【作者】 傅强；

【导师】 明海； 张斗国；

【作者基本信息】 中国科学技术大学 ， 光学， 2013， 博士

【摘要】 金属微纳结构的表面等离子体共振效应具有表面局域和近场增强的特点,正是由于这种金属所具有的独特的光学性质,使其在生化传感、表面增强拉曼散射(SERS)、增加非线性系数、金属增强荧光(MEF)等众多领域都有重要而广阔的应用。本论文以自制的多种不同形貌的金属微纳结构为前提,以研究金属微纳结构及其耦合体系的光学性质作为目的,重点从实验角度来研究其在光学传感、SERS及荧光成像等方面的应用。本论文的工作对于开发成本低廉、实时快速、免标签、灵敏度较高的光学传感器芯片和发展工艺简单、对比度高的荧光成像技术等方面具有重要的研究意义。本论文的主要研究内容和取得的成果如下：1.利用成本低廉、产率较大的化学方法制备了多种不同形貌的金属微纳结构,其中包括用种子辅助生长法制备的金纳米棒、金@银核-壳型双金属纳米棒,用多元醇还原法制备的银纳米立方体和银纳米线。利用光学刻蚀技术在负性光刻胶上刻写了周期可调的纳米光栅,并通过真空沉积镀膜技术制备了金属纳米光栅；2.从Gans理论出发,分析研究了金纳米棒以及金@银核-壳型双金属纳米棒的光学传感特点。实验中通过改变金纳米棒的长径比及其周围介质的折射率,发现金纳米棒的纵向局域表面等离子体共振峰(Lognitudinal Localized Surface Plasmon Resonance peak, LLSPR peak)将会随着长径比或者周围介质折射率的增大发生红移；通过制备技术在金纳米棒表面包覆了不同厚度的单质银纳米壳后,发现厚度对传感性能有明显影响,实验发现纳米银壳的包覆厚度为5nm时,折射率灵敏度和品质因子可以获得最佳平衡,其灵敏度达到321nm/RIU,品质因子可达4.0,后者要比未包覆前的金纳米棒提高74%；3.通过将化学法合成的银立方体与基于光刻技术制备的金属光栅复合构成双层SERS基底,通过研究拉曼散射强度的变化研究了这种双层结构中表面等离激元的相互耦合所带来的新颖的光学性质。实验结果表明,这种双层结构间的耦合可以大大提高SERS强度,对于拉曼探针分子罗丹明6G (Rh6G)在1650cm-1的振动峰,这种双层耦合结构比单纯的光栅结构的拉曼峰高提高了196倍,并且这种双层耦合结构也优于银立方体与平面银膜构成的双层结构,前者的峰高为35940a.u.,后者为2548a.u.,两者相差近14倍。最后我们从表面等离激元相互耦合的角度解释了这一实验结果；4.利用表面等离激元相互耦合的光学性质,我们还从实验角度开展了提高荧光成像对比度的研究。实验中将银纳米线／银纳米颗粒／聚苯乙烯小球、掺有荧光分子罗丹明B (RhB)的PMMA间隔层和平面银膜复合,组成“三明治”结构,通过CCD观察RhB荧光发射强度的变化进而影响荧光像明暗的方法来研究这种“三明治”结构的表面等离子体共振性质。实验结果表明,最上层和最下层的金属纳米结构之间的间距较小(50nm)的时候,会引起荧光的粹灭,而间距增大(110nm)时又会引起荧光的增强。在对金属结构的荧光成像中,无论是荧光的粹灭或者增强,都会提高成像的对比度。其中粹灭效应使荧光像对比度是明场像的2.25倍,增强效应使荧光像对比度是明场像的2倍。对于非金属介质聚苯乙烯小球来说,因为不存在表面等离激元的共振耦合,所以其荧光像对比度与明场相比没有明显变化。本论文的创新点主要包括：1.发现了包覆厚度对金@银核-壳型双金属纳米棒光学传感性能的影响。结果表明：对于长径比为3.0的金纳米棒,在其表面包覆5nm厚的银纳米壳后,其折射率灵敏度达到321nm/RIU,品质因子可达4.0,后者比未包覆前的金纳米棒提高74%；2.提出了银纳米立方体和银纳米光栅这样一种双层耦合结构,并从实验上发现这种双层耦合基底会大大提高SERS强度,其中比单层的一维银纳米光栅增强196倍,比银立方体和平面银膜构成的双层结构也要增强近14倍。这一实验结果对于开发结构简单、成本低廉、重复性好和高灵敏度的SERS传感、检测芯片具有较大的参考价值；3.提出了用金属-介质-金属的“三明治”结构来提高荧光成像的对比度,通过改变中间介质层的厚度,可以调控荧光的粹灭或者增强,同时发现无论是荧光被粹灭还是被增强,金属微纳结构荧光像的对比度都可以得到明显提高,其中粹灭效应使荧光像对比度是明场像的2.25倍,增强效应使荧光像对比度是明场像的2倍。更多还原

