Surface-enhanced Raman Scattering Applications Research Articles

Green Synthesis of Ag Thin Films on Glass Substrates and Their Application in Surface-Enhanced Raman Scattering

Nanostructured Ag thin films could be facilely prepared by soaking glass substrates in ethanolic solutions containing <TEX>$Ag_2O$</TEX> powders at an elevated temperature. The formation of zero-valent Ag was corroborated using X-ray diffraction and X-ray photoelectron spectroscopy. The deposition of Ag onto a glass substrate was readily controlled simply by changing the reaction time. Due to the aggregated structures of Ag, the surface-enhanced Raman scattering spectra of benzenethiol could be clearly identified using the Ag-coated glass. The enhancement factor at 514.5 nm excitation estimated using benzenethiol reached <TEX>$1.0{\times}10^5$</TEX> while the detection limit of rhodamine 6G was found to be as low as <TEX>$1.0{\times}10^{-13}$</TEX> M. Since this one-pot fabrication method is eco-friendly and is suitable for the mass production of diverse Ag films, it is expected to play a significant role in the development of surface plasmon-based analytical devices.

Rapid Synthesis of Silver Nanowires and Network Structures under Cuprous Oxide Nanospheres and Application in Surface-Enhanced Raman Scattering

Crystalline silver nanowires, with diameters of 50–500 nm and lengths up to tens of micrometers, have been successfully synthesized by a simple wet chemical route by using cuprous oxide nanospheres as a reductant and directional agent. The products are characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and UV–vis absorption spectroscopy. The two-dimensional netlike nanostructure is composed of several silver nanowires. The possible mechanism for the formation of silver nanowires is discussed. It is found that the architecture of silver crystals is drastically influenced by the concentration of the precursors and the reaction temperature. The experimental results reveal that the Cu2O nanospheres might play the two roles during the growth process of silver nanowires. Except for a reducing agent, Cu2O nanospheres act as a growth substrate to induce the formation of silver nanowires and a two-dimensional netlike nanostructure. Furthermore, the obtained two-dimensional netlike silver nanostructure can be used as surface-enhanced Raman scattering (SERS) substrates with high SERS activity and stability for detecting Rhodamine 6G (R6G) molecules. The analytical enhancement factor on the two-dimensional netlike silver nanostructure substrate is about 8 × 1010. Compared with other morphologies of silver substrates, it is found that the two-dimensional netlike silver nanowires exhibit the highest SERS sensitivity. Hence, SERS substrates of the two-dimensional netlike silver nanowires described in this work have potential applications in chemical and biological analysis as well as medical detection.

One-step Synthesis of Shape-controllable Gold Nanoparticles and Their Application in Surface-enhanced Raman Scattering

Gold nanoparticles (NPs) of various shapes were synthesized by a one-step method at ambient temperature in the presence of NaCl. 2-mercaptosuccinic acid (MSA) was used as both reducing agent and stabilizing agent. The shapes of gold NPs were controllable by simply tuning S/Au ratio (S is from MSA molecule, and S/Au ratio is controlled by tuning the volume of added MSA solution), and triangle, polygonal and spherical nanoparticles were obtained. This result suggested a new way to consider the effects of MSA on the growth of nanoparticles, which showed that MSA is a strong capping agent and facilitates more uniform growth of nanoparticles in every dimension. And other important factors on nanoparticles growth including NaCl and temperature were discussed. Furthermore, a typical probe molecule, 4-aminothiophenol (4-ATP) was used to test the surface-enhanced Raman scattering (SERS) activity of these gold NPs and the results indicated good Raman activity on these substrates. And the enhancement factor (EF) at 1078 cm−1 (a1) was estimated to be as large as 6.3 × 104 and 5.5 × 104 for triangular plates and truncated particles, respectively.

