Surface-enhanced Raman Scattering Active Substrate Research Articles

A novel method for SERS active substrates based on Au/PDMS self-assembled nanocracks

A novel method for a novel type of surface enhanced Raman scattering (SERS) active substrate is proposed with high enhancement and strong sensitivity advantages. It is based on nanoscale Au film nanocracks coated on polydimmethyl siloxane (PDMS) substrate which forms gold/ polydimethylsiloxane (Au/PDMS) nanocomposites. The width of the coated nanocracks ranges from 10 nm to 45 nm by self-assembled. It is concluded that the ratio of main agent to firming agent of PDMS at 9:1 is optimum value for SERS due to its complicate texture of cracks. An enhancement factor (EF) as high as 3.14 * 108 is achieved for 4-Mercaptobenzoic acid molecules adsorbed on the Au/PDMS nanocomposite substrates.

Surfactant-assisted preparation of surface-enhanced Raman scattering-active substrates

As shown in the literature, cationic surfactant hexadecyltrimethylammonium bromide (CTAB) has been predominantly employed in the shape-controlled synthesis of Au nanoparticles (NPs) in solution to produce the corresponding shape-dependent Au NP catalysts. Among the different techniques used to obtain rough metal substrates with surface-enhanced Raman scattering (SERS) activities, controllable and reproducible surface roughness can be generated using an electrochemical process. In this work, innovative SERS-active substrates with Au NPs are prepared for the first time using sonoelectrochemical deposition-dissolution cycles (SEDDCs) in CTAB-containing electrolytes. Encouragingly, the SERS intensity for both the model probe molecule Rhodamine 6G (R6G) and the general example molecule 4-mercaptopyridine (4-MPy) adsorbed onto the developed substrates are higher by more than one order of magnitude compared with R6G and 4-MPy adsorbed onto SERS-active substrates prepared in solutions in the absence of CTAB. Moreover, the limits of detection (LOD) recorded for the developed SERS-active substrates are as low as 2 × 10−15 and 1 × 10−10 M for R6G and 4-MPy, respectively.

Comparison of Surface-Enhanced Raman Scattering Spectra of Azo Dye Sudan III on Several Substrates

ABSTRACT On several substrates, including dried silver-coated filter paper, electro-polishing aluminum foils, and anodic aluminum oxide (AAO) nanometer array templates, surface-enhanced Raman scattering (SERS) spectra of Azo Dye Sudan III molecules were studied, and high-quality SERS spectra were obtained, which indicated that electro-polishing aluminum foils and AAO nanometer array templates were also active SERS substrates. A number of additional modes were presented, as well as some split peaks, which were especially obvious on electro-polishing aluminum foil and AAO nanometer array template. The enhancement mechanisms were discussed and the enhancement factors G were calculated as 104, 106, and 105, respectively.

Surface enhanced Raman scattering of molecules related to highly ordered gold cavities

We presented a controlled particles‐in‐cavity (PIC) pattern for surface‐enhanced Raman scattering (SERS) detection. The periodic gold cavity array was fabricated by electrodeposition using highly ordered polystyrene spheres as a template. The as‐prepared gold cavities can be used as a SERS active substrate with significant spectral enhancement and reproducibility, which was evaluated by SERS signals using 4‐mercaptobenzoic acid (4‐MBA) as probe molecules. The surface of these gold cavities was further functionalized with cetyltrimethylammonium bromide molecules, which may immobilize the 4‐MBA‐modified silver nanoparticles in the gold cavity to form a PIC structure via the electrostatic interaction. We have demonstrated that there exists a pH window for the immobilization of the nanoparticles inside cavities. Therefore, the silver nanoparticles can be selectively immobilized into the functionalized gold cavities under the optimized pH value of the media. Further enhancement of the Raman scattering of the labeled molecules can be achieved due to the interconnection between the silver nanoparticles and gold cavity. Copyright © 2013 John Wiley & Sons, Ltd.

