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Far-field range fluorescence enhancement by a hybrid metal-dielectric structure

DONG Lin-xiu CHEN Zhi-hui YANG Yi-biao FEI Hong-ming LIU Xin

董林秀, 陈智辉, 杨毅彪, 费宏明, 刘欣. 金属-电介质复合结构实现荧光远场增强[J]. 中国光学, 2020, 13(2): 372-380. doi: 10.3788/CO.20201302.0372
引用本文: 董林秀, 陈智辉, 杨毅彪, 费宏明, 刘欣. 金属-电介质复合结构实现荧光远场增强[J]. 中国光学, 2020, 13(2): 372-380. doi: 10.3788/CO.20201302.0372
DONG Lin-xiu, CHEN Zhi-hui, YANG Yi-biao, FEI Hong-ming, LIU Xin. Far-field range fluorescence enhancement by a hybrid metal-dielectric structure[J]. Chinese Optics, 2020, 13(2): 372-380. doi: 10.3788/CO.20201302.0372
Citation: DONG Lin-xiu, CHEN Zhi-hui, YANG Yi-biao, FEI Hong-ming, LIU Xin. Far-field range fluorescence enhancement by a hybrid metal-dielectric structure[J]. Chinese Optics, 2020, 13(2): 372-380. doi: 10.3788/CO.20201302.0372

金属-电介质复合结构实现荧光远场增强

doi: 10.3788/CO.20201302.0372
基金项目: 

国家自然科学基金资助项目 11674239

国家自然科学基金资助项目 61575139

国家自然科学基金资助项目 61575138

详细信息
  • 中图分类号: O436.1

Far-field range fluorescence enhancement by a hybrid metal-dielectric structure

Funds: 

the National Natural Science Foundation of China 11674239

the National Natural Science Foundation of China 61575139

the National Natural Science Foundation of China 61575138

More Information
    Author Bio:

    Lin-xiu Dong(1992—), Master Degree Candidate, Key Lab of Advanced Transducers and Intelligent Control System, Ministry of Education and Shanxi Province, College of Physics and Optoelectronics, Taiyuan University of Technology.Her research interests are on micro/nano-photonics.E-mail:1355175076@qq.com

    Zhi-hui Chen(1984—), PhD, professor, Key Lab of Advanced Transducers and Intelligent Control System, Ministry of Education and Shanxi Province, College of Physics and Optoelectronics, Taiyuan University of Technology.His research interests are on micro/nano-photonics.E-mail:huixu@126.com

    Corresponding author: Zhi-hui Chen, E-mail:huixu@126.com
  • 摘要: 本文提出一种大尺度的金属-电介质复合微纳结构(银-硅结构),用于提高荧光生物检测的灵敏度及解决荧光物质距离结构远场范围时荧光增强的近场局限。这种大尺度的金属-电介质复合微纳结构与之前的金属-电介质复合微纳结构不同,其通过光的散射和干涉实现了荧光物质距离结构远场范围时的荧光增强。在本文中,通过采用时域有限差分法,主要从荧光激发和荧光发射两个过程研究银-硅结构。结果表明,在激发过程中,银-硅结构的荧光强度高于玻璃结构且位于银-硅结构两柱之间的狭缝中的电场分布比金属结构(银结构)更均匀,因此在银-硅结构中可以实现荧光增强,而且分子运动行为的检测更准确。在发射过程中,当荧光纳米粒子距离结构远场范围内时,与玻璃相比,银-硅结构可以实现更好的荧光增强效果。利用银-硅结构实现荧光增强的机理是光的散射和干涉,荧光被银膜向上散射,同时,结构两侧的银/硅柱也散射一部分荧光,荧光相互干涉传播至远场实现荧光增强。此外,银-硅结构易于制备和集成。因此,其可以很好地应用于生物传感领域。
  • Figure  1.  Schematic illustration of five structures. (a)Bare glass structure; (b)Si structure; (c)Ag structure; (d) Si-Ag structure; (e)Ag-Si structure

    Figure  2.  (a) Total fluorescence intensity of all six structures(the five structures in Fig. 1 and a silver film structure); (b) total electric field distributions of the five structures; (c) far-field angular distributions for the five structures at a wavelength of 610 nm; the QD 0.5 μm away from the Ag film and 1.0 μm away from the pillars

    Figure  3.  (a) The different polarizations for the Ag-Si structure; (b) the electric field distributions of the Ag-Si structure atdifferent polarizations at a wavelength of 610 nm; the QD is 0.5 μm away from the Ag film and 1.0 μm away from the pillars.