Fabrication of Metal Half-Shells Using Colloidal Particle Monolayer and Their Application in Surface-Enhanced Raman Scattering

Three types of Au shells, an isolated half-shell, one-dimensional strings of shells, and two-dimensional films, were fabricated by using a monolayer of polystyrene (PS) particles with diameters of 213, 560, and 1360 nm. The three types of Au shells that were removed from the PS particle monolayer and the as-deposited Au shells that adhered to PS particles were modified with 4-mercaptopyridine for use as platforms for surface-enhanced Raman scattering (SERS). We examined the effects of the shapes and sizes of Au shells on their SERS efficiency and found that the Au shells exhibited strong SERS signals and that Au shells prepared by using 560-nm PS particles were the most suitable platform for SERS at both 632.8- and 785-nm excitations. Further, we found that SERS enhancements depended on the shape of Au shells and on whether Au shells adhered to PS particles or not.

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.

Controllable Synthesis of Water-Soluble Gold Nanoparticles and Their Applications in Electrocatalysis and Surface-Enhanced Raman Scattering

We report a facile method to synthesize water-soluble gold nanoparticles (AuNPs) using a biosurfactant sodium cholate as reducing reagents and protective groups in aqueous solution at ambient temperature. The diameters (13-70 nm) of uniform AuNPs can be readily adjusted by changing the initial molar ratio of sodium cholate to chloroauric acid (HAuCl(4)). Also, the alkaline condition of preparative solution is found to affect the size of as-synthesized AuNPs. This synthetic approach is one-step and "green". The obtained AuNPs exhibit a good electrocatalytic activity toward methanol oxidation. Meanwhile, the AuNPs thin films can serve as an efficient substrate for surface-enhanced Raman scattering (SERS). Furthermore, platinum nanoparticles (PtNPs) are also prepared by reducing sodium tetrachloro platinate hydrate with sodium cholate.

Monodispersed Protein Stabilized Silver Nanoprisms: Synthesis, Optical Properties and Surface-Enhanced Raman Scattering Application

Protein stabilized, water soluble silver nanoparticles are essential for biomedicine and biotechnology. The abundant protein such as gelatin and bovine serum albumin (BSA) has a remarkable ability of binding and transporting materials across cell membrane that makes it ideal for drug delivery and very useful for pharmaceutical industry. In this article, silver nanoprisms were synthesized by reacting an aqueous solution of silver nitrate with proteins such as gelatin and bovine serum albumin at different conditions, where proteins provided the dual function of Ag (I) reduction and Ag(0) prism-like structures formation. The solution exhibited an excellent colloidal stability by the visible observation. UV-vis spectra and transmission electron microscopy (TEM), revealed the formation of well-dispersed Ag nanoprisms with different sizes. Furthermore, the fluorescence intensity of proteins was drastically quenched in presence of Ag nanoprisms from the results of fluorescence spectra. The surface enhanced Raman scattering spectrum of anisotropic silver nanoprisms was also presented.

Fabrication of Rice-Like Gold Nanoparticles and Application in Surface-Enhanced Raman Scattering

A simple method for the synthesis of rice-like gold nanoparticles using gold nanorods (GNRs) as precursors in the aqueous phase was exploited. The method used in this work involves eroding GNRs with potassium ferricyanide in the aqueous phase. Surface plasmon resonance (SPR) bands of the resulting nanoparticles present a notable blue-shift from 670 to 570 nm with increasing amounts of potassium ferricyanide, and subsequently the shape of the resulting nanoparticles can be readily controlled. Most importantly, the SPR response is an almost linear function of the quantity of potassium ferricyanide added. The synthesis of the resulting nanoparticles with various aspect ratios has been extensively studied and is well established. The surface-enhanced Raman scattering (SERS) intensity enhancement of the adsorbate on the surface of these gold nanoparticles was also studied.