Focused-ion-beam-fabricated Au nanorods coupled with Ag nanoparticles used as surface-enhanced Raman scattering-active substrate for analyzing trace melamine constituents in solution

A well-ordered Au-nanorod array with a controlled tip ring diameter (Au_NRsd) was fabricated using the focused ion beam method. Au_NRsd was then coupled with Ag nanoparticles (Ag NPs) to bridge the gaps among Au nanorods. The effect of surface-enhanced Raman scattering (SERS) on Au_NRsd and Ag NPs/Au_NRsd was particularly verified using crystal violet (CV) as the molecular probe. Raman intensity obtained from a characteristic peak of CV on Au_NRsd was estimated by an enhancement factor of ≈107 in magnitude, which increased ≈1012 in magnitude for that on Ag NPs/Au_NRsd. A highly SERS-active Ag NPs/Au_NRsd was furthermore applied for the detection of melamine (MEL) at very low concentrations. Raman-active peaks of MEL (10−3 to 10−12M) in water or milk solution upon Au_NRsd or Ag NPs/Au_NRsd were well distinguished. The peaks at 680 and 702cm−1 for MEL molecules were found suitable to be used as the index for sensing low-concentration MEL in a varied solution, while that at 1051cm−1 was practical to interpret MEL molecules in water or milk solution bonded with Au (i.e., Au_NRsd) or Ag (i.e., Ag NPs/Au_NRsd) surface. At the interface of Ag NPs/Au_NRsd and MEL molecules in milk solution, a laser-induced electromagnetic field or hotspot effect was produced and competent to sense low-concentration MEL molecules interacting with Ag and Au surfaces. Accordingly, Ag NPs/Au_NRsd is very promising to be used as a fast and sensitive tool for screening MEL in complex matrices such as adulteration in e.g., food and pharmaceutical products.

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 3×107 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.

Surface-enhanced Raman scattering (SERS) spectroscopy: a versatile spectroscopic and analytical technique used in nanoscience and nanotechnology

Surface-enhanced Raman scattering (SERS) effect deals with the enhancement of the Raman scattering intensity by molecules in the presence of a nanostructured metallic surface. The first observation of surface-enhanced Raman spectra was in 1974, when Fleischmann and his group at the University of Southampton, reported the first high-quality Raman spectra of monolayer-adsorbed pyridine on an electrochemically roughened Ag electrode surface. Over the last thirty years, it has developed into a versatile spectroscopic and analytical technique due to the rapid and explosive progress of nanoscience and nanotechnology. This review article describes the recent development in field of surface-enhanced Raman scattering research, especially fabrication of various SERS active substrates, mechanism of SERS effect and its various applications in both surface sciences and analytical sciences.

Synthesis of Silver Nanoplates with Fibronectin Nanofibril Template and Their SERS Applications

In this work, a novel strategy is provided to prepare silver nanoplates by a fibronectin (Fn) nanofibril template. First, Fn molecules were controlled to assemble into amyloid-like nanofibrils in highly concentrated ethanol aqueous solution. The resultant nanofibrils could serve as a soft template to direct the formation of silver nanoplates. It is worth noting that the silver nanoplates are excellent surface-enhanced Raman scattering (SERS) substrate with 4-aminothiophenol (4-ATP) molecule as a test probe. This high active SERS substrate can also be used to detect drug molecule, 2-thiouracil with high sensitivity.

Laser-induced jets of nanoparticles: exploiting air drag forces to select the particle size of nanoparticle arrays

In this study, we developed a new method-based on laser-induced jets of nanoparticles (NPs) and air drag forces-to select the particle size of NP arrays. First, the incident wavelength of an excimer laser was varied to ensure good photo-to-thermal energy conversion efficiency. We then exploited air drag forces to select NPs with sizes ranging from 5 to 50 nm at different captured distances. Controlling the jet distances allowed us to finely tune the localized surface plasmon resonance (LSPR) wavelength. The shifting range of the LSPR wavelengths of the corresponding NP arrays prepared using the laser-induced jet was wider than that of a single NP or an NP dimer. We further calculated the relationship between the air drag force and the diameter of the NPs to provide good control over the mean NP size (capture size ≧ 300 μm) by varying the capture distance. Laser-induced jets of NPs could also be used to fabricate NP arrays on a variety of substrates, including Si, glass, plastic, and paper. This method has the attractive features of rapid, large-area preparation in an ambient environment, no need for further thermal annealing treatment, ready control over mean particle size, and high selectivity in the positioning of NP arrays. Finally, we used this method to prepare large NP arrays for acting hot spots on surface-enhanced Raman scattering-active substrates, and 10(-12) M R6G can be detected. Besides, we also prepare small NP arrays to act as metal catalysts for constructing low-reflection, broadband light trapping nanostructures on Si substrates.

