Two-step femtosecond laser pulse train fabrication of nanostructured substrates for highly surface-enhanced Raman scattering

A simple and repeatable method using femtosecond laser pulse train to fabricate nanostructured substrates with silver nanoparticles over a large area for surface-enhanced Raman scattering is reported. The method involves two steps: (1)?femtosecond laser pulse train micromachining and roughening and (2)?femtosecond laser processing of the substrates in a silver nitrate solution. Surface modification is investigated experimentally by varying the time delay of the double femtosecond laser pulse train. With time delay ranging from 200 to 600?fs, the different enhancement factors were observed. This study demonstrates that a maximum enhancement factor of 6.8×10⁶, measured by 10^-6 M Rhodamine 6G solution, can be achieved at the time delay of 400?fs.     

Silver-coated Si nanograss as highly sensitive surface-enhanced Raman spectroscopy substrates

We created novel surface-enhanced Raman spectroscopy (SERS) substrates by metalization (Ag) of Si nanograss prepared by a Bosch process which involves deep reactive ion etching of single crystalline silicon. No template or lithography was needed for making the Si nanograss, thus providing a simple and inexpensive method to achieve highly sensitive large-area SERS substrates. The dependence of the SERS effect on the thickness of the metal deposition and on the surface morphology and topology of the substrate prior to metal deposition was studied in order to optimize the SERS signals. We observed that the Ag-coated Si nanograss can achieve uniform SERS enhancement over large area (∼1 cm ×1 cm) with an average EF (enhancement factor) of 4.2×10⁸ for 4-mercaptophenol probe molecules. Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorized users.     

Nanoscale metal pillar arrays on elastomeric substrates for surface-enhanced Raman spectroscopy platform

The nanostructures found in nature sometimes have elaborate, three-dimensional structures that consist of soft and flexible constituents, and which exhibit diverse mechanical and optical functions. Here, we introduce a facile, low-cost and scalable nanofabrication approach based on a hot embossing process that can replicate sub-micron to nanoscale features on elastomeric substrates. We have further developed this technique to achieve polymer/metal heterostructure nanopillar arrays via conformal coating of Au films on polymeric templates. Each nanopillar displays a smooth surface and a constant diameter along the vertical direction. Raman spectroscopy studies revealed that the metallic nanostructures decorated with methylene blue exhibited a dominant Raman peak at 1624 cm⁻¹ that was enhanced more than 3000 times and seven times relative to bare planar Si and Au-coated planar polystyrene substrates, respectively. These results indicate that our nanopillar array can be exploited as a flexible, large area platform for surface-enhanced Raman spectroscopy.     

Silver fractal networks for surface-enhanced Raman scattering substrates

Based on diffusion-limited aggregation process, a convenient nanotechnique is demonstrated to obtain large silver fractal networks for a surface-enhanced Raman scattering (SERS)-active substrate. The silver fractal networks are of high SERS enhancement factor, large dynamical range. The observed SERS efficiency can be explained in terms of strongly localized plasmon modes relative to the single particle plasmon resonance.     

Ion beam engineered nano silver silicon substrates for surface enhanced Raman spectroscopy

We demonstrate a method for engineering substrates for surface enhanced Raman spectroscopy (SERS) by Ag⁻ ion implantation in Si. The implantation dose and beam current density are chosen such that the Ag concentration in Si exceeds the solid solubility limit, causes aggregation of Ag and nucleates Ag nano particles. The embedded nano particles are then partially exposed by a wet etch process. Our measurements show that the so fabricated nano‐composite substrates are very effective as stable and reproducible SERS substrates. Copyright © 2013 John Wiley & Sons, Ltd.     

Sensitive surface-enhanced Raman scattering substrates based on anti-pyramidal gold architectures decorated with silver nanoparticles

Abstract

A micro-structured gold surface, consisting of a periodic square–based anti–pyramidal array (Klarite) with a smooth boundary surface on which silver nanoparticles (diameter: 60?nm) were deposited, produced an active surface enhanced Raman scattering substrate. With p-aminothiophenol as a probe molecule, the Raman activity of the micro–structured surface was compared before and after deposition of the silver nanoparticles. Experimental results show that the Raman spectra on the silver/p-aminothiophenol/Klarite structure is stronger than that on the silver/p-aminothiophenol/gold film and the Raman spectra on the silver/p-aminothiophenol/gold film is stronger than that on silver/p-aminothiophenol, p-aminothiophenol/Klarite structure, p-aminothiophenol/gold film, which is confirmed by numerical simulations. A similar result is obtained with crystal violet as test molecule.     

