Self-assembled Ag nanoparticles for surface enhanced Raman scattering

Uniform and reproducible substrates for surface enhanced Raman scattering (SERS) are fabricated by self-assembly of Ag nanoparticles (NPs) on 3-aminopropyltrimethoxysilane (APTES) modified glass. Experimental results indicate that the Ag NPs with a narrow size distribution were assembled as a sub-monolayer which exhibits an excellent SERSactivity. The SERS enhancement factor is estimated to be 7.5 × 10⁶ and the detection limit for crystal violet (CV) solution is about ～10^?11 M. The uniformity and reproducibility of the SERS signals are tested by point-to-point and batch-to-batch measurements. It is confirmed that the self-assembled Ag NPs substrates has a high SERS reproducibility and a low standard deviation with respect to the Ag NPs on non-functionalized glass substrates. The self-assembled Ag NPs substrates can be widely used for the application of chemical and biochemical sensing.     

Effect of different analyte diffusion/adsorption protocols on SERS signals

The effect of different analyte diffusion/adsorption protocols was studied which is often overlooked in surface-enhanced Raman scattering (SERS) technique. Three protocols: highly concentrated dilution (HCD) protocol, half–half dilution (HHD) protocol and layered adsorption (LA) protocol were studied and the SERS substrates were monolayer films of 80 nm Ag nanoparticles (NPs) which were modified by polyvinylpyrrolidone. The diffusion/adsorption mechanisms were modelled using the diffusion equation and the electromagnetic field distribution of two adjacent Ag NPs was simulated by the finite-different time-domain method. All experimental data and theoretical analysis suggest that different diffusion/adsorption behaviour of analytes will cause different SERS signal enhancements. HHD protocol could produce the most uniform and reproducible samples, and the corresponding signal intensity of the analyte is the strongest. This study will help to understand and promote the use of SERS technique in quantitative analysis.     

A facile method for the synthesis of large‐size Ag nanoparticles as efficient SERS substrates

Silver nanoparticles (Ag NPs) enjoy a reputation as an ultrasensitive substrate for surface‐enhanced Raman spectroscopy (SERS). However, large‐scale synthesis of Ag NPs in a controlled manner is a challenging task for a long period of time. Here, we reported a simple seed‐mediated method to synthesize Ag NPs with controllable sizes from 50 to 300 nm, which were characterized by scanning electron microscopy (SEM) and UV–Vis spectroscopy. SERS spectra of Rhodamine 6G (R6G) from the as‐prepared Ag NPs substrates indicate that the enhancement capability of Ag NPs varies with different excitation wavelengths. The Ag NPs with average sizes of ~150, ~175, and ~225 nm show the highest SERS activities for 532, 633, and 785‐nm excitation, respectively. Significantly, 150‐nm Ag NPs exhibit an enhancement factor exceeding 10⁸ for pyridine (Py) molecules in electrochemical SERS (EC‐SERS) measurements. Furthermore, finite‐difference time‐domain (FDTD) calculation is employed to explain the size‐dependent SERS activity. Finally, the potential of the as‐prepared SERS substrates is demonstrated with the detection of malachite green. Copyright © 2016 John Wiley & Sons, Ltd.     

基于气相沉积等离激元纳米粒子/三维石墨烯-镍泡沫复合结构的高灵敏度表面增强拉曼检测

本文提出一种基于气相沉积银纳米粒子和三维石墨烯-镍泡沫的复合等离激元结构.该结构是利用气相纳米团簇束流技术将高密度的银纳米粒子直接沉积于三维石墨烯-镍泡沫的表面制备而成.与传统银纳米结构相比,复合三维等离激元纳米结构具有"热点"数量多,局域场更强的特点,可作为基于表面增强拉曼技术的高灵敏度化学传感器.拉曼测试实验结果表明,该三维纳米结构在表面增强拉曼检测中可获得灵敏度高,重复性好的探针拉曼信号.通过进一步的理论模拟,发现该三维等离激元结构中增强的拉曼信号主要归因于纳米粒子与纳米粒子之间以及纳米粒子与石墨烯-镍泡沫衬底之间的多重近场耦合效应.     

