Gold nanoparticles assembling on smooth silver spheres for surface-enhanced Raman spectroscopy

A simple and cost-effective chemical method was introduced to assemble gold (Au) nanoparticles on smooth silver (Ag) spheres for realizing surface-enhanced Raman scattering (SERS) enhancement by the replacement reaction between chloroauric acid and Ag spheres. In addition, the Ag-Au core-shell spheres were fabricated when a certain amount of chloroauric acid was used in the reaction solution. We found that the Ag particles decorated with small Au nanoparticles demonstrated the strongest SERS enhancement, while Ag-Au core-shell spheres showed the weakest enhancement.     

Single-molecule and single-nanoparticle SERS: from fundamental mechanisms to biomedical applications

This tutorial review discusses a new class of colloidal metal nanoparticles that is able to enhance the efficiencies of surface-enhanced Raman scattering (SERS) by as much as 10(14)-10(15) fold. This enormous enhancement allows spectroscopic detection and identification of single molecules located on the nanoparticle surface or at the junction of two particles under ambient conditions. Considerable progress has been made in understanding the enhancement mechanisms, including definitive evidence for the single-molecule origin of fluctuating SERS signals. For applications, SERS nanoparticle tags have been developed based on the use of embedded reporter molecules and a silica or polymer encapsulation layer. The SERS nanoparticle tags are capable of providing detailed spectroscopic information and are much brighter than semiconductor quantum dots in the near-infrared spectral window. These properties have raised new opportunities for multiplexed molecular diagnosis and in vivo Raman spectroscopy and imaging.     

Au@TiO2核壳纳米粒子光催化过程的表面增强拉曼光谱研究

利用聚电解质的静电吸附作用（层层组装）,在Au纳米粒子表面包裹上不同层数的二氧化钛前驱体TALH,通过退火形成Au@TiO2复合纳米粒子.以苯硫酚（TP）作为探针分子对退火前复合纳米粒子不同壳层厚度的SERS效应进行表征;可以发现：SERS信号强度的变化跟壳层厚度密切相关,当Au表面包裹至三层TALH时,信号几乎完全消失.此外,结合紫外照射,利用SERS对亚甲基蓝在TiO2壳层表面的光催化降解过程进行现场研究.结果表明：MB的降解主要经历了从多体及二聚体吸附逐渐向单体吸附方式转变,随后又经历了一个脱甲基的过程.因此,本工作发展了将一种紫外催化与现场SERS检测相结合的技术,该技术有望发展成为检测光催化过程,研究表面催化机理的一种强有力的工具     

Transition metal-coated nanoparticle films: vibrational characterization with surface-enhanced Raman scattering

The utilization of surface-attached gold nanoparticles as templates for generating Pt-group particles displaying near-optimal surface-enhanced Raman scattering (SERS) characteristics is described. Essentially epitaxial transition metal coatings down to the monolayer level can be prepared, most readily by the spontaneous replacement of an electrochemically deposited copper layer by the desired Pt-group metal. The and essentially pinhole-free nature of the coated nanoparticles is demonstrated from the form of the SER spectra for chemisorbed carbon monoxide and ethylene. The potential of the present strategy for synthesizing relatively monodispersed "core-shell" nanoparticles using a myriad of coating materials, also displaying SERS activity, is pointed out.     

Reliable Quantitative SERS Analysis Facilitated by Core–Shell Nanoparticles with Embedded Internal Standards

Quantitative analysis is a great challenge in surface‐enhanced Raman scattering (SERS). Core‐molecule‐shell nanoparticles with two components in the molecular layer, a framework molecule to form the shell, and a probe molecule as a Raman internal standard, were rationally designed for quantitative SERS analysis. The signal of the embedded Raman probe provides effective feedback to correct the fluctuation of samples and measuring conditions. Meanwhile, target molecules with different affinities can be adsorbed onto the shell. The quantitative analysis of target molecules over a large concentration range has been demonstrated with a linear response of the relative SERS intensity versus the surface coverage, which has not been achieved by conventional SERS methods.     

