Temperature dependence of silver nanostructure for surface enhanced Raman scattering application

We study the fabrication and application of the fractal silver nanostructure using an electrochemical process. Scanning electron microscope and high resolution transmission electron microscope images show the morphology of silver nanostructure can be well controlled via the various reaction times. The surface enhanced Raman scattering of 10 microM aqueous Rhodamine 6G (R6G) solutions conducted in as-fabricated silver nanostructure achieved an enhancement factor approximately 10(5) at room temperature. Meanwhile, an approximately 10(4) enhancement factor of SERS signal can be kept under 200 degrees C in present study. This study can help us to integrate the nano-metals and nano-particles for advanced nano devices.     

Superhydrophobicity and surface enhanced Raman scattering activity of dendritic silver layers

Dendritic silver nanostructured surface has been prepared on copper substrate by a simple replacement reaction. It was observed that morphology of the silver surface became much rough with reaction time, from initial nanosized clusters to nanostructured dendrites. The silver surface modified with dodecanethiol showed great superhydrophobicity. It was also found that the dendritic silver nanostructured surface demonstrated highly sensitive surface enhanced Raman scattering (SERS) character. It is expected that the dendritic silver surface may be applied as molecular probe and biological sensing.     

A convenient approach to synthesize silver nanoshell covered functionalized polystyrene beads: A substrate for surface enhanced Raman scattering

The synthesis of ultra-thin silver nanoshell on anionic polystyrene bead has been reported from specific silver precursor [Ag(NH₃)₂]⁺ primarily through ion exchange mechanism. The particles were characterized by SEM, EDX, XPS and XRD analysis. Finally, the particles were exploited as a solid substrate for surface enhanced Raman scattering study using crystal violet as a Raman probe.     

Active control of silver nanoparticles spacing using dielectrophoresis for surface-enhanced Raman scattering

We demonstrate an active microfluidic platform that integrates dielectrophoresis for the control of silver nanoparticles spacing, as they flow in a liquid channel. By careful control of the nanoparticles spacing, we can effectively increase the surface-enhanced Raman scattering (SERS) signal intensity based on augmenting the number of SERS-active hot-spots, while avoiding irreversible aggregation of the particles. The system is benchmarked using dipicolinate (2,6-pyridinedicarboxylic acid) (DPA), which is a biomarker of Bacillus anthracis. The validity of the results is discussed using several complementing characterization scenarios.     

Plasmonic dimer antennas for surface enhanced Raman scattering

Electron beam induced deposition (EBID) has recently been developed into a method to directly write optically active three-dimensional nanostructures. For this purpose a metal-organic precursor gas (here dimethyl-gold(III)-acetylacetonate) is introduced into the vacuum chamber of a scanning electron microscope where it is cracked by the focused electron beam. Upon cracking the aforementioned precursor gas, 3D deposits are realized, consisting of gold nanocrystals embedded in a carbonaceous matrix. The carbon content in the deposits hinders direct plasmonic applications. However, it is possible to activate the deposited nanostructures for plasmonics by coating the EBID structures with a continuous silver layer of a few nanometers thickness. Within this silver layer collective motions of the free electron gas can be excited. In this way, EBID structures with their intriguing precision at the nanoscale have been arranged in arrays of free-standing dimer antenna structures with nanometer sized gaps between the antennas that face each other with an angle of 90°. These dimer antenna ensembles can constitute a reproducibly manufacturable substrate for exploiting the surface enhanced Raman effect (SERS). The achieved SERS enhancement factors are of the order of 10? for the incident laser light polarized along the dimer axes. To prove the signal enhancement in a Raman experiment we used the dye methyl violet as a robust test molecule. In future applications the thickness of such a silver layer on the dimer antennas can easily be varied for tuning the plasmonic resonances of the SERS substrate to match the resonance structure of the analytes to be detected.     

Convective assembly of linear gold nanoparticle arrays at the micron scale for surface enhanced Raman scattering

A convective assembly technique at the micron scale analogous to the writing action of a “pipette pen” has been developed for the linear assembly of gold nanoparticle strips with micron scale width and millimeter scale length for surface enhanced Raman scattering (SERS). The arrays with interparticle gaps smaller than 3 nm are hexagonally stacked in the vicinity of the pipette tip. Variable numbers of stacked layers and clean surfaces of the assembled nanoparticles are obtained by optimizing the velocity of the pipette tip. The SERS properties of the assembled nanoparticle arrays rely on their stacking number and surface cleanliness.      