Raman and surface-enhanced Raman spectroscopy evidence for oxidation-induced decomposition of graphite

It has been proposed that reduction of exfoliated graphite oxide could be a potential method for producing large quantities of graphene. Raman and surface-enhanced Raman spectroscopy are used to show that oxidation of graphite and exfoliated graphite significantly increases the defect structure of both materials. This would likely lead to a heavily defected graphene structure when oxygen is removed. To insure the observed decomposition is not due to the laser light, the effect of laser intensity on the materials was investigated. It was found that at the highest laser intensity (1.4 × 10⁸ W/M²) there was a significant increase in defects. However, lower laser intensity was found which did not produce defects and was used in the studies of the effect of oxidation on the spectra.     

A durable plastic substrate for surface-enhanced Raman spectroscopy

A novel durable substrate has been prepared for surface-enhanced Raman spectroscopy (SERS). The substrate is fabricated by reduction of silver nitrate using poly(vinyl pyrrolidone) (PVP) polymer as stabilizers. The SERS-active particles are based on poly(methylmethacrylate) (PMMA) materials, producing stable and optically translucent substrates. The stability of silver particles on the substrate was demonstrated by characterizing the localized surface plasmon resonance (LSPR) band of the elemental silver particles. The SERS activity was evaluated by detecting the signal from Raman probe molecules, Rhodamine 6G (R6G). This plastic substrate material is easy to prepare, inexpensive, and sturdy for SERS applications.     

Microbiological identification by surface-enhanced Raman spectroscopy

New methods for pathogens identification are of growing interest in clinical and food sectors. The challenge remains to develop rapid methods that are more simple, reliable, and specific. Surface-enhanced Raman spectroscopy (SERS) appears to be a promising tool to compete with current untargeted identification methods. This article presents the intensive research devoted to the use of SERS for bacterial identification, from the first to the very recent published results. Compared to normal Raman spectroscopy, the introduction of nanoparticles for SERS acquisition introduces a new degree of complexity. Bacterial Raman fingerprints, which are already subject to high spectral variability for a given strain, become then very dependent on numerous experimental parameters. To overcome these limitations, several approaches have been proposed to prepare the sample, from the microbiological culture conditions to the analysis of the spectrum including the coupling of nanoparticles on the bacterial membrane. Main strategies proposed over the last 20 years are examined here and discussed in the perspective of a protocol transfer towards industry.     

Single-site surface-enhanced Raman scattering beyond spectroscopy

Recent progress in the observation of surface-enhanced Raman scattering (SERS) is reviewed to examine the possibility of finding a novel route for the effective photoexcitation of materials. The importance of well-controlled SERS experiments on a single molecule at a single site is discussed based on the difference in the information obtained from ensemble SERS measurements using multiple active sites with an uncontrolled number of molecules. A single-molecule SERS observation performed at a mechanically controllable breaking junction with a simultaneous conductivity measurement provides clear evidence of the drastic changes both in the intensity and in the Raman mode selectivity of the electromagnetic field generated by localized surface plasmon resonance. Careful control of the field at a few-nanometer-wide gap of a metal nanodimer results in the modification of the selection rule of electronic excitation of an isolated single-walled carbon nanotube. The examples shown in this review suggest that a single-site SERS observation could be used as a novel tool to find, develop, and implement applications of plasmon-induced photoexcitation of materials.     

Computer simulation of surface-enhanced Raman scattering in nanostructured metamaterials

The simulation of local field fluctuations and surface-enhanced Raman scattering in percolation systems at the percolation threshold is described. An approximate real-space renormalization group method was used in the simulation. It allows one to radically reduce the computation time compared to an exact calculation and to obtain detailed information about the electromagnetic field. The local fields in real macroscopic systems can be calculated by using this approximation. A computer simulation of the local fields in metal island (percolation) films has been performed by the developed method. The calculation has confirmed the existence of giant local field fluctuations. In turn, the local electric field excites Raman scattering. The local fields of surface-enhanced Raman scattering have been calculated for the first time. The dependence of the Raman scattering enhancement factor on the reference frequency and Stokes shift has been derived. An experimental observation of this dependence could be considered as a confirmation of the electromagnetic nature of the enhancement.     