Preparation and optical properties of silver nanowires and silver-nanowire thin films

Silver nanowires and silver-nanowire thin films have attracted much attention due to their extensive applications in Surface-Enhanced Raman Scattering (SERS) and Surface-Enhanced Fluorescence (SEF). Thin films of silver nanowires within polyelectrolyte layers of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS) were fabricated by the Spin-Assisted Layer-by-Layer (SA-LbL) method. The surface coverage, thickness, and absorbance properties of the silver-nanowire films were controlled by the number of layers deposited. Both transverse and longitudinal surface plasmon (SP) modes of the silver-nanowires were observed in the absorbance spectra, as was evidence for nanowire interaction. Two-dimensional finite difference time-domain (2D FDTD) simulations predict that the maximum field enhancement occurs at the ends and cross-sectional edges of the wires for the longitudinal and transverse modes, respectively. Silver nanowires were synthesized by a facile, high-yield solvothermal approach, which can be easily manipulated to control the aspect ratio of the nanowires. The effects of polyvinylpyrrolidone (PVP) concentration and molecular weight on the growth of the silver nanowires, which are not documented in the original procedure, are discussed. It is shown that the growth mechanism for silver nanowires in the solvothermal synthesis is similar to that reported for the polyol synthesis.

Br−-Induced Facile Fabrication of Spongelike Gold/Amino Acid Nanocomposites and Their Applications in Surface-Enhanced Raman Scattering

We report a facile method for the fabrication of spongelike gold/amino acid nanocomposites by the addition of NaBr to glutamic acid-stabilized gold nanoparticles (GNPs) at room temperature. The gold/glutamic acid (Glu) nanocomposite is characterized by TEM, SEM, UV-vis spectroscopy, and XRD measurements. The results suggest that the three-dimensional spongelike gold/Glu nanocomposites with mean diameter of 50 nm are formed via the nanospheres fusing into one another. The driving force for the fabrication of spongelike gold/amino acid nanocomposites is the van der Waals attractive forces of Br(-) partially coated GNPs. Furthermore, the obtained spongelike gold nanocomposites can be used as surface-enhanced Raman scattering (SERS) substrates with high SERS activity and stability for detecting Rhodamine 6G (R6G) molecules. Hence, NaBr-mediated preparation of SERS substrates described in this work has potential applications in chemical and biological analysis as well as medical detection.

Preparation of Nanoscale Ag Semishell Array with Tunable Interparticle Distance and Its Application in Surface-Enhanced Raman Scattering

Nanoscale Ag semishell arrays with controlled size and tunable interparticle distance were prepared by combining nanosphere lithography with reactive ion etching. First, a large-area ordered monolayer of polystyrene (PS) nanospheres was deposited on glass substrates using the Langmuir−Blodgett (LB) technique. The PS spheres with different diameters were employed in LB procedures. Second, the monolayers of PS spheres were etched to control the diameter and tune the interparticle distance. Finally, a Ag layer was evaporated on the etched PS templates. Ag films with periodical nanostructures were obtained and can be used as surface-enhanced Raman scattering (SERS) substrates. These substrates exhibited homogeneity and good enhancement ability. SERS enhancement factor (EF) was represented on the order of 104−105. The correlation between nanoscale morphology and SERS activity of the substrates was investigated. When the size of Ag-semishell was fixed, the EF value decreased with the increase of interparitcle d...

Monitoring Lipids Uptake in Neurodegenerative Disorders By SECARS Microscopy

In this study, we investigated a novel application of Surface-Enhanced Coherent anti-Stokes Raman Scattering (SECARS) microscopy for imaging intravenously injected ultra small paramagnetic iron oxide nanoparticles (USPION) in Amyotrophic Lateral Sclerosis (ALS) experimental model. Experiments were performed on transgenic rat model, expressing multiple copies of mutant (G93A) human SOD-1 gene (hSOD-1G93A), treated with antibodies against CD4+ T cells magnetically labelled with USPION. Marked intensity enhancements have been observed in specific pathological regions of the ALS brain as compared to the wild-type model. The results obtained correlated SECARS enhancements to selective association of lipids to up-taken USPION which shows high accumulation in the brainstem and midbrain region. The work presented shows the promising potential of SECARS microscopy in investigating neurodegenerative disorders in experimental systems using USPION as molecular nanoprobes. [DOI: 10.1380/ejssnt.2010.362]