Metal-coated magnetic nanoparticles for surface enhanced Raman scattering studies

We report the optimization and usage of surfactantless, water dispersible Ag and Au-coated gboldsymbolgamma–Fe₂_{boldsymbol 2}O₃_{boldsymbol 3} nanoparticles for applications in surface-enhanced Raman scattering (SERS). These nanoparticles, with plasmonic as well as super paramagnetic properties exhibit Raman enhancement factors of the order of 10⁶ (10⁵) for Ag (Au) coating, which are on par with the conventional Ag and Au nanoparticles. Raman markers like 2-naphthalenethiol, rhodamine-B and rhodamine-6G have been adsorbed to these nanoparticles and tested for nonresonant SERS at low concentrations. Further, to confirm the robustness of Ag-coated nanoparticles, we have performed temperature-dependent SERS in the temperature range of 77–473 K. The adsorbed molecules exhibit stable SERS spectra except at temperatures $boldsymbol >$boldsymbol >323 K, where the thermal desorption of test molecule (naphthalenethiol) were evident. The magnetic properties of these nanoparticles combined with SERS provide a wide range of applications.     

A silver nanoparticle thin film modified glass substrate as a colourimetric sensor for hydrogen peroxide

In this work, a silver nanoparticle (AgNP) coated glass slide was developed as a device for sensing hydrogen peroxide. AgNPs were synthesised using borohydride reduction with a citrate stabiliser, resulting in a negatively charged stabilised particle surface. The particles were attached to the glass surface using the layer-by-layer (LbL) technique. Poly (diallyldimethylammonium chloride) and poly (styrene sulphonate) were used as cationic and anionic polyelectrolyte layers, respectively. The glass slide was modified with polyelectrolytes leaving a cationic layer on the top surface. The AgNPs were subsequently deposited on the slide via electrostatic interaction. As a result, a dark yellow film of AgNPs was obtained with maximum absorption at 410 nm. Film fabrication based on LbL assembly provided acceptable reproducibility (relative standard deviation = 6.5%). The fabricated film had long-term stability (>6 weeks). A very small quantity of AgNPs was used in this method. Fabrication was performed under ambient conditions. Therefore this fabrication was considered as a green method. The AgNP modified slide was developed to sense hydrogen peroxide. Detection is based upon oxidation of AgNPs by hydrogen peroxide. This results in a change in colour of the film from dark yellow to colourless. Linear calibration was obtained over the range of 1.0--100.0 mM of hydrogen peroxide. The device was successfully used for measuring hydrogen peroxide in urine.     

Butterfly-wing hierarchical metallic glassy nanostructure for surface enhanced Raman scattering

Nano Research - The surface-enhanced Raman spectroscopy (SERS) is a technique for the detection of analytes on the surface with an ultrahigh sensitivity down to the atomic-scale, yet the...     

Differentiation of bacteria cell wall using Raman scattering enhanced by nanoparticle array

We have fabricated surface-enhanced Raman scattering (SERS) substrates based on arrays of silver nanoparticles grown on porous anodic alumina templates. Using this nanotechnology platform, label-free and high-speed detection of bacteria are achieved. SERS spectra of various bacteria including Staphylococcus Aureus (Gram-positive bacterium), Klebsiella Pneumoniae (Gram-negative bacterium), and Mycobacterium Smegmatis (Mycobacterium) were recorded. The highly reproducible SERS-based technological platform is capable of differentiating different kinds of bacteria by PCA, LDA, clustering analysis, and SVM methods, which provides promising opportunity for biosensing of clinical microbes.     