SILVER NANOPARTICLES FILMS DEPOSITED ON AAO TEMPLATES BY THERMAL EVAPORATION FOR SURFACE-ENHANCED RAMAN SCATTERING OF R6G

Silver nanoparticles (NPs) films with different nominal thicknesses were deposited on the anodic aluminum oxide (AAO) templates with pore diameter about 200 nm by thermal evaporation. These NPs films were used as the surface enhanced Raman scattering (SERS) active substrates. The microstructure and surface morphology of the films were studied by X-ray diffraction and scanning electron microscopy, respectively. The SERS activity of the films was investigated by Raman scattering of adsorbed rhodamine 6G (R6G) at different concentrations. The results revealed that the average diameter of Ag NPs in different samples is 58 nm, 75 nm, 93 nm and 108 nm, respectively. Ag NPs film on AAO template is very suitable as a SERS active substrate and can detect R6G molecules with a concentration of 10-8 M. The intensity of the SERS spectra is related to both the Ag NPs size and interparticle distance. The sample with an average particle diameter of 93 nm has the highest SERS enhancement factor (1.3 × 106).

Facile synthesis of chitosan-mediated gold nanoflowers as surface-enhanced Raman scattering (SERS) substrates

Metal nanoflowers are the most attractive substrate for surface-enhanced Raman scattering (SERS) due to many hot-spots on their surfaces. This paper worked on the facile fabrication of gold nanoflowers (AuNFs) through the reduction of HAuCl4 with ascorbic acid in the presence of chitosan polymers. The resulting AuNFs exhibited controllable size, morphology, and plasmon-derived absorption by adjusting the chitosan concentration, pH of the solution, and dosage amounts of ascorbic acid. X-ray diffraction (XRD) patterns showed face-centered cubic (fcc) structure for these nanoflowers. As-prepared AuNFs were successfully employed as an active SERS substrate in the sensitive detection of 2-chlorothiophenol (10−4M).

Gold Nanoparticle Aggregates Preparation by (3-aminpopropyl)- Trimethoxysilane for Highly Active SERS Substrates

A simple preparation method of gold nanoparticle aggregates for highly active surface enhanced Raman scattering (SERS) substrates is developed by adding APS to gold sol under vigorous magnetic stirring. The optical and morphological properties of these aggregates are examined by UV-vis spectroscopy and atomic force microscopy. It is found that the SERS activity of the new synthesized gold nanoparticle aggregates is about 200 higher than that of single gold nanoparticles with Rhodamine 6G(R6G) probe.

Surface-enhanced Raman scattering (SERS) spectra of three kinds of azo-dye molecules on silver nanoparticles prepared by electrolysis

Silver nanoparticles were prepared by an electrolysis method. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were employed to detect the morphology of these particles. Based on this high active surface enhanced Raman scattering (SERS) substrate, three kinds of azo-dye molecules (Methyl Yellow, Methyl Red and Sudan Red 1) were carefully studied. Using the Gaussian’98 software, we gained the calculation result of these three kinds of azo-dye molecules, and found that the calculation results had good concordance with the experimental one. The detection limit of azo-dye molecules on the silver nanoparticles can go down to 10−5mol/l, which indicated that these particles were an active SERS substrate.

Functional hybrid nickel nanostructures as recyclable SERS substrates: detection of explosives and biowarfare agents

We present the synthesis of highly anisotropic nickel nanowires (NWs) and large area, free-standing carpets extending over cm(2) area by simple solution phase chemistry. The materials can be post-synthetically manipulated to produce hybrid tubes, wires, and carpets by galvanic exchange reactions with Au(3+), Ag(+), Pt(2+), and Pd(2+). All of these structures, especially the hybrid carpets and tubes, have been prepared in bulk and are surface enhanced Raman scattering (SERS) active substrates. Molecules of relevance such as dipicolinic acid (constituting 5-15% of the dry weight of bacterial spores of Bacillus anthracis), dinitrotoluene, hexahydro-1,3,5-triazine (RDX), and trinitrotoluene at nanomolar concentrations have been detected. An enhancement factor of ∼10(10) was observed for the Ni-Au nanocarpet. The reusability of the Ni-Au nanocarpet for SERS applications was tested 5 times without affecting the sensitivity. The reusability and sensitivity over large area have been demonstrated by Raman microscopy. Our method provides an easy and cost effective way to produce recyclable, large area, SERS active substrates with high sensitivity and reproducibility which can overcome the limitation of one-time use of traditional SERS substrates.