    Figure  4.  The fluorescence intensity of QD in the Ag-Si structure with different slit widths; the QD is 0.5 μm away from the Ag film and 1.0 μm away from the pillars.

    Figure  5.  The fluorescence intensity of the QD in the structure with different Ag/Si heights; QD is 0.5 μm away from the Ag film and 1.0 μm away from the pillars.

    Figure  6.  The intensity of the QD in different positions in the slit

    Figure  7.  (a) The fluorescence intensity of the QD in the Ag-Si structure with different slit widths at the central wavelength; (b)the fluorescence intensity of the QD in the structure with different Ag/Si heights at the central wavelength; (c)the intensity of the QD in different positions within the slit at the central wavelength; one point is marked by a circle to indicate the fluorescence intensity of the QD in a bare glass structure

    Figure  8.  The electric field distributions of Ag, Ag-Si, Si-Ag, SiO2 structures in the excitation process; the wavelength is 380 nm.

  • [1] 李红博, 尹坤.基于量子点的荧光型太阳能聚光器[J].中国光学, 2018, 10(5):555-567. doi:  10.3788/CO.20171005.0555

    LI H B, YIN K. Quantum dots based luminescent solar concentrator[J]. Chinese Optics, 2018, 10(5):555-567. (in Chinese) doi:  10.3788/CO.20171005.0555
    [2] 安娜, 卢睿, 马昊玥, 等. CdSe/CdS核壳量子点复合材料合成及其在白光发光二极管中的应用[J].发光学报, 2017, 38(8):1003-1009. http://www.wanfangdata.com.cn/details/detail.do?_type=perio&id=fgxb201708003

