Enhancing Fluorescence with Sub‐Wavelength Metallic Apertures

Blair, Steve; Wenger, Jérôme

doi:10.1002/9780470642795.ch17

Cited by 4 publications

(3 citation statements)

References 93 publications

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“…A fluorescent molecule can be treated as a system of three energy levels: a singlet ground state S 0 , a first excited singlet state S 1 , and a first excited triplet state T 1 . The fluorescence count rate per molecule (CRM) in steady state is given by , CRM = κ ϕ σ I e 1 + I e / I s where κ is the light collection efficiency (combination of the optical system and radiation profile), ϕ = k rad / k tot is the quantum yield (QY), k rad and k nr are the rate constants for radiative emission and nonradiative transition from S 1 to S 0 , k tot = k rad + k nr , the inverse of the excited state lifetime τ, σ I e is the net excitation rate, σ is the absorption cross-section, and the saturation intensity I s = k tot /[σ(1 + k isc / k d )], where k isc and k d are the rate constants for intersystem crossing to the triplet state and relaxation to the ground state, respectively. Based on eq , CRM modification by plasmonic structures consists of three contributions: local increase in the excitation intensity I e , local increase in the radiative emission k rad and QY ϕ of enclosed fluorophores, and modification of the collection efficiency κ.…”

Section: Simulationmentioning

confidence: 99%

UV Fluorescence Lifetime Modification by Aluminum Nanoapertures

et al. 2014

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We report excited-state lifetime modification of diffusing molecules by Al nanoapertures in the UV. Lifetime reductions of ∼3.5× have been observed for the high quantum yield laser dye p-terphenyl in a 60 nm diameter aperture. The lifetime reduction is smaller for the low quantum yield molecule tryptophan, for which a maximum reduction of ∼1.7 is observed. Lifetime reduction as a function of aperture size and native quantum yield is accurately predicted by simulation. Simulation further predicts greater net fluorescence enhancement for tryptophan compared to p-terphenyl, which is consistent with the expectation that low quantum yield emitters experience greater enhancement in the effective quantum yield. T here has been a recent surge of interest in UV plasmonics. 1−5 One of the motivating factors is accessing the electronic resonances of organic molecules, which lie in the UV part of the spectrum. Biomolecules such as peptides and proteins contain residues that absorb in the 220−280 nm range. 6,7 However, these aromatic residues have relatively low fluorescence quantum yields and molar extinction coefficients, 6,8 as do nucleic acids. 9 Achieving significant emission enhancement via plasmonic structures 10 could be a key enabling factor in the label-free detection of proteins 11 or DNA molecules. 12,13 Furthermore, there are numerous organic dye labels that absorb and fluoresce in the UV. 14 To date, there have been no reports of UV plasmonicenhanced fluorescence of freely diffusing molecules, nor has lifetime modification in the UV been reported. Arguably the most successful plasmonic nanostructure for analyzing freely diffusing molecules is the simple nanoaperture (of various shapes), which has been used extensively with visible fluorescence 15−20 as well as for the basis for novel label-free methods. 21,22 While several of these studies used Al nanoapertures, others adopted Au in order to realize greater fluorescence and local field enhancements in the visible. 23−25 However, conventional "plasmonic" metals such as Au suffer from the influence of interband transitions near the blue part of the spectrum. Therefore, studies to date of plasmonic structures in the UV have employed other metals, such as Al. 10,14,26−37 Aluminum has an interband transition near 800 nm with a Drude-like free-electron response from the visible to UV wavelengths. 38 Here, we use round Al nanoapertures to investigate UV fluorescence lifetime reduction of diffusing molecules, which is a first step toward more quantitative fluorescence analysis. We further show that the lifetime reduction depends on the native quantum yield of the molecule and is sensitive to the physical details of the nanoaperture, including undercutting of the nanoaperture into the substrate. ■ SIMULATION Fluorescence Model. A fluorescent molecule can be treated as a system of three energy levels: a singlet ground state S 0 , a first excited singlet state S 1 , and a first excited triplet state T 1 . The fluorescence count rate per molecule (CRM) in steady state is ...

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Section: Simulationmentioning

confidence: 99%

UV Fluorescence Lifetime Modification by Aluminum Nanoapertures

et al. 2014

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“…Modification of fluorescence dynamics is briefly described here. , The change in quantum yield can be expressed as where f rad = k rad ′ / k rad is the ratio of the radiative rate with the presence of metallic structure ( k rad ′ ) and without the structure ( k rad ).…”

Section: Computational Detailsmentioning

confidence: 99%

Magnesium as a Novel UV Plasmonic Material for Fluorescence Decay Rate Engineering in Free Solution

et al. 2017

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We report modification of the ultraviolet (UV) fluorescence decay rate of p-terphenyl dye molecules by magnesium (Mg) nanoapertures in free solution, in comparison with aluminum (Al). Mg nanoapertures exhibit a lifetime reduction of up to ∼7.2×, which to our knowledge is the largest lifetime reduction of a UV fluorescence dye reported so far in the literature. In comparison, Al nanoapertures exhibit a lifetime reduction of ∼5.3×, exceeding the previously reported value ∼3.5× due to smaller aperture size employed here. Simulation results reveal large plasmon resonance frequency shifts between Mg and Al nanoapertures, contributing to different lifetime reductions, where average lifetime reductions of Mg nanoapertures are greater than those of Al nanoapertures with diameters smaller than 40 nm. The dependence of count rate per molecule (CRM) on aperture size and aperture undercut is also reported, revealing that CRM increases with increasing undercut.

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“…8,9 One potential area of use for such metallic nanoaperture arrays is in microarray technologies. 10 The substrates generally used in a microarray platform contain an array of spots of immobilized probe oligonucleotides.…”

Section: Introductionmentioning

confidence: 99%

Enhanced fluorescence sensing with nano-apertures

et al. 2010

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We have been studying fluorescence enhancement from labeled oligonucleotides immobilized inside metallic nanoapertures. Fluorescence enhancement is a direct result of the localized field intensity enhancement within these nanoapertures from plasmonic excitation. We have also been developing specific surface chemistries for metallic films to localize capture oligos only inside these nanoapertures. Some of our recent results are overviewed.

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Enhancing Fluorescence with Sub‐Wavelength Metallic Apertures

Cited by 4 publications

References 93 publications

UV Fluorescence Lifetime Modification by Aluminum Nanoapertures

UV Fluorescence Lifetime Modification by Aluminum Nanoapertures

Magnesium as a Novel UV Plasmonic Material for Fluorescence Decay Rate Engineering in Free Solution

Enhanced fluorescence sensing with nano-apertures

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