In situ spectroelectrochemical surface-enhanced Raman scattering (SERS) investigations on composite Ag/TiO2-nanotubes/Ti substrates

A tubular array of TiO₂-nanotubes on a Ti substrate was used as a support for an Ag sputter-deposited layer intended for surface-enhanced Raman scattering (SERS) investigations. Composite samples of Ag/TiO₂-nanotube/Ti were studied with the aid of scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) to reveal their characteristic morphological and chemical features. Raman spectra of pyridine (as a probe molecule) were measured at different cathodic potentials ranging from −0.2 down to −1.2 V after the pyridine had been adsorbed on the TiO₂-nanotube/Ti substrates covered with the Ag deposit. In addition, SERS spectra on a bulk electrochemically-roughened Ag reference substrate, were also measured.The SERS activity of the composite samples was strongly dependent on the amount of Ag deposit and, in some cases, was even higher than that for the Ag reference substrate. The SERS intensity vs. electrode potential dependences measured were interpreted in terms of the modified electronic structure of the Ag deposits due to the interaction of the Ag clusters with the TiO₂-nanotube/Ti substrate.     

Large-scale fabrication of polymer/Ag core–shell nanorod array as flexible SERS substrate by combining direct nanoimprint and electroless deposition

We demonstrate a highly sensitive surface-enhanced Raman scattering (SERS) substrate, which consists of Ag nanoparticles (NPs) assembled on the surface of a nanopatterned polymer film. The fabrication route of a polymer/Ag core–shell nanorod (PACSN) array employed a direct nanoimprint technique to create a high-resolution polymer nanorod array. The obtained nanopatterned polymer film was subjected to electroless deposition to form a sea-cucumber-like Ag shell over the surface of the polymer nanorod. The morphology and structures of PACSNs were analyzed by using scanning electron microscopy and X-ray diffraction. The as-synthesized PACSNs exhibited a remarkable SERS activity and Raman signal reproducibility to rhodamine 6G, and a concentration down to 10^?12 M can be identified. The effect of electroless deposition time of Ag NPs onto the polymer nanorod surface was investigated. It was found that the electroless deposition time played an important role in SERS activity. Our results revealed that the combination of direct nanoimprint and electroless deposition provided a convenient and cost-effective way for large-scale fabrication of reliable SERS substrates without the requirement of expensive instruments.     

Facile synthesis of SERS active Ag nanoparticles in the presence of tri-n-octylphosphine sulfide

A facile and novel way was reported here for the synthesis of hydrophobic Ag nanoparticles (NPs), using AgNO₃, tri-n-octylphosphine (TOP) and sulfur (S) powder in process. TOP was used as solvent, reducing agent and stabilizer. S could chelate with excessive TOP to form trioctylphosphine sulfide (TOPS), which served as second capping agent. The hydrophobic Ag NPs could be transformed into hydrophilic state through ligand exchange. Furthermore, surface-enhanced Raman scattering (SERS) spectra of 4-aminothiophenol (4-ATP) were obtained on the hydrophobic and hydrophilic Ag NPs modified substrates, indicating that the as-synthesized Ag NPs had great potential for high sensitive optical detection applications.     

Diamine-linked array of metal (Au,Ag) nanoparticles on glass substrates for reliable surface-enhanced Raman scattering (SERS) measurements

Metal (Au, Ag) nanoparticles (M NPs) (ca. 30–40 nm) prepared by citrate reduction method were arrayed on amine-terminated glass substrates using diamine linkers with different chain lengths. 1,4-diaminobutane (C-4 diamine) produced the uniform and densely-packed array of M NPs on glass substrates at appropriate concentration ranges, whereas diamine linkers with longer chain lengths (C-8 and C-12 diamines) produced more heterogeneous and aggregated array of M NPs. When compared to Ag NPs, Au NPs demonstrated more controllable and higher packing density due to their mono-dispersed size and higher affinity to diamine linkers. Uniformly arrayed M NPs (Au, Ag) on glass substrates exhibited high enhancement factors in SERS measurements of o-chlorothiophenol probes. Au NPs arrayed substrates exhibited an approximate power-law linearity of Raman intensity with probe concentrations (from 10⁻⁷ M to 10⁻⁴ M), demonstrating more reliable SERS substrates than Ag arrayed substrates with higher SERS activity.     