Wide range temperature detection with hybrid nanoparticles traced by surface-enhanced Raman scattering

We report on the fabrication of a class of surface-enhanced Raman scattering(SERS)active thermometers,which consists of60 nm gold nanoparticles,encoded with Raman-active dyes,and a layer of thermoresponsive poly(N-isopropylacrylamide)(PNIPAM)brush with different chain lengths.These SERS-active nanoparticles can be optimized to maintain spectrally silent when staying as single particles in dispersion.Increasing temperature in a wide range from 25 to 55°C can reversibly induce the interparticle self-aggregation and turn on the SERS fingerprint signals with up to 58-fold of enhancement by taking advantage of the interparticle plasmonic coupling generated in the process of thermo-induced nanoparticles self-aggregation.Moreover,the most significative point is that these SERS probes could maintain their response to temperature and present all fingerprint signals in the presence of a colored complex.However,the UV-Vis spectra can distinguish the differences faintly and the solution color shows little change in such complex mixture.This proof-of-concept and Raman technique applied here allow for dynamic SERS platform for onsite temperature detection in a wide temperature range and offer unique advantages over other detection schemes.     

Magnetism and application of NiFe@Au nanoparticles

This report describes the synthesis of magnetic NiFe@Au (i.e., NiFe core with Au shell) nanoparticles as functional spectroscopic probes. Both of the magnetic NiFe nanoparticles and its composite NiFe@Au particles were synthesized in aqueous solution. It is more analogous with the biological organism environment. The composite nanoparticles were dispersible in aqueous solution and could be directed by a magnetic field. Such NiFe@Au nanoparticles have been shown to function as magnetic and spectroscopic nanoprobes for surface enhanced Raman scattering (SERS) detection of molecules attached to the surface of the nanoparticles. It shows more potential functional SERS nanoprobes for biomolecular separation and detection.     

pH值和阴离子对吡啶2,6-二羧酸在金纳米颗粒表面的增强拉曼散射的影响

表面增强拉曼散射(SERS)被用于检测细菌芽孢中的一种重要的标志物吡啶2,6-二羧酸(DPA)。以聚乙烯吡咯烷酮(PVP)为粘合剂,将60 nm的金粒子组装到表面打磨光滑的金电极上,制备稳定、灵敏的SERS基底。通过不同pH值下吸附在金基底上的DPA的SERS特征,考察DPA分子吸附构型发生的变化,并分析酸根离子对其吸附的影响。结果表明:在强酸条件下,DPA在Au NPs/PVP/Au基底上的SERS信号能达到最大增强;当pH值大于DPA二级解离常数时,DPA的SERS特征逐渐减弱。在DPA中引入不同酸根盐时,后者会取代纳米金表面的柠檬酸根所占的部分位点,改变Au NPs-Au基底的SERS增强性能。3种酸根吸附性能不同,所以获得的光谱强度存在差异。     

p-Benzosemiquinone radical anion on silver nanoparticles in water

This communication reports the SERS observation of p-benzosemiquinone radical anion, produced on reduction of p-benzoquinone by Ag nanoparticles at the metal-water interface. The species is positively identified by comparison of the SERS spectrum with the resonance Raman spectra of the radical anion in aqueous solution. This is a rare SERS observation of a radical intermediate formed by surface reaction on nanosize silver particles in solution.     

Surface-enhanced raman spectra of dyes and organic acids in silver solutions: chloride ion effect

We have recorded surface-enhanced Raman (SER) spectra of two different classes of compounds, cationic dyes and organic acids, and studied their chloride ion effects on the surface-enhanced Raman scattering (SERS) activities of the silver solution. For the positive charge dyes, rhodamine 6G (R6G) and 1,1'-dimethyl-2,2'-cyanine iodide (DECI), no SERS could be observed without the addition of chloride ions because of lack of the electrostatic interaction between the dye species and the silver particles in the silver solution. The chloride ions served to enlarge silver particles and to contribute the existence of the surface active sites, making the silver solution SERS active to the dye samples. Surface-enhanced resonance Raman scattering (SERRS) intensity of the dye molecules increased with the chloride ion concentration. After reaching a maximum intensity, a Cl- quenching effect on the intensity took place. For the organic acids, benzoic acid and p-aminobenzoic acid (PABA), SERS could be observed without the coexistence of chloride ions. The intensity of the Raman scattering did not vary significantly in the presence of small amount of chloride ion. At high Cl- concentration, quenching SERS intensity began to take effect.     

