) NP dimers. Reprinted with kind permission from ref (24). Copyright 2017 American Chemical Society.
Figure 6
Figure 6
(a) Scheme of lighting up Au NPs quenched fluorescence by using Ag NPs; (b) fluorescence spectra of Au-RiTC NPs upon gradual addition of Ag@SiO2; and (c) optimum emission enhancements by SiO2-coated Ag NPs with different SiO2 shell thicknesses. Reproduced from ref (3) with permission. Copyright 2016 The Royal Society of Chemistry.
Figure 7
Figure 7
(a) Schematic illustration of coupled plasmonic structures. (b, c) Fluorescence enhancement of Cy5-Au NPs by different nanostructures (b) and Au@Ag NSs with two different diameters (c). (d) Improved scheme to place more Cy5 in the gap region. (e) Separation distance dependent fluorescence enhancement by 65 nm Au@Ag NSs. (f, g) Fluorescence enhancement factor with various concentrations of fully complementary target DNA (f) and 1 nM target DNA containing mismatched bases (g). Reprinted with kind permission from ref (4). Copyright 2018 American Chemical Society.
Figure 8
Figure 8
(a) Scheme of aggregation-induced plasmon coupling enhanced fluorescence of prequenched fluorophores. (b) Emission intensity of coupled Au@Ag-RiTC NPs (red), free RiTC (green), and isolated Au@Ag-RiTC NPs (black). (c) Fluorescence enhancement factors of coupled Au@Ag-RiTC vs isolated Au@Ag-RiTC (black) and free RiTC (green). (d) Emission spectra of Au@Ag(5.6 nm)-RiTC NPs upon addition of various amounts of cysteine. (e) Enhancement factors of coupled Au@Ag-RiTC NPs with various amino acids (10 μM) in tap water. Reproduced with permission from ref (5). 2019 The Royal Society of Chemistry.
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