Detection of breast cancer based on novel porous silicon Bragg reflector surface-enhanced Raman spectroscopy-active structure

In this Letter, the surface-enhanced Raman scattering(SERS) signal of early breast cancer(BRC) patient serum is obtained by a composite silver nanoparticles(Ag NPs) PSi Bragg reflector SERS substrate. Based on these advantages, the serum SERS signals of 30 normal people and 30 early BRC patients were detected by this substrate. After a baseline correction of the experimental data, principal component analysis and linear discriminant analysis were used to complete the data processing. The results showed that the diagnostic accuracy, specificity,and sensitivity of the composite Ag NPs PSi Bragg reflector SERS substrate were 95%, 96.7%, and 93.3%, respectively. The results of this exploratory study prove that the detection of early BRC serum based on a composite Ag NPs PSi Bragg reflector SERS substrate is with a stable strong SERS signal, and an unmarked and noninvasive BRC diagnosis technology. In the future, this technology can serve as a noninvasive clinical tool to detect cancer diseases and have a considerable impact on clinical medical detection.     

Enhancements in intensity and thermal stability of Raman spectra based on roughened gold substrates modified by underpotential deposition of silver

In this study, electrochemically roughened gold is modified with underpotential deposition (UPD) silver to investigate the effects on enhancements in the intensity and the thermal stability of surface‐enhanced Raman scattering (SERS). The SERS of Rhodamine 6G (R6G) adsorbed on the UPD Ag‐modified Au substrate exhibits a higher intensity by six‐fold of magnitude, as compared with that of R6G adsorbedon the unmodified Au substrate. Moreover, the SERS enhancement capabilities of UPD Ag‐modified Au and unmodified Au substrates are seriously depressed at temperatures higher than 200 and 150 °C, respectively. It indicates that the modification of UPD Ag can significantly depress the thermal destruction of SERS‐active substrates. Copyright © 2009 John Wiley & Sons, Ltd.     

PATP在Ag/TiO_2纳米管基底上的表面增强拉曼散射和光催化过程研究

表面增强拉曼散射(SERS)是一种超灵敏、高选择性的分析方法,越来越受到人们的关注。对巯基苯胺(PATP)由于其易吸附在大多数SERS基底表面,并可以产生极强的SERS信号,因此常被用作SERS的探针分子。二氧化钛(TiO_2)是一种目前常用的光催化剂,但是其催化效率仍有待提高。将贵金属与TiO_2复合是提高其催化效率的有效手段。本文采用电化学阳极氧化法制备了二氧化钛纳米管(TiO_2NTs),并采用光化学还原方法在表面沉积了贵金属银,制备了一种同时具有SERS和催化性能的双功能基底,即银纳米粒子修饰的二氧化钛纳米管(Ag/TiO_2NTs),研究了PATP分子在该基底上的光催化过程,并与在银镜基底上的光催化过程进行了比较。我们发现,Ag/TiO_2NTs基底上的PATP在催化过程中峰强度逐渐减弱,但没有新峰的出现;而在银镜基底上PATP的峰强度随光照时间却几乎没有变化,证明了PATP分子在Ag/TiO_2 NTs上的光催化降解过程。本文还对Ag/TiO_2NTs上PATP的催化过程进行了动力学分析,结果表明PATP在该基底表面的催化反应为一级反应。     

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。     

Facile fabrication of SERS-active substrates based on discarded silver compact disks

Surface-enhanced Raman spectroscopy (SERS) as a powerful analytical tool has gained extensive attention. Despite of many efforts in the design of SERS substrates, it still remains a grand challenge for creating a general substrate by a simple and low-cost way. Herein, we report our attempt to address this issue by fabricating SERS-active substrates based on discarded silver (Ag) compact disks (CDs). The revealed Ag layer on the CDs after removing its protective film can be used as SERS substrate directly and exhibited a good SERS activity. The Ag CDs was further roughened by electrochemical oxidation-reduction cycle in 0.1 M KCl and improved its SERS activity greatly. The effects of roughened parameters on the SERS activity were investigated in detail. Moreover, a sandwich structure consisting of Ag nanoparticles, p-aminobenzenethiol and roughened Ag CDs was fabricated as an example to further enhance the SERS activity for detection in ultra-high sensitivity. These SERS-active substrates based on Ag CDs are all low-cost and allowing a “one way use”. The fabrication is also very simple and exhibits great potential for extensive application.     

