金属纳米结构表面的可控制备及其在光学检测中的应用

发布时间：2018-08-22 16:02

【摘要】：金属纳米结构的表面等离子共振(surface plasmon resonance,SPR)性质可以简单地理解为金属内的自由电子受到入射光的电场驱使,发生相对于金属离子骨架的集体振荡,直观表现为对特定频率的光的吸收和散射。SPR性质强烈依赖于金属纳米结构的几何参数、周围环境以及相邻金属纳米结构的间距和排列方式。基于高度可调的SPR性质,以及伴随产生的局部电磁场增强等现象,纳米尺度的金属结构在传感器、表面增强光谱、能量转换等众多领域展现出了广阔的应用前景。但是目前很多应用尝试依然存在明显的缺陷,制约其进一步走进生产生活。例如在光学检测领域,很多已报道的SPR传感器除了受到灵敏度的限制以外,其用于检测的共振峰通常都比较宽。这导致传感器光谱分辨率不足,不利于被测物浓度极低时,微小位移的确定;SERS基底的均一性也限制很多高活性基底在检测中,特别是定量检测中发挥作用。虽然包括上述在内的一些由结构本身的缺陷所导致的问题,通常可以利用高精度的“由上而下”的技术手段优化结构来解决,但是这类方法往往因高成本、低效率等问题为人诟病。因此,制约应用的第二个方面便是制备方法。出于上述动机,本论文经过合理设计,并借助高效低成本的胶体刻蚀和静电自组装技术,制备了一系列基于金属纳米结构表面的高性能光学检测平台,为实际应用打下良好基础。在第二章中,我们利用胶体刻蚀技术制备了一种基于简单的二维银纳米井阵列的高性能SPR传感器。其结构可以视为有序的银纳米孔阵列与平整的银膜贴合而成。银纳米井的二维金属光栅结构使入射光在遵从Bragg衍射条件的前提下,与金属表面更高效率地耦合,形成表面等离子激元(surface plasmon plaritons,SPPs)。同时,由SPPs引起的增强电磁场完全处于纳米井与空气的界面处,这样能够保证环境的变化被充分感知,避免了基底效应带来的负面影响。而且利用灵活的胶体刻蚀技术,纳米井的几何参数可以很方便地调节,优化传感器性能。我们先通过改变干法刻蚀时间和第一次沉积的金属厚度分别对纳米井的孔径和深度进行优化,得到了强而锐的峰形。其中,孔径的调节直接影响到SPPs和瑞利奇异的耦合效应,该现象的存在对缩减半峰宽至关重要。另外,利用更大尺寸的胶体微球掩板,增大阵列的晶格常数,可以提高传感器的折射率灵敏度。与此同时,我们进行了精密的电磁学仿真,以证实实验结果的可靠性,并辅助参数优化。优化之后的样品具有很高的折射率灵敏度和极窄的半峰宽,使其成为高灵敏度和高分辨率兼备的高性能spr传感器。最后的免疫试验表明,优化后的银纳米井阵列可以作为优异的生物分子检测平台。此外,在银纳米井的基础之上,我们在银膜和纳米孔阵列之间构筑不同厚度的介电层,从而衍生出了一种银纳米孔阵列-介电层-银膜“三明治”型复合结构。通过光学表征以及理论仿真,我们发现在银纳米孔与银膜之间会形成共振腔,其共振模式所对应的光谱中的吸收峰会随着介电层厚度的变化而发生峰位的移动,并且位移值与厚度具有明确的指数函数关系。因此,这样一种结构可以用作对距离敏感的等离子体尺(plasmonruler)。在第三章中,我们利用带电荷金属纳米球粒子的静电自组装,结合金属垂直沉积的方法,制备了一种基于金属纳米粒子-纳米孔杂化结构阵列的高活性和高均一性的sers基底。通过精确控制银的沉积厚度,可以在金属纳米球和纳米孔之间形成足够窄的环形缝隙,为sers提供高增强因子的“热点”。而为了达到高度的均一性,我们从以下三个方面进行了设计。首先,本章使用的金纳米球是利用种子生长法制备的,具有规整的形貌和出色的单分散性,这使得环形纳米缝隙的尺寸比较均匀。其次,较低的离子强度使得通过静电引力吸附在基底上的金纳米粒子间距较大,几乎没有耦合作用,从而避免了平面内粒子间形成的分布不均的“热点”。最后,虽然金纳米球在基底上的排列不是长程有序的,但是它们分布均匀,因此在任何位置,激光的圆形光斑所照射到的环形缝隙数目几乎相同。基于上述四个条件,我们所制备的金属纳米粒子-纳米孔杂化结构表面可以兼具出色的增强效果和均一性。此外,本章所采用的方法简单,成本低廉,更能实现大面积的制备,这使得我们的方法在实际应用当中具有极大优势。在第四章中,我们发展了一种简单的方法,用以制备粒子间距和光学性质高度可调的大面积二维金纳米粒子阵列,并且通过这种方法可以十分简便地将这些性质以梯度的形式集成在一个基底上。粒子的间距决定于基底的电荷密度,而电荷密度的调节利用了聚合物的流变性质。电中性的聚苯乙烯(ps)薄膜通过氧气等离子体处理后,表面产生极性的含氧基团,使其能够进行静电吸附。由于极性的含氧基团具有较高的表面自由能,因而当聚合物受热,发生链段运动时,这些基团会倾向于远离薄膜和空气界面,进入ps薄膜内部,以降低表面能。这样一来,我们就可以在不同温度下对氧气等离子体处理后的PS薄膜进行热退火处理,并结合层层静电自组装,得到电荷密度不同的表面。这些表面最终可以吸附得到不同粒子间距和光学性质的金纳米粒子阵列。而由于粒子间距对局域表面等离子共振(localized plasmon resonance,LSPR)耦合的重要影响,不同间距的样品在光谱上也呈现出高度可调性。光谱中存在多重共振模式,从而可以支持波长选择的多重SERS信号,有利于匹配LSPR共振带、激发波长以及被测物。在退火步骤中,采用具有表面温度梯度的热源,就可以简单地制备出大面积的具有梯度变化的粒子间距和光谱的二维金属纳米粒子阵列。这种梯度表面可以作为一个“库”,用在特定的应用中对粒子间距或者光谱的快速筛选。我们的方法简单、通用、可大面积制备,并且无需任何昂贵精密的仪器,因而适用于普通的实验室和大规模生产。
[Abstract]:Surface plasmon resonance (SPR) properties of metal nanostructures can be simply understood as the collective oscillation of free electrons driven by the electric field of incident light relative to the metal ion skeleton. SPR properties are strongly dependent on metal nanoparticles. Based on the highly adjustable SPR properties and the accompanying local electromagnetic field enhancement phenomena, nano-scale metal structures have shown broad application prospects in many fields such as sensors, surface enhancement spectroscopy, energy conversion and so on. For example, in the field of optical detection, many reported SPR sensors are usually used to detect the formant of a wide range, except for the limitation of sensitivity. This leads to the lack of spectral resolution of the sensor, which is not conducive to the detection of the concentration pole. The homogeneity of SERS substrate also limits the role of many highly active substrates in testing, especially in quantitative testing. Although some of the problems caused by structural defects, including the above, can usually be solved by high-precision "top-down" technical means to optimize the structure, but For these reasons, a series of high-performance optical detectors based on metal nanostructures have been fabricated by rational design, high-efficiency and low-cost colloid etching and electrostatic self-assembly techniques. In the second chapter, a high performance SPR sensor based on a simple two-dimensional silver nanowell array is fabricated by using colloid etching technique. The structure of the sensor can be regarded as an ordered array of silver nanoholes bonded to a flat silver film. On the premise of following Bragg diffraction condition, the surface plasmon plaritons (SPPs) are formed by coupling with metal surface more efficiently. Meanwhile, the enhanced electromagnetic field caused by SPPs is completely located at the interface between nano-well and air, which can ensure that