    AN N, LU R, MA H Y, et al.. Synthesis of CdSe/CdS core/shell quantum dots luminescent microspheres and their application for WLEDs[J]. Chinese Journal of Luminescence, 2017, 38(8):1003-1009. (in Chinese) http://www.wanfangdata.com.cn/details/detail.do?_type=perio&id=fgxb201708003
    [3] GUZATOV D V, VASCHENKO S V, STANKEVICH V V, et al..Plasmonic enhancement of molecular fluorescence near silver nanoparticles:theory, modeling, and experiment[J]. The Journal of Physical Chemistry C, 2012, 116(19):10723-10733. doi:  10.1021/jp301598w
    [4] TOBIAS AK, JONES M. Metal-enhanced fluorescence from quantum dot-coupled gold nanoparticles[J]. The Journal of Physical Chemistry C, 2019, 123(2):1389-1397. doi:  10.1021/acs.jpcc.8b09108
    [5] HOANG T B, AKSELROD G M, ARGYROPOULOS C, et al..Ultrafast spontaneous emission source using plasmonic nanoantennas[J]. Nature Communications, 2015, 6:7788. doi:  10.1038/ncomms8788
    [6] SHEN H M, LU G W, ZHANG T Y, et al..Molecule fluorescence modified by a slit-based nanoantenna with dual gratings[J]. Journal of the Optical Society of America B, 2013, 30(9):2420-2426. doi:  10.1364/JOSAB.30.002420
    [7] ZHANG J, FU Y, CHOWDHURY M H, et al..Metal-enhanced single-molecule fluorescence on silver particle monomer and dimer:coupling effect between metal particles[J]. Nano Letters, 2007, 7(7):2101-2107. doi:  10.1021/nl071084d
    [8] JIANG Y, WANG H Y, WANG H, et al..Surface plasmon enhanced fluorescence of dye molecules on metal grating films[J]. The Journal of Physical Chemistry C, 2011, 115(25):12636-12642. doi:  10.1021/jp203530e
    [9] KINKHABWALA A, YU Z F, FAN SH H, et al..Large single-molecule fluorescence enhancements produced by a bowtie nanoantenna[J]. Nature Photonics, 2009, 3(11):654-657. doi:  10.1038/nphoton.2009.187
    [10] LU G W, XU J N, WEN T, et al..Hybrid metal-dielectric nano-aperture antenna for surface enhanced fluorescence[J]. Materials, 2018, 11(8):1435. doi:  10.3390/ma11081435
    [11] NGO Q M, HO Y L D, PUGH J R, et al..Enhanced UV/blue fluorescent sensing using metal-dielectric-metal aperture nanoantenna arrays[J]. Current Applied Physics, 2018, 18(7):793-798. doi:  10.1016/j.cap.2018.04.007
    [12] RAY K, BADUGU R, SZMACINSKI H, et al..Several hundred-fold enhanced fluorescence from single fluorophores assembled on silver nanoparticle-dielectric-metal substrate[J]. Chemical Communications, 2015, 51(81):15023-15026. doi:  10.1039/C5CC03581C
    [13] SUN S, LI R, LI M, et al..Hybrid mushroom nanoantenna for fluorescence enhancement by matching the stokes shift of the emitter[J]. The Journal of Physical Chemistry C, 2018, 122(26):14771-14780. doi:  10.1021/acs.jpcc.8b01978
    [14] LAKOWICZ J R, RAY K, CHOWDHURY M, et al..Plasmon-controlled fluorescence:a new paradigm in fluorescence spectroscopy[J]. Analyst, 2008, 133(10):1308-1346. doi:  10.1039/b802918k
    [15] SUN S, LI M, DU Q G, et al..Metal-dielectric hybrid dimer nanoantenna:coupling between surface plasmons and dielectric resonances for fluorescence enhancement[J]. The Journal of Physical Chemistry C, 2017, 121(23):12871-12884. doi:  10.1021/acs.jpcc.7b02593
    [16] DUTTA CHOUDHURY S, BADUGU R, NOWACZYK K, et al..Tuning fluorescence direction with plasmonic metal-dielectric-metal substrates[J]. The Journal of Physical Chemistry Letters, 2013, 4(1):227-232. http://www.wanfangdata.com.cn/details/detail.do?_type=perio&id=333918e662e61172f12c612b8037afdb
    [17] BADUGU R, SZMACINSKI H, RAY K, et al..Metal-dielectric waveguides for high-efficiency coupled emission[J]. ACS Photonics, 2015, 2(7):810-815. doi:  10.1021/acsphotonics.5b00219
    [18] BOLIN F P, PREUSS L E, TAYLOR R C, et al..Refractive index of some mammalian tissues using a fiber optic cladding method[J]. Applied Optics, 1989, 28(12):2297-2303. doi:  10.1364/AO.28.002297
    [19] CHOWDHURY M H, RAY K, GRAY S K, et al..Aluminum nanoparticles as substrates for metal-enhanced fluorescence in the ultraviolet for the label-free detection of biomolecules[J]. Analytical Chemistry, 2009, 81(4):1397-1403. doi:  10.1021/ac802118s
    [20] CHEN ZH H, LIANG L, WANG Y, et al..Spatial remote luminescence enhancement by a half-cylindrical Au groove[J]. Journal of Materials Chemistry C, 2016, 4(47):11321-11327. doi:  10.1039/C6TC04074H
    [21] CHEN ZH H, SHI H, WANG Y, et al..Sharp convex gold grooves for fluorescence enhancement in micro/nano fluidic biosensing[J]. Journal of Materials Chemistry B, 2017, 5(44):8839-8844. doi:  10.1039/C7TB02422C
    [22] LIU F F, YU Y, LIN B X, et al..Visualization of hormone binding proteins in vivo based on Mn-doped CdTeQDs[J]. SpectrochimicaActa Part A:Molecular and Biomolecular Spectroscopy, 2014, 131:9-16. doi:  10.1016/j.saa.2014.04.066
    [23] WRENGER J P. Numerical reflection from FDTD-PMLs:a comparison of the split PML with the unsplit and CFS PMLs[J]. IEEE Transactions on Antennas and Propagation, 2002, 50(3):258-265. doi:  10.1109/8.999615
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  • 收稿日期:  2019-05-10
  • 修回日期:  2019-05-17
  • 刊出日期:  2020-04-01