Facile Synthesis and One-Dimensional Assembly of Cyclodextrin-Capped Gold Nanoparticles and Their Applications in Catalysis and Surface-Enhanced Raman Scattering

Controlled synthesis of Au nanoparticles with adjustable sizes (10−50 nm) and narrow size distributions (<10% in standard deviation) was realized by reducing hydrochloroauric acid with α-cyclodextrin (α-CD) in an alkaline aqueous solution, which was very simple and “green”. It was revealed that a proper pH was essential to the formation of stable dispersions of nonaggregated Au nanoparticles and a higher pH would lead to the welding of the Au nanoparticles into one-dimensional (1D) wires or three-dimensional (3D) aggregates. Moreover, 1D assembly of α-CD-capped Au nanoparticles into nanochains was readily induced by partial removal of the organic stabilization shell, which resulted from the host−guest interactions between α-CDs capped on Au nanoparticle surfaces and toluene molecules. Finally, the as-prepared Au nanoparticles were found to serve as effective catalyst to activate the reduction of 4-nitrophenol in the presence of NaBH4, and the application of the assembled Au nanoparticle thin film as a substrate for surface-enhanced Raman scattering (SERS) was also demonstrated.

Type I collagen-mediated synthesis of noble metallic nanoparticles networks and the applications in Surface-Enhanced Raman Scattering and electrochemistry

In this paper, we demonstrated an effective enviromentally friendly synthesis route to prepare noble metallic (Au, Ag, Pt and Pd) nanoparticles (NPs) networks mediated by type I collagen in the absence of any seeds or surfactants. In the reactions, type I collagen served as stabilizing agent and assembly template for the synthesized metallic NPs. The hydrophobic interaction between collagen and mica interface as well as the hydrogen bonds between inter- and intra-collagen molecules play important roles in the formation of collagen–metallic NPs networks. The noble metallic NPs networks have many advantages in the applications of Surface-Enhanced Raman Scattering (SERS) and electrochemistry detection. Typically, the as-prepared Ag NPs networks reveal great Raman enhancement activity for 4-ATP, and can even be used to detect low concentration of DNA base, adenine, without any label step. Furthermore, the cyclic voltammograms showed Pt NPs networks have good electrocatalytic ability for the reduction of O2.

Rectangular Silver Nanorods: Controlled Preparation, Liquid−Liquid Interface Assembly, and Application in Surface-Enhanced Raman Scattering

In this paper, we for the first time report a polyol method for large-scale synthesis of rectangular silver nanorods in the presence of directing agent and seeds. This method has some clear advantages including simplicity, high quality, and ease of scaleup. Silver nanowires or silver nanorods with a submicrometer diameter could also be facilely prepared when the reaction parameters are slightly changed. Furthermore, a liquid−liquid assembly strategy has been employed to construct uniform rectangular silver nanorod arrays on a solid substrate which could be used as surface-enhanced Raman scattering (SERS) substrates with high SERS activity, stability, and reproducibility. It is found that the SERS spectra obtained from the probe molecules with the different concentrations show different SERS intensities. As the concentration of 4-aminothiophenol (4-ATP) or rhodamine 6G (R6G) increases, the SERS intensities progressively increase. The enhancement factor for 4-ATP and R6G should be as large as 5.06 × 104 or much larger than the value of 5.06 × 108, respectively. Most importantly, the SERS spectra of R6G on the assembling film are well reproducible at different sites on a substrate, with a standard deviation of <20%. Our results will open new possibilities for applying SERS to detect different analytical species due to the good reproducibility of the present SERS substrate.

