具有双共振吸收峰的Au纳米粒子制备及其拉曼表征

表面增强拉曼散射(SERS)很大程度的弥补了拉曼散射强度弱的缺点,迅速成为科研工作者们的研究热点,在食品安全、环境污染、毒品以及爆炸物检测等领域应用广泛。纳米技术的发展使得目前对于SERS的研究主要集中于金属纳米颗粒基底的制备,金属纳米粒子的种类、尺寸及形貌对SERS增强和吸收峰峰位均有影响,要获得好的增强效果,需要对金属纳米结构进行工艺优化。特别是,需要结合金属纳米粒子的结构和激励光波长,以期获得更好的增强效果。为了研究SERS增强和吸收峰之间的关系,开展了具有双共振吸收峰的金属纳米粒子的研究。首先利用FDTD Solutions仿真建模,主要针对金纳米颗粒直径、金纳米棒长径比及分布状态对共振吸收峰进行仿真,得到金纳米球理论直径在50 nm左右,金纳米棒理论长径比在3.5~4.5左右时,吸收峰分别分布在532及785 nm附近,符合多波段激励光拉曼增强条件;对于激励光偏振方向,其沿金纳米棒长轴方向偏振时吸收峰位于785 nm附近,沿金纳米球短轴方向偏振时吸收峰位于532 nm附近。然后采用种子生长法,制备了可用于多种波长激励光的双吸收峰表面增强拉曼散射基底。通过改变硝酸银用量(5,10,20,30和40 μL)、盐酸用量(0.1和0.2 mL)以及其生长时间(15,17,21和23 h)等多种工艺参数来控制金纳米棒含量,得到了同时含有金纳米球及金纳米棒的双吸收共振峰金纳米粒子。最后用该样品作为基底,罗丹明6G(R6G)作为探针分子,分别测试其在532,633和785 nm激励光入射时的SERS表征,对分析物R6G最低检测浓度均达到了10-7 mol·L-1,增强因子达到了~105,满足了多波段SERS检测的需要。     

不同粒径、超均匀球形金纳米粒子合成及其表面增强拉曼散射效应研究

以氯金酸为原料,抗坏血酸为还原剂,柠檬酸钠为保护剂,用化学还原(种子生长)法制备了不同粒径、超均匀的球形金纳米粒子溶胶,并通过紫外可见吸收光谱(UV-Vis)和扫描电子显微镜(SEM)进行表征。结果表明,随着金纳米粒子粒径的增大,其UV-Vis光谱中的吸收峰发生红移并出现四极峰。为进一步研究金纳米粒子表面增强拉曼散射(SERS)效应的作用机理并优化其灵敏度,我们以罗丹明6G(R6G)为探针分子,对不同粒径的金纳米粒子进行SERS表征,发现R6G的SERS信号随着金纳米粒子的增大先增强后减弱。当金纳米粒子的平均粒径达到120 nm时,产生最强SERS信号增强,增强因子约为1.1×107。三维时域有限差分法(3D-FDTD)理论模拟纳米粒子阵列电磁场分布结果与实验数据的趋势一致。     

DNA模板自组装正电荷纳米金基底的增强SERS效应

本文将合成的直径为10 nm的正电荷金纳米颗粒通过静电作用高密度自组装到带负电荷的长链λ-DNA分子上, 形成了高密度的具有纳米间隙的金纳米颗粒网络结构。研究了孤立的金纳米颗粒和所自组装的金纳米颗粒-DNA复合材料作为表面增强拉曼散射(SERS)基底的活性。原本对SERS信号响应较弱的10 nm直径的金纳米颗粒, 在自组装到DNA上形成具有纳米间隙的金纳米颗粒网络后, 产生了均匀、一致、强烈的SERS增强响应。我们利用用该基底对罗丹明G(R6G)、吡啶(Py)和对巯基苯胺(4-ATP)等不同类型的小分子化合物进行SERS检测的结果表明, 此方法制备SERS基底产率高、均一, 具有较好的SERS增强效果好, SERS信号稳定性和重复性相对常规孤立的金纳米颗粒SERS基底有很大提高。     