Far-field range fluorescence enhancement by a hybrid metal-dielectric structure

doi: 10.3788/CO.20201302.0372
    基金项目:

    国家自然科学基金资助项目 11674239

    国家自然科学基金资助项目 61575139

    国家自然科学基金资助项目 61575138

    通讯作者: Zhi-hui Chen, E-mail:huixu@126.com
  • 中图分类号: O436.1

摘要: 本文提出一种大尺度的金属-电介质复合微纳结构(银-硅结构),用于提高荧光生物检测的灵敏度及解决荧光物质距离结构远场范围时荧光增强的近场局限。这种大尺度的金属-电介质复合微纳结构与之前的金属-电介质复合微纳结构不同,其通过光的散射和干涉实现了荧光物质距离结构远场范围时的荧光增强。在本文中,通过采用时域有限差分法,主要从荧光激发和荧光发射两个过程研究银-硅结构。结果表明,在激发过程中,银-硅结构的荧光强度高于玻璃结构且位于银-硅结构两柱之间的狭缝中的电场分布比金属结构(银结构)更均匀,因此在银-硅结构中可以实现荧光增强,而且分子运动行为的检测更准确。在发射过程中,当荧光纳米粒子距离结构远场范围内时,与玻璃相比,银-硅结构可以实现更好的荧光增强效果。利用银-硅结构实现荧光增强的机理是光的散射和干涉,荧光被银膜向上散射,同时,结构两侧的银/硅柱也散射一部分荧光,荧光相互干涉传播至远场实现荧光增强。此外,银-硅结构易于制备和集成。因此,其可以很好地应用于生物传感领域。

English Abstract

董林秀, 陈智辉, 杨毅彪, 费宏明, 刘欣. 金属-电介质复合结构实现荧光远场增强[J]. 中国光学, 2020, 13(2): 372-380. doi: 10.3788/CO.20201302.0372
引用本文: 董林秀, 陈智辉, 杨毅彪, 费宏明, 刘欣. 金属-电介质复合结构实现荧光远场增强[J]. 中国光学, 2020, 13(2): 372-380. doi: 10.3788/CO.20201302.0372
DONG Lin-xiu, CHEN Zhi-hui, YANG Yi-biao, FEI Hong-ming, LIU Xin. Far-field range fluorescence enhancement by a hybrid metal-dielectric structure[J]. Chinese Optics, 2020, 13(2): 372-380. doi: 10.3788/CO.20201302.0372
Citation: DONG Lin-xiu, CHEN Zhi-hui, YANG Yi-biao, FEI Hong-ming, LIU Xin. Far-field range fluorescence enhancement by a hybrid metal-dielectric structure[J]. Chinese Optics, 2020, 13(2): 372-380. doi: 10.3788/CO.20201302.0372
    • Fluorescence detection is widely used in many fields due to its simplicity of operation, high sensitivity and level of safety. However, the emission of a single fluorescent molecule is weak and difficult to capture. In order to improve the intensity of fluorescence of fluorescent substances(fluorescent dye, quantum dot[1-2], et al.), it is necessary to achieve fluorescence enhancement by using micro/nano structures.

      Metallic structures, including metal particles[3-4], metal nano-antenna[5] and metal gratings[6] can each be used to enhance fluorescence. For example, silver particle dimers with single Cy5 molecules have been proposed for enhancing fluorescence[7]. Significant fluorescence enhancement can be found when the Rhodamine 6G molecules are placed on Ag grating films[8]. Significant enhancement of a single molecule′s fluorescence on gold bowties has also been observed under appropriate conditions[9]. However, these metallic structures are limited by metal absorption, scattering loss and fluorescence quenching[10]. In contrast, the loss in the dielectric structure is less but the enhancement effect of fluorescence still needs further development. Taking full advantage of the large field enhancement of metal and the low loss characteristics of the dielectric, enhancing fluorescence with hybrid metal-dielectric structures[11] is also an option.For example, when the single Cy5 molecule is placed on the multilayer silver nanoparticle-dielectric-metal substrate, significant fluorescence enhancement is observed[12]. The hybrid mushroom nano antenna, which consists of a plasmonic metal stipe and a dielectric cap, is proposed to achieve fluorescence enhancement[13]. However, the shortcoming of these structures is that the fluorescent nanoparticle must be positioned less than one wavelength away from them. If the distance is too great, the effect of the fluorescence enhancement is significantly reduced. However, in tests, the fluorescent nanoparticle is often positioned more than one wavelength away from the structure. This demonstrates the necessity for studies of "far-field range" enhanced fluorescence.