Spontaneous Formation of Two-Dimensional Gold Networks at the Air−Water Interface and Their Application in Surface-Enhanced Raman Scattering (SERS)

Two-dimensional (2-D) gold networks were spontaneously formed at the air−water interface after HAuCl4 reacted with fructose at 90 °C in a sealed vessel, in a reaction in which fructose acted as both a reducing and a protecting agent. Through fine-tuning of the molar ratio of HAuCl4 to fructose, the thus-formed 2-D gold networks can be changed from a coalesced pattern to an interconnected pattern. In the coalesced pattern, some well-defined single-crystalline gold plates at the micrometer-scale could be seen, while in the interconnected pattern, many sub-micrometer particles and some irregular gold plates instead of well-defined gold plates appeared. It is also found that the 2-D gold networks in the form of an interconnected pattern can be used as substrates for surface-enhanced Raman scattering (SERS) because of the strong localized electromagnetic field produced by the gaps between the neighboring particles in the 2-D gold networks.

EDTA-controlled One-pot Preparation of Novel Shaped Gold Microcrystals and Their Application in Surface-enhanced Raman Scattering

Abstract We report a one-pot preparation method for a series of novel shaped gold microcrystals by simply mixing HAuCl4 with disodium salt of ethylenediaminetetraacetic acid (Na2EDTA). Under the different reaction temperatures, spinous structures, multipod microspheres, and rough surfaced microspheres were obtained. These microcrystals exhibit high surface-enhanced Raman scattering (SERS) activity.

Type I Collagen-Mediated Synthesis and Assembly of UV-Photoreduced Gold Nanoparticles and Their Application in Surface-Enhanced Raman Scattering

We reported a simple method to synthesize gold nanoparticles (NPs) by photoreducing HAuCl4 in acetic acid solution in the presence of type I collagen. It was found that the collagen takes an important role in the formation of gold NPs. The introduction of collagen made the shape of the synthesized gold nanocrystals change from triangular and hexangular gold nanoplates to size-uniform NPs. On the other hand, thanks to the special characters of collagen molecules, such as its linear nanostructure, are positively charged when the pH < 7, and the excellent self-assembly ability, photoreduced gold NPs were assembled onto the collagen chains and formed gold NPs films and networks. A typical probe molecule, 4-aminothiophenol, was used to test the surface-enhanced Raman scattering activity of these gold NPs films and networks and the results indicated good Raman activity on these substrates.

Combining Micron-Size Glass Spheres with Silver Nanoparticles to Produce Extraordinary Field Enhancements for Surface-Enhanced Raman Scattering Applications

Using Mie theory and a T-matrix method, we have studied the interaction of light with a micron-size glass sphere and a dimer of silver nanoparticles in order to assess the feasibility of surface-enhanced Raman scattering (SERS) that combined dielectric hot spots with plasmon excitation. We show that when light interacts with glass spheres, there is a robust hot spot on the surface in the forward direction with dimensions of a few hundred nanometers both parallel and perpendicular to the surface. For a glass sphere in vacuum with a refractive index of 1.9 and a radius of 4 μm, we find that the electric field enhancement at this hot spot is |E| 2 = 500. If a dimer of silver particles (spheres of radius 30 nm placed 2 nm apart) is placed at this hot spot, the peak near-field between the nanoparticles is found to be |E| 2 = 7x10 6 . This enhancement factor, which is approximately the product of the dimer-only enhancement factor (∼104) and the hot spot enhancement, is comparable to the largest field enhancements that we have obtained with other nanoparticle structures. It is large enough that the observation of single molecule SERS might be possible with this structure.

Templated Assembly of Gold Nanoparticles into Microscale Tubules and Their Application in Surface-Enhanced Raman Scattering

We report a simple procedure to assemble gold nanoparticles into hollow tubular morphology with micrometer scale, wherein the citrate molecule is used not only as a reducing and capping agent, but also as an assembling template. The nanostructure and growth mechanism of microtubes are explored via SEM, TEM, FTIR spectra, and UV-vis spectra studies. The incorporation of larger gold nanoparticles by electroless plating results in an increase in the diameter of microtubes from 900 nm to about 1.2 microm. The application of the microtubes before and after electroless plating in surface-enhanced Raman scattering (SERS) is investigated by using 4-aminothiophenol (4-ATP) as probe molecules. The results indicate that the microtubes both before and after electroless plating can be used as SERS substrates. The microtubes after electroless plating exhibit excellent enhancement ability.