Controlling the properties of silver nanoparticles deposited on surfaces using supercritical carbon dioxide for surface-enhanced Raman spectroscopy

Silver nanoparticles (AgNPs) have been deposited on silicon and glass surfaces via a supercritical carbon dioxide (sc-CO₂) synthesis route for application in surface-enhanced Raman spectroscopy (SERS). Arrhenius plots revealed that nucleation and growth processes in this system depend on both temperature and surface chemistry. Results also demonstrated that temperature and surface chemistry could be varied to control nanoparticle properties, such as the mean nanoparticle size, density, and surface coverage, providing two useful variables for manipulating the properties of AgNPs deposited on surfaces in this system. These data also provide scientific insight into the underlying mechanisms governing heterogeneous AgNP deposition on a substrate in a sc-CO₂ system in addition to engineering insight into the variables that can be used to manipulate AgNP characteristics. The mean particle size could be tuned over the range 20–200 nm, the interparticle distance could be tuned over the range 70 nm–1 μm, and the surface coverage could be tuned over the range 0.035–0.58. Products were analyzed by scanning electron microscopy with image analysis, transmission electron microscopy, X-ray diffraction, and SERS. The silver nanoparticle-coated substrates were successfully applied in SERS, detecting the model analyte Rhodamine 6G at a concentration of 1 μM, a three orders of magnitude improvement over SERS surfaces previously fabricated in sc-CO₂ systems. Such surfaces can find use in trace concentration analyte detection in biomedical, chemical, and environmental applications.     

Gold nanoparticle-coated silicon cone array for surface-enhanced Raman spectroscopy

ABSTRACT

We demonstrate a silicon cone array substrate coated with gold nanoparticles and which was highly sensitive, homogeneous, and provided a large area for surface-enhanced Raman spectroscopy (SERS). A deep reactive ion-etching process was used to fabricate the high-density silicon cone array, and gold nanoparticles were formed on the silicon cone surface by magnetron sputtering. The substrate was tested with 10^?6 M rhodamine 6 G solution. Enhancement of the substrate was about 60-fold greater than that of flat substrate. Moreover, SERS signals obtained from 24 random areas on the substrate showed good homogeneity with an average standard deviation of 3.9%.     

Detection of explosive vapour using surface-enhanced Raman spectroscopy

A commercially available nano-structured gold substrate was used for activating surface-enhanced Raman scattering (SERS). Raman spectra of the vapour of explosive material, triacetonetriperoxide (TATP), at trace concentrations produced from adsorbed molecules on such surfaces have been studied. Prominent Raman lines of the explosive molecular species were recorded at a sample temperature of ∼35°C, which is near to human body temperature. For this study, the concentration of the adsorbed TATP molecules on the nano-structured surface was varied by heating the sample to different temperatures and exposing the substrate to the sample vapour for different lengths of time. The intensities of the Raman lines have been found to increase with the increase in temperature and also with the increase in the duration of exposure for a fixed temperature. However, as expected, the Raman intensities have been found to saturate at higher temperatures and longer exposures. These saturation effects of the strengths of the Raman lines in the SERS of TATP vapour have been investigated in this paper. The results indicate that the optimisation for vapour deposition on the surface could be a crucial factor for any quantitative estimate of the concentration of the molecular species adsorbed on the nano-structured substrates.     

Fabrication and surface-enhanced Raman scattering (SERS) of Ag/Au bimetallic films on Si substrates

Ag films on Si substrates were fabricated by immersion plating and served as sacrificial materials for preparation of Ag/Au bimetallic films by galvanic replacement reaction. The formation procedure of films on the surface of Si was studied by scanning electron microscopy (SEM), which revealed Ag films with island and dendritic morphologies experienced novel structural evolution process during galvanic replacement reaction, and nanostructures with holes were produced within the resultant Ag/Au bimetallic films. SERS activity both of sacrificial Ag films and resultant Ag/Au bimetallic films was investigated by using crystal violet as an analyte. It has been shown that SERS signals increased with the process of galvanic substitution and reached intensity significantly stronger than that obtained from pure Ag films.     