A facile strategy for obtaining fresh Ag as SERS active substrates

A facile strategy has been reported to obtain on-line fresh Ag as surface-enhanced Raman scattering (SERS) active substrates by making AgCl nanoparticles exposed to the laser beam of Raman spectrometer. The composition and morphology of AgCl nanoparticles were characterized by X-ray diffraction (XRD), UV–visible (UV–vis) spectroscopy and scanning electron microscopy (SEM). The laser-driven evolvement and possible formation mechanism of cubic AgCl nanoparticles to Ag/AgCl composites were also investigated by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and high-resolution transmission electron microscopy (HRTEM). Raman measurements demonstrate that the fresh Ag nanoparticles with a few defects have a prominent SERS sensitivity to probe molecules, such as the 4-mercaptopyridine (4-Mpy) and 4-aminothiophenol (PATP) molecules. The SERS intensity of 4-Mpy and PATP increases up to the maximum when the laser irradiation time is prolonged to 50s, which corresponds to the defect extent and the proportion of fresh Ag in the Ag/AgCl composites. This work provides a simple, efficient and feasible approach for obtaining on-line fresh Ag as SERS substrates.

Hydrothermally Roughened Surface-Enhanced Raman Scattering-Active Substrates with Low Background Signals for Chemical Sensing Application

A low-cost, environment friendly and easily fabricated SERS-active substrate with low background signals has been developed by hydrothermal treatment of titanium thin films deposited on silicon substrate. Results from the experimental study revealed that Rhodamine 6G can be well resolved using gold-coated hydrothermally roughened TiO2 substrates. The effect of surface enhancement by the hydrothermally roughened substrates enables rapid identification of Rhodamine 6G, and the enhancement capability is controllable by tuning the surface roughness of the substrates through varying treatment duration. The hydrothermally treated TiO2 substrates also exhibit tunable wettability like that of the untreated ones.

A new strategy to prepare surface-enhanced Raman scattering-active substrates by electrochemical pulse deposition of gold nanoparticles

In this communication, we develop a simple pathway to prepare SERS-active substrates with Au nanoparticles (NPs) by an electrochemical strategy of deposition-dissolution cycles (DDCs). The prepared SERS-active substrates demonstrate large Raman scattering enhancement for Rhodamine 6G (R6G) with a detection limit of 2 × 10(-12) M and an enhancement factor of 5.8 × 10(7).

Comparative study of surface-enhanced Raman scattering activities of three kinds of silver colloids when adding anions as aggregating agents

The surface enhanced Raman scattering (SERS) spectrum of methylene blue (MB) varies observably when using different kinds of silver colloids as SERS active substrates. The colloids were synthesized by three different methods. Sodium chloride, sodium sulfate, sodium nitrate were chosen as aggregating agents in this study. Three kinds of anions were performed on hydroxylamine-reduced silver colloid and the effect of the chloride anion was investigated in the three SERS-active colloids. From the results it can be concluded that the interaction between analyte and silver nanoparticles is different in different kinds of colloidal environments and the addition of anions also has a great influence on SERS spectrum. The effects on the SERS spectra were qualitatively explained through the study of SERS spectra for various silver colloids and aggregating agents in this paper.

New Surface-Enhanced Raman Scattering Active Substrate Fabricated by Use of the Langmuir−Blodgett Technique

A new method of fabrication of a substrate for surface-enhanced Raman scattering (SERS) is proposed. The substrate is a layer of Ag nanoparticles on a solid surface, where the nanoparticles are syn...

Guiding Molecules with Electrostatic Forces in Surface Enhanced Raman Spectroscopy

In surface enhanced raman scattering (SERS) the problem of drawing molecules to the places where surface plasmon resonance enhancements will produce signals is one of the most basic ones, and the initial obstacle to every application of the effect. We explore the possibility of using electrostatic forces as a means to "guide" charged molecules in solution toward SERS active substrates. We also show explicitly the possibility of selectively enhancing different types of dyes according to their charge, and we discuss briefly possible extensions for other applications where "electrostatic guiding" could be an option.