      The Finite-Difference Time domain (FDTD) method is a numerical calculation of Maxwell′s equations in the time domain, which can provide the near-field and far-field properties for objects of any size or shape[14]. Thus, it is appropriate to study electromagnetism for micro/nano structures due to their accuracy and robustness.

      In this paper, a hybrid metal-dielectric structure is proposed to enhance fluorescence.The hybrid metal-dielectric(Ag-Si)structure is different from previous metal-dielectric structures. Firstly, it can achieve fluorescence enhancement when the fluorescent nanoparticle is in the far-field range away from the structure. Secondly, the mechanism of the fluorescence enhancement for previous metal-dielectric structures are metal plasmons resonance modes, coupling between surface plasmons, dielectric resonance modes[15] and microcavity modes[16], waveguide coupled emission modes[17], etc.A hybrid metal-dielectric(Ag-Si) structure can achieve fluorescence enhancement due to scattering and interference. The fluorescence of a Quantum Dot(QD) is scattered upward because of the silver film. Simultaneously, the silver and silicon pillars on both sides of the structure also scatter the partial fluorescence, then the fluorescence interferes and propagates to the far field to achieve far-field fluorescence enhancement. Using the FDTD method, the result shows that the fluorescence intensity of an Ag-Si structure is higher than that of the bare glass structure and that the electric field distribution of an Ag-Si structure is more uniform in the slit between the two pillars than it is for a metal structure in the excitation process. Furthermore, compared with bare glass, an Ag-Si structure can achieve fluorescence enhancement when the fluorescent nanoparticle is in the far-field range away from the structure during emission. The effects of the parameters of the Ag-Si structure on the fluorescence will also be discussed in this paper.

    • Fig. 1(a~d)(Color online) shows the structures with bare glass, silicon pillars, silver pillars, and silicon-silver pillars, respectively. The hybrid metal-dielectric structure (with silver-silicon pillars) is shown in Fig. 1 (e) wherein the silicon pillar is placed above the silver pillar, both pillars have a height of 500 nm (hAg=500 nm, hSi=500 nm, hS=1 μm) and the width of the slit between the two pillars is 2 μm (w=2 μm). The hybrid Ag-Si pillars are placed on a silver film covered glass substrate. The height of the silver film is 200 nm. A solution with a refractive index of 1.33[18] is filled into the slit.

      Figure 1.  Schematic illustration of five structures. (a)Bare glass structure; (b)Si structure; (c)Ag structure; (d) Si-Ag structure; (e)Ag-Si structure

      When the 3D structure is long enough in the z-direction, it can be simplified into a 2D model. The results of the 2D model is approximately the same as that of the 3D structure, meaning that its results could be extended to 3D geometry in real cases.These structures that are shown in Fig. 1 (a~e) are studied using the 2D FDTD method[19-21]. In the emission process, a dipole with a wavelength of 595 nm to 625 nm (with a central wavelength of 610 nm) which acts as a CdTeMn QD[22]is placed in the structures.A Perfect Match Layer Boundary Conditions(PML BC)was used as the absorbing boundary condition, which was used to absorb outgoing waves with negligible reflection[23].In order to avoid the reflection of the boundary conditions and their effects on fluorescence, the boundary conditions in both x and y directions are PMLs.The length of the power line monitor is 6 μm and the position of the power line monitor is at y=5 μm when the QD is fixed at (x, y)=(0, 0.5)μm. The power line monitor is 4.5 μm away from the dipole so the distance between them is much larger than one wavelength. This shows that the far-field fluorescence emission intensity can be estimated by the power monitor. In the excitation process, the boundary conditions in the x and y directions are Bloch and PML, respectively. For a plane wave, a PML BC in the x-direction will cause light truncation and lead to deviation in results.

