【作者】 陶文玉；

【导师】 赵爱武；

【作者基本信息】 中国科学技术大学 ， 无机化学， 2014， 博士

【摘要】 表面增强拉曼散射(SERS)的灵敏度极高,能在分子水平上给出关于物质的结构、吸附状态等方面的丰富信息,在分析化学、生物医学以及食品安全监测等领域受到广泛的关注。SERS基底的制备一直是该领域的一个研究热点,因为基底的表面形貌和材质等因素能够影响光谱的信号强度和重现性,从而决定了SERS这种检测方法在实际生活中的应用。制备SERS基底的主要原则是提高活性、稳定性和重现性并且降低成本。化学法具有快速简单的优点,可以在短时间内获得大量的金属纳米粒子。但是化学合成过程中往往需要加入一些表面活性剂作为稳定剂或者模板以诱导纳米颗粒更好地生长。吸附在金属颗粒表面的这些表面活性剂势必会影响到基底的SERS活性并干扰分析,所以干净绿色的化学合成法是一种挑战。物理法常用于制备有序金属基底,即在结构规则的模板上直接沉积金属层。这种方法制备的SERS基底重现性比较好,且具有干净的表面,更有利于探针分子的吸附和检测,同时也减少了信号干扰,近年来发展迅速。本论文利用化学法和物理法制备出了几种不同的贵金属SERS基底。主要创新成果如下：(1)提出一种快捷方便的高效绿色方法来合成纳米金树枝,即利用铝片置换还原氯金酸。获得的金树枝具有很好的结晶性且纯度很高。通过观察不同反应时间所得产物的形貌,推测了金纳米树枝的生长过程和生长机理。这种金纳米树枝具有较好的SERS活性,以对巯基苯胺作为拉曼探针分子,检测限可达10-9M。同时,该纳米树枝也具有很好的催化活性,可快速催化硼氢化钠还原对硝基苯酚生成对氨基苯酚的反应。(2)设计并制备了银纳米碟阵列作为新型SERS基底。纳米碟由纳米环和薄膜组成,其SERS增强能力约为纳米环的7倍。通过三维时域有限差分法模拟了两种结构的电磁场分布,发现纳米环阵列的电磁场增强主要集中于环的尖端和相邻环的缝隙间,而纳米碟的腔内电磁场也得到显著增强,且分布均匀。纳米碟阵列对农药福美双的检测限低至1×10-7M,达到超痕量检测标准。在纳米碟阵列上随机抽取9个点测量了罗丹明6G的SERS谱图,计算得到各谱图信号强度的相对标准偏差小于15%,表明其优秀的重现性。这种纳米碟结构在SERS检测分析以及相关器件设计方面具有巨大的应用潜力。(3)在银纳米球壳阵列表面沉积较薄的金膜获得双金属结构,提高了银基底的稳定性。首先利用粒径分别为500,440,360nm的二氧化硅微球为模板,沉积银纳米薄膜得到一系列的银纳米壳SERS活性基底。然后在活性最强的银壳上分别溅射不同厚度的金薄膜制备金银双金属壳层结构。SERS检测发现,金银双金属纳米壳层结构在532nm激光下拉曼增强效果远不如银纳米壳结构,但在780nm激光下具有很好的SERS活性,并且随着金层厚度的减小SERS信号强度逐渐增强。由于金的高稳定性和良好的生物相容性,该基底在SERS生物传感方面具有很大的潜在应用价值。(4)以二氧化硅小球为掩模板,采用电感耦合等离子体ICP)刻蚀硅片得到三维纳米柱和纳米锥阵列。反应刻蚀时间为120,210和360s时,得到的是纳米柱结构,当刻蚀了450s时,纳米柱演变成纳米锥结构。在纳米柱/锥阵列上沉积银膜可作为SERS基底,以对巯基苯胺为探针分子检测了其SERS活性,发现刻蚀时间为210s的纳米柱结构具有最好的性能。另外,这种阵列结构还具有很好的超疏水性能,可用于组装上银纳米颗粒以进一步提高SERS活性。更多还原