双金属双硅层核-壳纳米结构Au@SiO2@Ag@SiO2用于葡萄糖检测

制备了一种灵敏度高、 稳定性强的双金属双硅层核-壳结构纳米材料Au@SiO₂@Ag@SiO₂. 由于双金属之间的硅层促进了远程等离子体的激发转移, 使该纳米粒子具有良好的表面增强拉曼散射(SERS)的特性及优异的稳定性. 利用这种SERS活性材料能直接检测出人体尿液的主要成分, 且该材料呈现出对低浓度(10^-6 mol/L)葡萄糖的无标记高效检出能力. 此外, 还实现了人工尿液中等浓度(10^-3 mol/L)葡萄糖和尿素分子的同时检测, 以及实际尿液中10^-3 mol/L葡萄糖的检测. Au@SiO₂@Ag@SiO₂纳米粒子具有在多种生物分子存在时快速检测葡萄糖的实际应用潜力.     

A controlled and reproducible pathway to dye-tagged, encapsulated silver nanoparticles as substrates for SERS multiplexing

Silver nanoparticles tagged with dyes and encapsulated within a silica layer, offer a convenient potential substrate for performing multiplexed surface-enhanced Raman scattering (SERS) analysis. In contrast to our earlier work with gold particles, aggregation of silver particles is found to be mostly independent of dye addition, allowing for a reproducible preparation in which aggregation is actively induced by the addition of NaCl. Separating the aggregation step eliminates competitive binding between the dyes and silica-coating reagents, enabling the efficient use of a wide variety of weakly binding dyes to conveniently generate robust, high-intensity SERS substrates at a variety of excitation frequencies.     

Selective surface-enhanced fluorescence and dye aggregation with layer-by-layer film substrates

One of the avenues for the development of the analytical applications of surface enhanced spectroscopy is the engineering of enhancing substrates that would be selective and target specific. In the present report, the proof of this concept is demonstrated using the layer-by-layer (LbL) technique to fabricate portable selective substrates containing metal nanoparticles which can provide surface enhanced fluorescence (SEF) or surface enhanced Raman scattering (SERS). The selectivity to ionic species is attained by adding metal-free top layers of polymer electrolytes to an LbL SERS enhancing substrate. In addition, it was observed that the surface charge of the top layer determines the dye aggregation, leading to the formation of adsorbed J or H aggregates.     

SERS and FDTD simulation of gold nanoparticles grafted on germanium wafer via galvanic displacement

Uniform and dense Au nanoparticles grown on Ge (Au/Ge) were fabricated by a facile galvanic displacement method and employed as surface‐enhanced Raman scattering (SERS) substrates. The substrates exhibited excellent reproducibility in the detection of rhodamine 6G aqueous solution with a relative standard deviation of <20%. The substrate showed a high Raman enhancement factor of 3.44 × 10⁶. This superior SERS sensitivity was numerical confirmed by the three‐dimensional finite‐difference time‐domain method, which demonstrated a stronger electric field intensity (|E/E₀|²) distribution around the Au nanoparticles grown on Ge. This facile and low‐cost prepared Au/Ge substrate with high SERS sensitivity and reproducibility might have potential applications in monitoring in situ reaction in aqueous solution. Copyright © 2014 John Wiley & Sons, Ltd.     

Photochemical decoration of silver nanoparticles on magnetic microspheres as substrates for the detection of adenine by surface-enhanced Raman scattering

In this work, silver nanoparticles (AgNPs) decorated magnetic microspheres (MMs) are prepared as surface-enhanced Raman scattering (SERS) substrate for the analysis of adenine in aqueous solutions. To prepare these substrates, magnetic particles were first synthesized by coprecipitation of Fe(II) and Fe(III) with ammonium hydroxide. A thin layer of cross-linked polymer was formed on these magnetic particles by polymerization through suspension of magnetic particles into a solution of divinyl benzene/methyl methacrylate. The resulted polymer protected magnetic particles are round in shape with a size of 80 μm in diameter. To form AgNPs on these MMs, photochemical reduction method was employed and the factors in photochemical reduction method were studied and optimized for the preparation of highly sensitive and stable AgNPs on MMs substrates (abbreviated as AgMMs substrates). By dispersing the AgMMs in aqueous samples, cylindrical magnet was used to attract the AgMMs for SERS detections. The observed enhancement factor of AgMMs reached 7 orders in magnitude for detection of adenine with a detection limit approaching to few hundreds of nanomolar.     