      Bloch boundary conditions apply to periodic structures. The Bloch boundary is placed at least ten wavelengths away from the structure so that the interaction between the structures is negligible. A plane wave illuminates from above the structure and the excitation wavelength is 380 nm.

    • The total fluorescence intensity and total electric fields of the three polarizations(x, y, z-oriented) for the five structures are showed in Fig. 2 (a~b)(Color online), respectively. When the QD is 0.5 μm away from the silver film and 1.0 μm away from the pillars, the total fluorescence enhancement factor of the Ag-Si structure is higher compared with that of a bare glass and Si-Ag structure at the central wavelength. Additionally, the fluorescence intensity of the five structures in Fig. 1 are compared to a silver film structure. The fluorescence intensity of the Ag-Si structure is larger than it is for the silver film structure. Their diagrams are shown in Fig. 2(a).The total electric field distributions of the five structures can show the electric intensity intuitively in Fig. 2(b). A relatively strong field in the Ag-Si structure can be found compared to other structures due to scattering and interference.The far-field angular distributions for the five structures are shown in Fig. 2(c)(Color online) for the z-oriented polarization. The far-field directional emission of the Ag-Si structure is significantly stronger than that of other structures. The Ag-Si structure can achieve far-field directional fluorescence enhancement due to scattering and interference. The fluorescence of a QD is scattered upward by the silver film while the silver and silicon pillars on both sides of the structure also scatter the partial fluorescence, then the fluorescence interferes and propagates to the far field to achieve far-field directional fluorescence enhancement. The far-field directional fluorescence enhancement is conducive to the collection of fluorescence and improves detection sensitivity. This shows that the Ag-Si structure can be well applied in biosensing.However, the effect of fluorescence enhancement is related to polarization, the parameters of the Ag-Si structure and the position of the fluorescent nanoparticle.Each of these factors is discussed in the following paragraphs.

      Figure 2.  (a) Total fluorescence intensity of all six structures(the five structures in Fig. 1 and a silver film structure); (b) total electric field distributions of the five structures; (c) far-field angular distributions for the five structures at a wavelength of 610 nm; the QD 0.5 μm away from the Ag film and 1.0 μm away from the pillars

    • The fluorescence intensity of the different polarizations of the structures is shown in Fig. 3(a)(Color online). The fluorescence intensity of the z-oriented polarization is the strongest compared to that of the other polarization. The fluorescence intensity of the y-oriented polarization is the weakest. Fig. 3 (b)(Color online) shows the electric field distribution of the Ag-Si structure. The electric field distribution and the fluorescence intensity of emissions at different polarizations are consistent. So the z-oriented polarization of the QD is chosen mainly because its fluorescence intensity is greatly affected when the polarization of the QD is z-oriented.

      Figure 3.  (a) The different polarizations for the Ag-Si structure; (b) the electric field distributions of the Ag-Si structure atdifferent polarizations at a wavelength of 610 nm; the QD is 0.5 μm away from the Ag film and 1.0 μm away from the pillars.

    • Different slit widths in the structure may affect the intensity of light scattering and interference.The intensity of far-field fluorescence might also change. Therefore, determining the appropriate slit width will be of benefit to far-field fluorescence enhancement. The far-field fluorescence intensity of the QD in the Ag-Si structure with a slit width of 0.6, 0.8, 1.0, 1.2, 1.6, 2.0, 3.0 μm are each calculated. The fluorescence intensity of the QD in the Ag-Si structure with different slit widths is shown in Fig. 4. When the slit width is too narrow, more light is trapped inside the slit, which weakens the far-field fluorescence enhancement. However, when the slit is too wide, the effect of the structure will also weaken. When the slit is 2-μm wide, the intensity is higher than it is for other silt sizes at the central wavelength.