金银双金属纳米壳层结构的SERS活性研究

利用磁控溅射技术在组装整齐的微球表面依次镀上银、金薄膜,获得双金属纳米壳层结构。以对巯基苯胺(p-ATP)为探针分子,研究了该壳层结构在不同激发线下SERS增强差异。测试结果表明,金银双金属纳米壳层结构在780nm激光下具有很好的SERS增强效果,并随着外层金膜厚度的减小而逐渐增强。对各个基底的增强因子进行计算可知,基底的表面等离子体共振(SPR)峰与激发线的匹配程度越好,其增强因子越大。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应用潜力。     

聚甲基丙烯酸甲酯间隔的金纳米立方体与金膜复合结构的表面增强拉曼散射研究

金属纳米颗粒与金属薄膜的复合结构由于其局域表面等离子体和传播表面等离子体间的强共振耦合作用,可作为表面增强拉曼散射(SERS)基底,显著增强吸附分子的拉曼信号.本文提出了一种聚甲基丙烯酸甲酯(PMMA)间隔的90 nm金纳米立方体与50 nm金膜复合结构的SERS基底,通过有限元方法数值模拟,得到PMMA的最优化厚度为15 nm.实验制备了PMMA间隔层厚度为14 nm的复合结构,利用罗丹明6G (R6G)为拉曼探针分子, 633 nm的氦氖激光器作为激发光源,研究了复合结构和单一金纳米立方体的SERS效应,发现复合结构可以使探针分子产生比单一结构更强的拉曼信号.在此基础上,研究了不同浓度金纳米立方体水溶液条件下复合结构中R6G的拉曼光谱.结果表明,当金纳米立方体水溶液浓度为5.625μg/mL的条件下复合结构中R6G的拉曼信号最强,且可测量R6G的最低浓度达10~(–11) mol/L.     

利用AAO模板制备SERS基底检测SudanⅠ

通过模板法制备大面积、可控的、可重复的、热点集中的金纳米结构阵列,并在纳米结构阵列上通过化学修饰分子,吸附更多苏丹红Ⅰ分子至金纳米的SERS增强区域,实现其高灵敏的表面增强拉曼分析检测。以多孔阳极氧化铝为模板,通过真空蒸镀金,约200 nm厚度,复制氧化铝的孔洞结构,用碱液将氧化铝模板腐蚀去除,可得到氧化铝模板的互补结构,即大面积的、均匀的金半球纳米结构阵列。在金纳米结构阵列上修饰十二硫醇,硫醇巯基端与纳米金相结合,碳链端自组装形成非极性的疏水环境,疏水环境可以捕获苏丹红Ⅰ分子,使其吸附至纳米金结构表面的SERS增强区域,实现苏丹红Ⅰ的SERS检测。由于SERS基底表面的金半球纳米结构均匀、规整,在激光光斑的区域内,苏丹红Ⅰ的SERS信号均匀、稳定,可以对苏丹红Ⅰ进行定量分析。苏丹红Ⅰ的拉曼峰强度对数与浓度对数之间呈线性关系,线性相关系数达0.99,线性范围为5×10-4～10-7mol·L-1,回收率范围77%～117%。此方法的检测限可达到4×10-8mol·L-1,与国标的高效液相色谱的检测限相当。     

不同形状的金纳米粒子的表面增强拉曼光谱

使用514 5nm激光激发,第一次得到了不同形状金纳米粒子的表面增强拉曼光谱(SERS)。一般情况下,较短波长(<600nm)激发所获得的增强要小于使用较长波长(>600nm)的激发。然而,对特殊形状的自组装金纳米粒子,由于避雷针效应,即使使用绿光激发也可获得很高增强的SERS。     