Surface-enhanced Raman scattering (SERS) activity of Ag, Au and Cu nanoclusters on TiO2-nanotubes/Ti substrate

Tubular arrays of TiO₂ nanotubes (ranging in diameter from 40 to 110 nm) on a Ti substrate were used as a support for Ag, Au or Cu deposits obtained by the sputter deposition technique, where the amount of metal varied from 0.01 to 0.2 mg/cm². Those composite supports were intended for surface-enhanced Raman scattering (SERS) investigations. Composite samples were studied with the aid of scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) to reveal their characteristic morphological and chemical features. Raman spectra of pyridine (as a probe molecule) were measured at different cathodic potentials ranging from −0.2 down to −1.2 V after the pyridine had been adsorbed on the metal-covered TiO₂ nanotube/Ti substrates. In addition, SERS spectra on a bulk standard activated Ag, Au and Cu substrates were also measured. The SERS activity of the composite samples was strongly dependent on the amount of metal deposit, e.g. at and above 0.06 mg Ag/cm², the intensity of SERS signal was even higher than that for the Ag reference substrate. The high activity of these composites is mainly a result of their specific morphology. The high SERS sensitivity on the surface morphology of the substrate made it possible to monitor very small temporal changes in the Ag metal clusters. This rearrangement was not detectable with microscopic (SEM) or microanalytical (AES) methods. The SERS activity of Au or Cu clusters was distinctly lower than those of Ag. The spectral differences exhibited by the three kinds of composites as compared to the reference metal samples are discussed.     

Improved performance of surface‐enhanced Raman scattering on silver substrates prepared in nitric acid solutions

In this work, we propose a new electrochemical method to prepare surface‐enhanced Raman scattering (SERS)‐active silver substrates in nitric acid solutions. Experimental results indicate that the SERS intensity of adsorbed Rhodamine 6G (R6G) can be significantly increased, as compared with that of R6G adsorbed on a SERS‐active Ag substrate prepared by an electrochemical method in a chloride‐containing solution, which was generally employed in the literature. Moreover, the SERS of R6G on the newly developed substrate (prepared in a nitric acid solution) still performs well at a high temperature of 250 °C. However, the enhancement capability of the SERS‐active substrate prepared in a chloride‐containing solution is seriously destroyed at temperatures higher than 150 °C. Further investigations indicate that the oxidation states of roughened Ag substrates prepared in nitric acid solutions under different experiment conditions have less influence on the corresponding SERS performances. Instead, different surface morphologies of roughened Ag substrates and different contents of nitrogen‐containing dopping ions on the roughened Ag substrates demonstrate significant effects on the corresponding SERS performances. Copyright © 2011 John Wiley & Sons, Ltd.     

银纳米颗粒阵列的表面增强拉曼散射效应研究

利用具有高密度拉曼热点的金属纳米结构作为表面增强拉曼散射(SERS)基底,可以显著增强吸附分子的拉曼信号.本文通过阳极氧化铝模板辅助电化学法沉积制备了高密度银(Ag)纳米颗粒阵列;利用扫描电子显微镜和反射谱表征了样品的结构形貌和表面等离激元特性;用1, 4-苯二硫醇(1, 4-BDT)为拉曼探针分子,研究了Ag纳米颗粒阵列的SERS效应.通过优化沉积时间,制备出高SERS探测灵敏度的Ag纳米颗粒阵列,检测极限可达10~(-13)mol/L;时域有限差分法模拟结果证实了纳米颗粒间存在强的等离激元耦合作用,且发现纳米颗粒底端的局域场增强更大.研究结果表明Ag纳米颗粒阵列可作为高效的SERS基底.     