      Figure 4.  The fluorescence intensity of QD in the Ag-Si structure with different slit widths; the QD is 0.5 μm away from the Ag film and 1.0 μm away from the pillars.

    • The fluorescence intensity of a QD in the structure with different heights of the Ag/Si pillars is showed in Fig. 5. In one case, the height of the Ag pillars is fixed at 0.5 μm and the heights of Si pillar range from 0.3 to 2.0 μm. In the other case, the height of the Si pillar is fixed at 0.5 μm and the heights of the Ag pillar range from 0.3 to 2.0 μm. When the heights of the Si pillar and Ag pillar are both 0.5 μm, the power intensity of the QD has a distinct peak at the central wavelength, and the effect of fluorescence enhancement is more significant than at other heights. For this reason, the heights of the Ag and Si pillars are both chosen to be 0.5 μm in the following study.

      Figure 5.  The fluorescence intensity of the QD in the structure with different Ag/Si heights; QD is 0.5 μm away from the Ag film and 1.0 μm away from the pillars.

    • When the QD is randomly positioned within the slit at (x, y)=(0, 0.3), (0, 0.5), (0, 0.6), (0, 0.8), (0.8, 0.3), (0.5, 0.6)μm, the fluorescence intensity of the QD is calculated. The fluorescence intensity of the QD in different positions is shown in Fig. 6(Color online). We can see that the QD position can affect the fluorescence intensity because a change in its position affects the intensity of interference. Despite this, the fluorescence is still enhanced in the Ag-Si structure compared to the bare glass (black line) structure.Such advantages are fantastic for real biological detection.

      Figure 6.  The intensity of the QD in different positions in the slit

      In the discussion above, the fluorescence intensity is related to the slit width, height of the structu- res and QD′s position. To illustrate the results, the fluorescence intensity at different slit widths, heights and QD positions at the central wavelength are showed in Fig. 7(a~c). In Fig. 7(b), one point is marked by a circle to indicate the fluorescence intensity of the QD in a bare glass structure (hAg=0, hSi=0, hS=1 μm); the other points indicate the fluorescence intensity of the QD in the structure with different Ag/Si heights (the value (a, b) in the x-axis shows (hAg, hSi)) at the central wavelength; In Fig. 7(c), one point is marked by a circle to indicate the fluorescence intensity of the QD in the bare glass structure; the other points indicate the fluorescence intensity at different positions when the heights of the silver and silicon pillar both are 0.5 μm.It can be seen from Fig. 7(a~b) that the fluorescence intensity is better when the slit is 2 μm and the heights of the Ag and Si pillars both are 0.5 μm.

      Figure 7.  (a) The fluorescence intensity of the QD in the Ag-Si structure with different slit widths at the central wavelength; (b)the fluorescence intensity of the QD in the structure with different Ag/Si heights at the central wavelength; (c)the intensity of the QD in different positions within the slit at the central wavelength; one point is marked by a circle to indicate the fluorescence intensity of the QD in a bare glass structure

    • When the incident wavelength is 380 nm, the electric field distributions of the Ag structure and hybrid metal-dielectric structure are calculated during excitation. The electric field distributions are shown in Fig. 8(Color online).The fluorescence intensity of the Ag-Si structure is higher than the bare glass structure and the electric field distribution of the Ag-Si structure is more uniform in the slit between the two pillars than it is in Ag and Si-Ag structures. Therefore, fluorescence enhancement can be achieved and the detection of molecular motion behavior is more accurate in an Ag-Si structure.

      Figure 8.  The electric field distributions of Ag, Ag-Si, Si-Ag, SiO2 structures in the excitation process; the wavelength is 380 nm.

    • In this paper, a hybrid metal-dielectric structure is studied in the QD emission process and the excitation process. In the excitation process, the fluorescence intensity of the Ag-Si structure is higher than it is in the bare glass structure and the electric field distribution of the Ag-Si structure is more uniform in the slit between the two pillars than it is in the Ag and Si-Ag structures. In the emission process, the Ag-Si structure can achieve greater fluorescence enhancement. This paper provides an Ag-Si structure that can be applied in the field biosensing and provides a way of hybridizing the metal and dielectric components in micrometer scales.

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