785nm激光诱导银纳米三角片聚集表面增强拉曼散射效应

为实现表面增强拉曼散射(SERS)光谱的强信号快速检测分析,报道了通过785 nm激光诱导银纳米三角片(AgNPRs)聚集的方法。采用配体辅助化学还原法制备了AgNPRs,其边长约为80 nm,表面等离子体吸收峰出现在约774 nm处,对785 nm光产生有效吸收。在785 nm光辐照下,AgNPRs逐渐聚集,对巯基苯甲酸的SERS信号逐渐增强,其源于AgNPRs吸收的光转化为热而引起的AgNPRs聚集。其增强因子高达109。为快速获得强SERS信号,激发光功率需大于250 mW。     

金纳米粒子的制备及其表面增强拉曼散射效应的研究

采用多巴胺化学还原法制备了分散性良好的纳米金溶胶,并检测了其作为表面增强拉曼散射(Surface Enhanced Raman Scattering,SERS)基底的性质。粒度和透射电子显微镜测试结果表明金溶胶为平均粒径30nm左右的球形颗粒,并且紫外-可见特征吸收峰出现在520nm,为典型的金纳米颗粒特征吸收峰。以罗丹明6G(R6G)为探针分子证明了金溶胶良好的SERS增强效果,用金溶胶对除草剂敌草快(DQ)进行检测,最低检测限可达1×10-7 mol/L。结果表明所制备的金溶胶具有良好的表面增强拉曼散射活性。     

三维时域有限差分法计算金纳米粒子尺寸与SERS活性的关联

通过合成一系列不同粒径(16～160 nm)的金纳米粒子.观察到120～135 nm的金纳米粒子在632.8nm波长激发下具有最高的SERS活性,这与前人报道的电磁场理论及实验的结果不同.利用三维时域有限差分法对金纳米粒子的SERS活性与其尺寸以及入射光波长的关系进行模拟计算.在632.8 nm激发线下,金纳米粒子二聚体体系在粒径为110 nm左右具有最佳增强效应,其光电场耦合最强的热点处的增强因子高达109考虑到体系的平均SERS增强因子通常会比最大值低约2个数量级,计算得到的107的增强因子与实验测量值相符.同时对目前实验上尚难以合成的大尺寸的金纳米粒子进行模拟,结果表明受多极矩和大尺寸效应的影响在粒径220 nm时又出现SERS增强另一峰值.在325 nm的紫外激发线下,计算得到的增强因子仅为102.     

Facile preparation of Au/Ag bimetallic hollow nanospheres and its application in surface-enhanced Raman scattering

In this paper, an Au/Ag bimetallic hollow nanostructure was obtained by using SiO₂ nanospheres as sacrificial templates. The nanostructure was fabricated via a three steps method. SiO₂@Au nanospheres were first synthesized by the layer-by-layer technique, and then they were coated with a layer of Ag particles, finally, the Au/Ag bimetallic hollow nanospheres were obtained by dissolution of the SiO₂ core by exposure in HF solution. Several characterizations, such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and UV visible absorption spectroscopy were used to investigate the prepared nanostructures. The effectiveness of these Au/Ag bimetallic hollow nanospheres as substrates toward surface-enhanced Raman scattering (SERS) detection was evaluated by using rhodamine 6G (R6G) as a probe molecule. We show that such Au/Ag bimetallic hollow nanospheres structure films which consisting of larger interconnected aggregates are highly desirable as SERS substrates in terms of high Raman intensity enhancement. The Au/Ag bimetallic hollow nanostructured aggregate, interconnected nanostructured aggregate and nanoscale roughness are important factors responsible for this large SERS enhancement ability.     