【Abstract】 The surface plasmon resonance of metallic nano-structures has two important characteristics:focalized electrical field and near-field enhancement. Because of these two unique optical characteristics owned by metal, there are significant and wide applications, such as biochemical sensor, surface enhanced Raman scattering (SERS), enhanced nonlinear optics, metal enhanced fluorescence (MEF), etc. This dissertation foucus on the optical properties of plasmonic coupling system made of metallic nano-structures of different morphology. We also investigated their appliciations in optical sensing, SERS and fluorescence imaging from an experimental viewpoint. Our work has potential significance to exploit low cost, real-time, free label and highly sensitive optical sensor chip and to develop simple-production, high-contrast fluorescence imaging technique.The main research works and conclusions are described as follows:1. We synthesized various metallic nano-structures of different shapes by the chemical method which is of low cost and large yield. These nano-structures included gold nanorods and god(?)@silver bimetallic nanorods which are synthesized by seed-mediated growth, silver nanocubes and silver nanowires synthesized by polyol reduction method. We also inscribed the sinusoidal metal grating by two beam interference and thermal evaporation technology;2. The optical properties of gold nanorods and gold@silver bimetallic nanorods are investigated based on Gans theory. In our experiment, we find that the lognitudinal localized surface plasmon resonance (LLSPR) peak of gold nanorods are red-shifted when the dielectric constant of surrounding medium or the aspect ratio of gold nanorods was increased. When silver nano-shell is coated on the surface of gold nanorods, we find that the optical sensing characteristics are significantly affected by thickness of silver nano-shell. When the thickness of silver nano-shell is5nm, the refractive index sensitivity (RIS) and the figure of merit (FOM) can achieve the best balance, and the RIS is321nm/RIU, the FOM is4.0, the latter is74%higher than that of uncoated gold nanorods;3. We experimentally investigated the novel optical properties of the chemically- synthesized silver nanocubes and lithography-inscribed metal grating by the surface enhanced Raman spectroscopy (SERS). The result shows that the intensity of SRES peak can be immensely enhanced by the dual-layer coupling structure. We compared the SERS intensity collected from the single-layer structure composed of only silver film or one dimensional silver grating or silver nanocubes. We find that the intensity of rhodamine6G (Rh6G) at1650cm-1collected from dual-layer is196times higher than that from single-layer substrate such as the silver grating. The SERS intensity of dual-layer substrate composed of silver nanocubes and silver grating is also larger than the dual-layer substrate composed of silver nanocubes and silver film. The former intensity is35940a.u and the latter is2548a.u.;4. We experimentally investigated the contrast enhancement of fluorescence image by the coupling of surface plasmons. We design the "sandwich" structure composed of silver nanocubes (or silver nanoparticles or plystyrene spheres), PMMA thin film which is doped with rhodamine B (RhB) and silver film We study the plasmonic characteristic of this "sandwich" structure by the fluorescence emission from the RhB. We find that when the thickness of PMMA film is50nm, the plasmonic coupling effect will give rise to the quench of fluorescence, but when the thickness of PMMA film is110nm, the plasmonic coupling effect will lead to the enhancement of fluorescence. Whether the fluorescence is quenched or enhanced, the contrast of fluorescence image of metallic nano-structure can be increased. For example, the quenching effect can increase the contrast as high as1.25times that of bright-filed image, the enhancement effect can increase the contrast as high as one time that of bright-filed image. For the non-metal plystyrene spheres, the contrast of fluorescence image is unchanged because there is no plasmonic coupling effect between the silver film and polystyrene spheres.The innovations of this thesis are shown as following:1. We find the thickness of silver nano-shell can influence the performance of optical sensor made of gold nanoparticles.. The experimental result shows when the gold nanorods with aspect ratio3.0is coated with silver shell of5nm thickness, the RIS of the sensor can reach321nm/RIU. And the FOM can reach4.0which is74%higher than that of uncoated gold nanorods; 2. We present a new type dual-layer structure composed of silver nanocubes and silver grating which can highly increase the SERS intensity. The SERS intensity collected from this dual-layer structure is196times larger than that from the single-layer structure composed of only one dimensional silver grating. The intensity of the Raman signals from this dual-layer structure is also14times larger than that from the dual-layer structure composed of silver nanocubes and silver film. The result is helpful for exploiting low cost, simple construction, good repeatability and highly sensitive SERS sensor or detection chip;3. We present the "sandwich" structure composed of metal-dielectric-metal which can increase the contrast of fluorescence image. We find that the thickness of dielectric layer can control the quenching or enhancement of the fluorescence. We also find that whether the fluorescence is quenched or enhanced, the contrast of fluorescence image of metallic nano-structure can be increased. The quenching effect can increase the contrast as larger as1.25times that of bright-fifed image, and the enhancement effect can increase the contrast as large as one time that of corresponding bright-filed image.更多还原