Separation free DNA detection using surface enhanced Raman scattering

Surface enhanced raman scattering (SERS) based molecular diagnostic assays for the detection of specific DNA sequences have been developed in recent years to compete with the more common fluorescence based approaches. Current SERS assays either require time-consuming separation steps that increase assay cost and can also increase the risk of contamination or they are negative assays, where the signal intensity decreases in the presence of target DNA. Herein, we report a new separation free SERS assay with an increase in signal intensity when target DNA is present using a specifically designed SERS primer. The presence of specific bacterial DNA from Staphylococcus epidermidis was detected using polymerase chain reaction (PCR) and SERS and indicates a new opportunity for exploration of SERS assays requiring minimal handling steps.     

Imaging surface plasmon of gold nanoparticle arrays by far-field Raman scattering

We present Raman spectra and Raman images of the methylene blue molecule adsorbed as a single layer on gold nanoparticles regularly arranged in periodic arrays. Spectra and images are recorded in the same spatial and spectral regions using an excitation under total internal reflection. Images of the Raman scattering appear as spots of circular shape located at the particle positions with size defined by the diffraction limit. It appears that all excited particles contribute equally to the Raman signal if the Gaussian intensity distribution of the laser beam is taken into account. These results demonstrate that Raman scattering can be a useful technique to study plasmon properties.     

柔性可擦拭表面增强拉曼散射基底的原位制备和应用

为了检测水果表面农药残留,通过化学沉积-原位生长法制备Ag/棉签柔性可擦拭表面增强拉曼光谱（SERS）基底。通过调控生长介质中硝酸银的浓度,得到了银纳米粒子紧密堆积的Ag/棉签复合材料。通过扫描电子显微镜、透射电子显微镜、红外光谱仪、热重分析仪对Ag/棉签复合材料的形貌、结构及其性能进行表征。利用尼尔兰作为探针分子表征了Ag/棉签复合材料的SERS性能,实现了对水果表面农药残留福美双的快速检测。结果表明,银纳米粒子直径分布在50～70 nm之间。Ag/棉签复合材料表现出优异的光谱均一性,相对标准偏差为3.72%。对尼尔兰的检出限低于10^-7 mol/L。通过简单的擦拭直接检测梨不规则表面上的福美双农药残留,检出限达到10^-6 mol/L。该制备方法可以简单地扩展到其他纤维素化合物,例如吸棉花和纸等。本研究提出了一种简单快速的方法用于制备廉价、环保的柔性SERS基底。     

Silver-doped sol-gel film as a surface-enhanced Raman scattering substrate for detection of uranyl and neptunyl ions

A surface-enhanced Raman scattering (SERS) substrate containing silver particles was prepared by an acid-catalyzed sol-gel method. Silver nitrate was first doped into the sol-gel film followed by chemical reduction of the silver ions with sodium borohydride to produce silver particles. This silver-doped sol-gel substrate exhibits strong enhancement of Raman scattering from adsorbed uranyl ions with a detection limit of 8.5 x 10(-8) M, which is comparable to existing methods of uranyl detection such as spectrophotometry, fluorometry, and a SERS method based on ligand-modified solution silver colloids. However, in the present method, no preconcentration steps, chromogens, or complexing ligands are needed. Compared with the SERS method using Ag colloidal sols, the silver-doped sol-gel film has the advantage that the silver particles trapped in the sol-gel matrix are much more stable than Ag colloids in liquid media. Furthermore, porous silica sol-gel materials are known to have affinities toward many inorganic and organic molecules. The enhanced adsorption affinities could also lead to the increased SERS sensitivity. The performance of the new silver-doped sol-gel substrate was evaluated with uranyl ions and compared to that of a SERS substrate based on silver-coated silica beads prepared by vacuum deposition. The detection limit for the silver-doped sol-gel film was 104 times lower than that for the silver-coated silica beads. The sol-gel substrate was further used to obtain, for the first time, the surface-enhanced Raman spectrum of neptunyl ions in dilute aqueous solutions.     

Surface enhanced Raman scattering of silver sensitized cobalt nanoparticles in metal-dielectric nanocomposites

We report the preparation of a new type of nanocomposite containing cobalt and silver nanoparticles organized in parallel layers with a well controlled separation. This arrangement allows the observation of an enhanced low-frequency Raman signal at the vibration frequency of cobalt nanoparticles excited through the surface plasmons of silver nanoparticles. Numerical simulations of the electric field confirm the emergence of hot spots when the separation between silver and cobalt nanoparticles is small enough.     