基于金纳米聚集体的核壳型SERS探针及其细胞内应用

利用金纳米粒子的聚集体作为表面增强拉曼散射（Surface enhanced Raman scattering,SERS）的增强基底,合成了一种二氧化硅包裹的核壳型SERS探针,并成功将该探针应用于活细胞的SERS光谱探测.实验中利用4-巯基苯甲酸（4-mercaptobenzoicacid,4MBA）作为拉曼标记物,...     

复合SERS基底的构建及性质

通过自组装方法以对巯基苯胺(PATP)为偶联分子, 在石英基片上构筑了多种形貌的银钠米粒子单层结构和三明治结构. 研究了组装膜在不同激发线下表面增强拉曼散射(SERS)的增强差异. 研究结果表明, 单层基底和三明治基底中偶联分子的SERS信号因银纳米粒子间的电磁场耦合而显著增强, 且在三明治结构中增强更加明显. 对复合SERS基底增强因子进行计算可知, 复合SERS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. 在三明治结构中更易发生PATP分子转变为对巯基偶氮苯(DMAB)分子的激光诱导催化偶联反应. 另外, 该激光诱导催化偶联反应与激发波长密切相关.     

SERS from molecules adsorbed on small Ag nanoparticles: A microscopic model

A microscopic approach to surface-enhanced Raman scattering (SERS) from molecules adsorbed on noble-metal nanoparticles is developed. For nanoparticle sizes smaller than 10 nm, the classical electromagnetic enhancement mechanism is modified by quantum-size effects. Using time-dependent local field approximation, we perform systematic analysis of SERS in nanometer-sized Ag nanoparticles. We find that, in small nanoparticles, Raman cross-section enhancement is governed by the interplay between Landau damping of the surface plasmon and interband screening in the nanoparticle surface layer.     

A highly sensitive detection platform based on surface-enhanced Raman scattering for Escherichia coli enumeration

A very sensitive and highly specific heterogeneous immunoassay system, based on surface-enhanced Raman scattering (SERS) and gold nanoparticles, was developed for the detection of bacteria and other pathogens. Two different types of gold nanoparticles (citrate-stabilized gold nanosphere and hexadecyltrimethylammonium bromide (CTAB)-stabilized gold nanorod particles) were examined and this immunoassay was applied for the detection of Escherichia coli. Raman labels were constructed by using these spherical and rod-shaped gold nanoparticles which were first coated with 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB) and subsequently with a molecular recognizer. The working curve was obtained by plotting the intensity of the SERS signal of the symmetric NO₂ stretching of DTNB at 1,333 cm⁻¹ versus the concentration of the E. coli. The analytical performance of gold particles was evaluated via a sandwich immunoassay, and linear calibration graphs were obtained in the E. coli concentration range of 10¹–10⁵ cfu/mL with a 60-s accumulation time. The sensitivity of the Raman label fabricated with gold nanorods was more than three times higher than spherical gold nanoparticles. The selectivity of the developed sensor was examined with Enterobacter aerogenes and Enterobacter dissolvens, which did not produce any significant response. The usefulness of the developed immunoassay to detect E. coli in real water samples was also demonstrated.     

利用去湿现象制备具有SERS活性的银纳米粒子图案

构建了具有表面增强拉曼散射(SERS)活性的二维有序环状与盘状的银纳米粒子结构, 利用CTAB包覆银纳米粒子的氯仿溶液直接在图案化的金基底上进行去湿, 当改变银纳米粒子的浓度时可以得到不同的图案. 利用原子力显微镜(AFM)对其结构进行了表征, 以4-巯基吡啶作为探针分子, 采用表面增强拉曼成像技术研究了这种基底的SERS活性, 这将为SERS的研究开拓新的领域.