Surface‐enhanced Raman scattering characteristics of CuO : Mn/Ag heterojunction probed by methyl orange: effect of Mn2+ doping

Interest in the synthesis of hybrid substrates for surface‐enhanced Raman scattering (SERS) has surged recently. Hereof, in the present work, a hybrid SERS substrate CuO : Mn/Ag heterojunction has been synthesised. To accomplish this, the nanostructred Ag island film and CuO : Mn nanoparticles are synthesised by vacuum thermal evaporation method and sol–gel method respectively, and thereafter, a heterojunction between the CuO : Mn and Ag is fabricated by adsorption of CuO : Mn (10^‐3 m in ethanol) on Ag island film. Further, the SERS sensitivity of CuO : Mn/Ag heterojunctions has been studied by probing methyl orange. We observed that with Mn‐doping in the lattice of CuO, the SERS signal is enhanced considerably because of ferromagnetic ordering in CuO : Mn. DFT/B3LYP/6‐311 G(d, p) method is used to calculate the energy of HOMO and LUMO level of methyl orange. Copyright © 2016 John Wiley & Sons, Ltd.     

In situ nucleation and growth of silver nanoparticles in membrane materials: a controllable roughened SERS substrate with high reproducibility

A controllable roughened silver surface with high surface‐enhanced Raman scattering (SERS) activity and high reproducibility has been developed in this study. This silver surface was prepared by silver nucleation in polyelectrolyte multilayers (PEMs) and silver‐enlarged growth. First, the small Ag nuclei were synthesized by NaBH₄ in situ reduction of Ag ions on a surface of PEMs. Then the small Ag nuclei formed were effectively enlarged by using a mixture of commercially available reagents named Li Silver . The optical properties and morphologies of the silver substrates have been investigated by ultraviolet–visible (UV–vis) spectroscopy and atomic force microscopy (AFM). The UV–vis and AFM results revealed that the small Ag nuclei separately appeared on the PEMs after NaBH₄ in situ reduction. The size of the enlarged Ag nanoparticles can be easily controlled with the immersing cycle in Li Silver. 4‐Mercaptopyridine (4‐MPY) and Rhodamine 6G (R6G) have been used as Raman probes to evaluate the properties of the new SERS substrates. It has been found that the enhancement factor of R6G reached ∼10⁹ after treatment in Li Silver. Reproducibility has been investigated using the SERS signal intensity at 1094 cm⁻¹ of 4‐MPY. Signals collected over multiple spots within the same substrate resulted in a relative standard deviation (RSD) of 6.38%, while an RSD of 10.33% was measured in signals collected from different substrates. Copyright © 2008 John Wiley & Sons, Ltd.     

1-Hexadecylamine as both reducing agent and stabilizer to synthesize Au and Ag nanoparticles and their SERS application

1-Hexadecylamine (HDA)-capped Au and Ag nanoparticles (NPs) have been successfully prepared by a one-pot solution growth method. The HDA is used as both reducing agent and stabilizer in the synthetic process is favorable for investigating the capping mechanism of Au and Ag NPs’ surface. The growth process and characterization of Au and Ag NPs are determined by Ultraviolet–visible (UV–vis) spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD). Experimental results demonstrate that the HDA-capped Au and Ag NPs are highly crystalline and have good optical properties. Furthermore, surface-enhanced Raman scattering (SERS) spectra of 2-thionaphthol are obtained on the Au and Ag NPs modified glass surface, respectively, indicating that the as-synthesized noble metal NPs have potentially high sensitive optical detection application.     

Silver‐decorated carbon nanotube networks as SERS substrates

We report on investigations upon a surface‐enhanced Raman scattering (SERS) substrate produced from a two‐dimensional single‐walled carbon nanotube (SWNT) network decorated with Ag nanoparticles. Using the strong and unique Raman spectrum of SWNTs as a reference, the SWNT/Ag nanostructure can be considered to provide two regions: one with an ultrasensitive SERS response for single‐molecule SERS (SMSERS) study; and another with uniform SERS enhancement over an area of several square millimeters for general SERS measurements. We report the appearance of an anomalous Raman feature at around 2180 cm⁻¹ in the high‐sensitivity region which exhibits the characteristics of SMSERS. The SERS performance of the uniform area was characterized using pyridine vapor adsorbed onto the substrate. The presence of the SWNT/Ag nanostructure enhanced the Raman intensity by over seven orders of magnitude, a factor comparable to or exceeding that obtained on SERS substrates reported by other groups. The results indicate great potential to produce highly sensitive, uniform SERS substrates via further fine‐tuning of the nanostructure. Copyright © 2011 John Wiley & Sons, Ltd.