Influence of two different template removal methods on the micromorphology,crystal structure,and photocatalytic activity of hollow CdS nanospheres

Hollow cadmium sulfide (CdS) nanospheres of about 260 nm average diameters and about 30 nm shell thickness can be easily synthesized via a sonochemical process, in which polystyrene (PS) nanoparticles were employed as templates. In order to remove the PS templates, both etching and calcination were applied in this paper. The influence of the two different template removal methods on the surface micromorphology, crystal structure, and photocatalytic activity of hollow CdS nanospheres was carefully performed a comparative study. Results of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray, FT-IR, thermogravimetric analysis, Brunauer–Emmett–Teller, diffused reflectance spectra, and decolorization experiments showed that the different template removal methods exhibited a significant influence on the surface micromorphology, crystal structure, and photocatalytic activity of hollow CdS nanospheres. The CdS hollow nanospheres as-prepared by etching had pure cubic sphalerite structure, higher –OH content, less defects and exhibited good photocatalytic activity for rhodamine-B, Methylene Blue and methyl orange under UV–vis light irradiation. However, CdS hollow nanospheres obtained by calcination with a hexagonal crystal structure, less –OH content, more defects have shown worse photocatalytic activity. This indicated that surface micromorphology and crystalline phase were mainly factors influencing photocatalytic activity of hollow CdS nanospheres.     

Laser tattoo removal as an ablation process monitored by acoustical and optical methods

Monodisperse hollow silica nanospheres have been prepared by using a polystyrene nanosphere template-assistant approach and their potential as antireflection (AR) coatings for window applications has been discussed. The as-prepared hollow silica nanospheres have a typical inner diameter of 200 nm and a shell thickness of 15–20 nm. The AR effect over the ultraviolet-visible-near infrared spectral region has been observed for the hollow silica nanospheres, with a minimized reflection of about 5.2 % at 500 nm, compared to 8.5 % of a plain float glass substrate. By modifying the structural features of the hollow silica nanospheres, their AR properties can be further enhanced.     

SERS enhancement of gold nanospheres of defined size

Monodisperse, citrate‐stabilized gold nanoparticles of sizes ranging from 15 to 40 nm were synthesized and characterized by small angle X‐ray scattering and UV‐vis experiments. Identical surface properties of nanoparticles of different sizes to avoid variation in the chemical surface‐enhanced Raman scattering (SERS) enhancement, as well as selection of experimental conditions so that no aggregation took place, enabled the investigation of enhancement of individual nanospheres. Enhancement factors (EFs) for SERS were determined using the dye crystal violet (CV). EFs for individual gold nanospheres ranged from 10² to 10³, in agreement with theoretical predictions. An increase of the EFs of individual spheres with size can be correlated to changes in the extinction spectra of nanoparticle solutions. This confirms that the increase in enhancement with increasing size results from an increase in electromagnetic enhancement. Beyond this dependence of EFs of isolated gold spheres on their size, EFs were shown to vary with analyte concentration as a result of analyte‐induced aggregation. This has implications for the application of nanoparticle solutions as SERS substrates in quantitative analytical tasks. Copyright © 2011 John Wiley & Sons, Ltd.     

A self-generated template route to hollow carbon nanospheres in a short time

A self-generated template route was reported to prepare hollow carbon nanospheres. The hollow spheres were obtained through the direct pyrolysis of ferrocene for 1 h. The external diameter of the hollow carbon nanospheres was 50-150 nm and the thickness of the wall was about 15 nm. A possible formation mechanism of the hollow carbon nanospheres was discussed.     

Synthesis and formaldehyde sensing performance of LaFeO3 hollow nanospheres

Metal oxide semiconductors with hollow structure and morphology have attracted considerable attentions because of their promising application on gas sensors. In this paper, LaFeO₃ hollow nanospheres have been prepared by using carbon spheres as templates in combination with calcination. Based on the observation of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and transmission electron microscope (TEM), the structure and morphology of the products were characterized. It has been revealed that as-prepared LaFeO₃ samples have a uniform diameter of around 300 nm and hollow structures with thin shells of about 30 nm consisting of numerous nanocrystals and nanopores. Owing to the hollow and porous structure, large surface area and more surface active sites, the sensor based on LaFeO₃ hollow nanospheres exhibited high response, good selectivity and stability to formaldehyde gas (HCHO). It suggests that the as-prepared LaFeO₃ hollow nanospheres are promising candidates for good performance formaldehyde sensor.     