the change of environment is fully perceived and avoid the negative effect of substrate effect. The geometric parameters of the nanowells can be easily adjusted to optimize the performance of the sensors by using flexible colloid etching technology. We first optimize the pore size and depth of the nanowells by changing the dry etching time and the first deposited metal thickness, and then obtain a strong and sharp peak shape. The coupling effect between SPPs and Rayleigh singularity is very important for reducing the half-peak width. In addition, the refractive index sensitivity of the sensor can be improved by increasing the lattice constant of the array with a larger size of colloidal microsphere mask. At the same time, we have carried out a precise electromagnetic simulation to verify the reliability of the experimental results. The optimized samples have high refractive index sensitivity and very narrow half-peak width, making them high-sensitivity and high-resolution SPR sensors. The final immune test shows that the optimized silver nanowell array can be used as an excellent platform for biomolecular detection. On this basis, we construct different thickness dielectric layers between silver film and nanopore array, and then derive a silver nanopore array-dielectric layer-silver film sandwich composite structure. In the third chapter, we use electrostatic self-assembly of charged metal nanospheres. A highly active and homogeneous SERS substrate based on metal nanoparticle-nanopore hybrid structure array was fabricated by combining metal vertical deposition method. In order to achieve a high degree of homogeneity, we designed the gold nanospheres from the following three aspects. Firstly, the gold nanospheres used in this chapter were prepared by seed growth method, with regular morphology and excellent monodispersity, which made the size of the annular nano-gap more uniform. Secondly, the lower ionic strength made them adsorbed by electrostatic gravity. Finally, although the gold nanospheres are not aligned in a long-range order on the substrate, they are evenly distributed, so at any location, the circular spot of the laser illuminates the annular gap. Based on the above four conditions, the surface of the metal nanoparticles-nanoporous hybrid structure can have both excellent enhancement effect and homogeneity. In addition, the method used in this chapter is simple, low cost, and can achieve large-area preparation, which makes our method has great advantages in practical application. In Chapter 4, we developed a simple method to fabricate two-dimensional gold nanoparticle arrays with highly tunable particle spacing and optical properties, which can be easily integrated in a gradient form on a substrate. The charge density modulation takes advantage of the rheological properties of the polymer. After the electroneutral polystyrene (ps) film is treated by oxygen plasma, polar oxygen-containing groups are formed on the surface to enable electrostatic adsorption. Groups tend to move away from the film-air interface and into the PS film to reduce surface energy. Thus, the PS film treated by oxygen plasma can be annealed at different temperatures, and the surface with different charge densities can be obtained by layer-by-layer electrostatic self-assembly. Gold nanoparticle arrays with the same particle spacing and optical properties. Due to the important influence of particle spacing on local surface plasmon resonance (LSPR) coupling, the samples with different particle spacing also exhibit a high degree of spectral tunability. There are multiple resonance modes in the spectrum, which can support multiple SERs for wavelength selection. S-signal is advantageous for matching LSPR resonance bands, excitation wavelengths, and measured objects. In the annealing process, a large area of two-dimensional metal nanoparticle arrays with gradient particle spacing and spectrum can be easily fabricated by using a heat source with a surface temperature gradient. The gradient surface can be used as a "library" for specific applications. Our method is simple, universal, and can be prepared in large areas without any expensive and precise instruments, so it is suitable for ordinary laboratories and large-scale production.
【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB383.1

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