【Abstract】 Surface-enhanced Raman scattering (SERS) has very high sensitivity, it can supply a wealth of information about the structure and adsorption states of matter at the molecular level and has been widely concerned in the area of analytical chemistry, biomedicine, food safety monitoring and etc. The preparation of SERS substrates has been a hot topic in the field of SERS because the surface morphology and material of the substrate determine the signal strength and reproducibility of the spectrum, which has an important effect of the pratical applications of SERS detection in daily life. The main principle to prepare SERS substrates is to improve their activitiy, stability and producibility as well as to lower the cost. Chemical methods have the advantages of speediness and simpleness. A large number of metal nanoparticles could be obtained in a short time. However, the chemical synthesis processes often involve the addition of some surfactants as templates or stabilizers to induce the growth of nanoparticles. The surfactants adsorbed on the surface of the metal nanoparticles will weaken the SERS activities and interfere with the SERS analysis. Therefore, the development of a clean and green chemical synthesis method is a challenge. Physical methods are usually used to fabricate ordered metal substrates, namely direct deposition of metal layer onto templates with regular structures. SERS substrates prepared by this method have better reproducibilites and cleaner surfaces which are more conducive to the adsorption and detection of probe molecules and will reduce the signal interference. During recent years, physical methods have got rapid development. In this paper, we use both chemical and physical methods to prepare several different noble metal SERS substrates. The main innovative results are as follows:(1) A facile, efficient and green route was proposed to fabricate Au nanodendrites by reducing chloride acid with Al foil. The obtained Au dendrites have good crystallinity and high purity. Through a series of time-dependent morphological evolution experiments, the possible growth process and mechanism were proposed. The as-prepared Au dendrites exhibit excellent surface enhanced Raman scattering enhancement ability for detecting p-aminothiophenol molecules with a detection limit of10"9M. Moreover, they also display high catalytic activity through the quick reduction of p-nitrophenol by sodium borohydride.(2) Ag nanodish arrays were designed and fabricated as novel SERS substrates. The nanodishes were composed of nanorings and a film. They have a seven times SERS enhancement ability than nanorings. The electromagnetic field distributions of the two structures were simulated by three-dimensional finite-difference time-domain method. The simulation results show the electromagnetic field mainly locates at the tips of every single ring and the junctions among adjacent nanoparticles for the nanoring array. For nanodishes, an extra strong electromagnetic field appeared in the cavity and distributed uniformly. The detection limit for thiram from the nanodish array is as low as1×10-7M, which has achieved the ultra trace detection standard. The calculated relative standard deviation of the Raman signal intensity of rhodamine6G measured from nine randomly selected points is less than15%, indicating the excellent reproducibility. The nanodishes have great potential for applications in SERS detection analysis and related devices design.(3) Bimetallic structures were obtained by deposition a thin Au film onto Ag nanoshell array to improve the stability of Ag substrate. Firstly, a series of Ag nanoshells were prepared as SERS substrates by sputtering silver films on silica sphere templates with different sizes of500,440and360nm. Then Au films with different thicknesses were deposited on the the Ag nanoshells with the best activity to obtain Au-Ag bimetallic nanoshells. The SERS detection results revealed that the Au-Ag bimetallic nanoshells have much weaker Raman enhancement than Ag nanoshells when the laser wavelength was532nm but have excellent SERS activities under the excitation light of780nm wavelength. The SERS intensities from Au-Ag bimetallic nanoshells got enhanced as the decreasing of the thicknesses of the outer Au shells. The good stability and biocompatibility of Au confirms the Au-Ag bimetallic nanoshells have enormous potential application value in SERS biosensing.(4)Three dimensional nanopillar and nanocone arrays were fabricated by inductively coupled plasma etching of silicon slices with silica spheres as mask templates. When the etching time was120,210and360s, nanopillars were obtained. When the etching time was450s, the pillars will evolve into cone structures. Silver films were deposited onto the nanopillars/cones as SERS substrates. The detection results show that the samples etched210s exhibit the best performances. In addition, the arrays possess excellent super-hydrophobic properties, which may be used to self-assemble silver nanoparticles to improve their SERS activities further.更多还原