Enhancement in SERS intensity with hierarchical nanostructures by bimetallic deposition approach

We investigate the plasmonic enhancement arising from bimetallic (Au/Ag) hierarchical structure and address the fundamental issues relating to the design of multilayered nanostructures for surface‐enhanced Raman scattering (SERS) spectroscopy. SERS‐active nanosphere arrays with Ag underlayer and Au overlayer were systematically constructed, with the thickness of each layer altered from 40 to 320 nm. The SERS responses of the resultant bimetallic structures were measured with 2‐naphthalenethiol dye as the test sample. The results confirm the dependency of SERS enhancement on the thickness ratio (Au : Ag). Compared with Au‐arrays, our optimized bimetallic structures, which exhibit nanoprotrusions on the nanospheres, were found to be 2.5 times more SERS enhancing, approaching the enhancement factor of an Ag‐array. The elevated SERS is attributed to the formation of effective hot‐spots associated with increased roughness of the outer Au film, resulting from subsequent sputtering of Au granules on a roughened Ag surface. The morphology and reflectance studies suggest that the SERS hot‐spots are distributed at the junctions of interconnected nanospheres and over the nanosphere surface, depending on the thickness ratio between the Au and Ag layers. We show that, by varying the thickness ratio, it is possible to optimize the SERS enhancement factor without significantly altering the operating plasmon resonance wavelength, which is dictated solely by the size of the underlying nanospheres template. In addition, our bimetallic substrates show long‐term stability compared with previously reported Ag‐arrays, whose SERS efficiency drops by 60% within a week because of oxidation. These findings demonstrate the potential of using such a bimetallic configuration to morphologically optimize any SERS substrate for sensing applications that demand huge SERS enhancement and adequate chemical stability. Copyright © 2011 John Wiley & Sons, Ltd.     

Controlling SERS intensity by tuning the size and height of a silver nanoparticle array

It is demonstrated that the surface-enhanced Raman scattering (SERS) intensity of R6G molecules adsorbed on a Ag nanoparticle array can be controlled by tuning the size and height of the nanoparticles. A firm Ag nanoparticle array was fabricated on glass substrate by using nanosphere lithography (NSL) combined with reactive ion etching (RIE). Different sizes of Ag nanoparticles were fabricated with seed polystyrene nanospheres ranging from 430 nm to 820 nm in diameter. By depositing different thicknesses of Ag film and lifting off nanospheres from the surface of the substrate, the height of the Ag nanoparticles can be tuned. It is observed that the SERS enhancement factor will increase when the size of the Ag nanoparticles decreases and the deposition thickness of the Ag film increases. An enhancement factor as high as 2×10⁶ can be achieved when the size of the polystyrene nanospheres is 430 nm in diameter and the height of the Ag nanoparticles is 96 nm. By using a confocal Raman mapping technique, we also demonstrate that the intensity of Raman scattering is enhanced due to the local surface plasmon resonance (LSPR) occurring in the Ag nanoparticle array.     

A high‐throughput method for controlled hot‐spot fabrication in SERS‐active gold nanoparticle dimer arrays

We present a high‐throughput method for fabricating large arrays of surface‐enhanced Raman scattering (SERS) active gold dimers. Using a large‐area/low‐cost nanopatterning method in conjunction with a meniscus force deposition technique, we were able to create large arrays of uniformly spaced nanoclusters comprising two 60‐nm gold nanospheres. Raman measurements of a thiophenol monolayer deposited on smaller scale arrays of aligned dimers yielded enhancement factors as high as 10⁹. Polarization‐controlled measurements show spectral peak heights to be 10–100 times smaller when the incident beam is polarized perpendicularly to the dimer axis, confirming that the measured enhancements arise from the ‘hot spots’ between the two nanospheres. Copyright © 2009 John Wiley & Sons, Ltd.