Self-assembly 2D plasmonic nanorice film for surface-enhanced Raman spectroscopy

As an ultrasensitive sensing technology, the application of surface enhanced Raman spectroscopy (SERS) is one interesting topic of nano-optics, which has huge application prospectives in plenty of research fields. In recent years, the bottleneck in SERS application could be the fabrication of SERS substrate with excellent enhancement. In this work, a two-dimensional (2D) Ag nanorice film is fabricated by self-assembly method as a SERS substrate. The collected SERS spectra of various molecules on this 2D plasmonic film demonstrate quantitative detection could be performed on this SERS substrate. The experiment data also demonstrate this 2D plasmonic film consisted of anisotropic nanostructures has no obvious SERS polarization dependence. The simulated electric field distribution points out the SERS enhancement comes from the surface plasmon coupling between nanorices. And the SERS signals is dominated by molecules adsorbed at different regions of nanorice surface at various wavelengths, which could be a good near IR SERS substrate for bioanalysis. Our work not only enlarges the surface plasmon properties of metal nanostructure, but also exhibits the good application prospect in SERS related fields.     

Disease-related proteins determination based on surface-enhanced Raman spectroscopy

Abstract

Surface-enhanced Raman spectroscopy (SERS) is a promising platform for simple, rapid, and economical protein quantitation and analysis and can achieve much lower detection limits for the ultrasensitive detection of proteins and a much wider linear concentration range for quantitative analysis than other methods can. In addition, SERS can provide a large amount of fingerprint information for the individual components of a mixture through SERS effects, which are sensitive and selective for different types of proteins and protein mixtures. In general, the occurrence and development of diseases are accompanied by changes in the content or structure of biomarkers (disease-related proteins). Here, we provide an overview of the SERS technique and its applications to disease-related protein determination. Different diseases, such as Alzheimer’s disease (AD), cardiac muscle tissue injury, and multicancer, are discussed and exhibit potential utility in biomarker detection and diagnosis. SERS opens a new path to the early diagnosis of critical diseases, which will effectively reduce human suffering and mortality.     

银岛膜表面胸腺嘧啶吸附行为的表面增强拉曼光谱和表面增强红外光谱研究

利用激光刻蚀法制备了具有化学纯净表面的银岛膜,该岛膜有很好的表面增强特性。利用表面增强拉曼光谱和表面增强红外光谱对胸腺嘧啶分子在银岛膜表面的吸附状态进行了对比研究。表面增强拉曼光谱中CN和C—O伸缩振动模式的出现表明胸腺嘧啶分子由原来的酮式结构变成了烯醇式结构;C(4)O伸缩振动谱带明显增强和N(3)的去质子化异构体特征峰的存在证明胸腺嘧啶分子是通过O(8)和N(3)的共同作用倾斜地吸附在银岛膜表面。对10-5 mol.L-1胸腺嘧啶在银岛膜表面上的红外光谱利用欧米采样器进行了反射法测量,发现其红外吸收增强了200倍。红外信号分析的结果支持了胸腺嘧啶分子通过O(8)与银表面发生相互作用的论断,同时也可得出胸腺嘧啶倾斜地吸附在银岛膜表面的结论。     

Propagating surface plasmon polaritons for remote excitation surface-enhanced Raman scattering spectroscopy

To illustrate the attractive potentials of remote-excitation surface enhanced Raman scattering (RE-SERS), we review the fundamental concepts and typical applications of propagating surface plasmon polaritons (PSPPs). Based on the RE-SERS technic, the adsorbed molecules are protected from being directly illuminated, while the merits of SERS still remained. However, the critical limitations of applying RE-SERS hinder its rapid development. Hence, drawing an overview about the PSPPs would be beneficial for further promoting the significance of RE-SERS in biological application and investigating the mechanism of surface catalytic reactions.     

Large-area surface-enhanced Raman scattering-active substrates fabricated by femtosecond laser ablation

A rapid and simple approach to fabricate large-area surface-enhanced Raman scattering-active(SERS-active) substrates is reported.The substrates are fabricated by using femtosecond laser(fs-laser) direct writing on Silicon wafers,followed by thin-film coating of metal such as gold.The substrates are demonstrated to exhibit signal homogeneity and good enhancement ability for SERS.The maximum enhancement factor(EF) up to 3×10 7 of such SERS substrates for rhodamine 6G(R6G) at 785 nm excitation wavelength was measured.This technique could demonstrate a functional microchip with SERS capability of signal homogeneity,high sensitivity and chemical stability.