Quantitative enhanced Raman scattering of labeled DNA from gold and silver nanoparticles

Surface-enhanced resonance Raman scattering (SERRS) from silver nanoparticles using 514.5-nm excitation has been shown to offer huge potential for applications in highly sensitive multiplexed DNA assays. If the technique is to be applied to real biological samples and integrated with other methods, then the use of gold nanoparticles and longer wavelengths of excitation are desirable. The data presented here demonstrate that dye-labeled oligonucleotide sequences can be directly detected by SERRS using gold nanoparticles in a quantitative manner for the first time. The performance of gold and silver nanoparticles as SERRS substrates was assessed using 514.5-, 632.8-, and 785-nm excitation and a range of 13 commercially available dye-labeled oligonucleotides. The quantitative response allowed the limit of detection to be determined for each case and demonstrates that the technique is highly effective, sensitive, and versatile. The possibility of excitation at multiple wavelengths further enhances the multiplexing potential of the technique. The importance of effectively combining the optical properties of the nanoparticle and the dye label is demonstrated. For example, at 632.8-nm excitation, the dye BODIPY TR-X and gold nanoparticles make a strong SERRS combination with very little background fluorescence. This study allows the choice of nanoparticle and dye label for particular experimental setups, and significantly expands the applicability of enhanced Raman scattering for use in many disciplines.     

Fabrication of gold nanoparticle modified ITO substrate to detect beta-amyloid using surface-enhanced Raman scattering

Alzheimer's disease is a progressive neurodegenerative disorder that is characterized by the deposition of beta-amyloid (Abeta) peptide and the formation of neurofibrillary tangles in neurons. The Abeta peptide is a key molecule in the pathogenesis of Alzheimer's disease and an important marker for early diagnosis. Surface-enhanced Raman scattering (SERS) has recently been attracting keen interest in various fields such as for biosensors or immunoassays. In this study, gold nanoparticles (Au NPs) were electrochemically deposited on an indium tin oxide (ITO) substrate at different heights. Abeta antibodies were immobilized on the Au-NP-coated ITO substrate, after which the interactions between the antigen and the antibody were determined via SERS spectroscopy. The SERS responses were strongest at the Au NP array height of 91 nm, with a good linear relationship that corresponded to the change in the concentration of the antigen. This Au-NP-array-mediated SERS can be applied with a highly sensitive immunodetection biosensor.     

A reusable surface-enhanced Raman scattering (SERS) substrate prepared by atomic layer deposition of alumina on a multi-layer gold and silver film

A thermally stable, reusable surface-enhanced Raman scattering (SERS) substrate consisting of a gold/silver bi-layer film with a protective alumina coating is reported. The film is synthesized by thermally evaporating sequential layers of gold and silver followed by coating an ultra-thin alumina layer using atomic layer deposition. The use of gold as the foundational layer improves the thermal stability of the metal bi-layer film while providing the additional ability to tune the SERS response. Deposition of the thin alumina overlayer on the bi-layer film creates a SERS substrate capable of enduring multiple high-temperature exposures to 400 °C with minimal loss of enhancement capabilities. We demonstrate the multi-use capability of the substrate by measuring the SERS spectrum of rhodamine 6G followed by a thermal treatment at 400 °C to remove the analyte. A representative substrate was used to acquire SERS spectra of rhodamine 6G up to five repeat measurements, thus establishing the reusability of this relatively simple, inexpensive, and stable substrate.     

Ag nanoparticles coated SWCNT with surface enhanced Raman scattering (SERS) signals

We report here a simple method to fabricate the silver nanoparticles (AgNPs) coated DNA-SWCNTs that give SERS signals. Dynamic light scattering (DLS), atomic force microscopy (AFM), and high resolution transmission electron microscopy (HRTEM) suggested the products are dispersive and soluble in aqueous solution. The Raman scattering spectra show AgNPs coated SWCNTs have enhanced the Raman signal when compared with pure SWCNT. From the radial breathing mode (RBM) of the Raman spectra, we can disclose that this DNA-SWCNT has unique chirality, which implies that it could be a good nanoprobe for cell marking.