Surface-enhanced Raman scattering spectroscopy monitoring and degradation of organic pollutants using a novel nanowire.

A multifunctional Ag/AlOOH nanowires (ANW) composite substrate was constructed, which not only accomplishes highly sensitive detection of organic dye molecules, but also has excellent performance in the degradation of pollutants. The ANW in the Ag/ANW substrate possesses a high aspect ratio, which extends the distribution area of Ag and enables a large number of hot spots on the active substrate. Additionally, due to the abundant OH groups on the ANW, there is an increased number of anchor sites for adsorbed metal ions in the Ag/ANW compound, thus contributing to the enhancement and degradation of molecules. Moreover, the constructed multifunctional Ag/ANW nanocomplexes also show great promise for practical applications, providing a reference for the detection and degradation of contaminants.

The novel sandwich composite structure: a new detection strategy for the ultra-sensitive detection of cyclotrimethylenetrinitramine (RDX).

This study presents a novel sandwich composite structure that was designed for the ultra-sensitive detection of cyclotrimethylenetrinitramine (RDX). Au nanorod arrays (Au NRAs) were prepared and bound to 10-7M 6-MNA as adsorption sites for RDX, while Au nanorods (Au NRs) were modified using 10-5M 6-MNA as SERS probes. During detection, RDX molecules connect the SERS probe to the surface of the Au NRAs, forming a novel type of Au NRAs-RDX-Au NRs 'sandwich' composite structure. The electromagnetic coupling effect between Au NRs and Au NRAs is enhanced due to the molecular level of the connection spacing, resulting in new 'hot spots'. Meanwhile, Au NRAs and Au NRs have an auto-enhancement effect on 6-MNA. In addition, the presence of charge transfer in the formed 6-MNA-RDX complex induced chemical enhancement. The limits of detection of RDX evaluated by Raman spectroscopy using 6-MNA were as low as 10-12mg ml-1(4.5 × 10-15M) with good linear correlation between 10-12and 10-8mg ml-1(correlation coefficientR2 = 0.9985). This novel sandwich composite structure accurately detected RDX contamination in drinking water and on plant surfaces in an environment with detection limits as low as 10-12mg ml-1and 10-8mg ml-1.

SERS based monitoring of toluene vapors at ambient and elevated temperatures by using a ruffled silver nanolayer as a substrate.

The authors describe a Surface enhanced Raman spectroscopy (SERS)-based method for the detection of gaseous toluene at different temperature regimes using 3D ruffled silver SERS substrates and a commercially available handheld Raman system equipped with a 785 nm laser. The 3D silver SERS substrates were synthesized via electroless deposition of silver on the ruffled sandpaper and HF-etched silicon wafers. The morphological characterization of the silver SERS substrates was carried out by atomic force microscopy and scanning electron microscopy. UV-Vis spectroscopy absorption spectra of the silver nanostructures showed plasmonic peaks at 522 nm and 731 nm. Toluene vapors were collected with a syringe at ambient temperature and at 100 °C, while SERS detection was always performed at room temperature. Toluene detection was based on the measurement of the Raman bands at 787 cm-1 and 1003 cm-1 (in the fingerprint region). The method allow gaseous toluene to be detected at its vapor concentrations of 522 ppm (mg/L), 261 ppm (mg/L) and 26 ppm (mg/L). Graphical abstract Schematic presentation of an original method for the detection of toluene vapors by SERS technique. The collection of toluene vapors was carried out at room and at high temperatures. The vapors were transferred to methanol by bubbling. The SERS measurements were carried out at room temperature.

High SERS performance of functionalized carbon dots in the detection of dye contaminants.

INTRODUCTION: The long-term overuse of malachite green (MG) has potential carcinogenic, teratogenic, and mutagenic effects. The functional nanocomposite is novel and challenging to construct and implement through surface enhanced Raman scattering (SERS) strategy to reveal the contributions in application. OBJECTIVES: The novel Ag-CDs (carbon dots)-PBA (phenyl boric acid) nanocomposite was constructed by a facile route to detect toxic MG molecule with high SERS sensitivity and good uniformity. METHODS: The enhanced substrate used for the detection of MG has been successfully constructed using PBA modulated Ag-CDs on a structured surface with rich binding sites. RESULTS: The fabricated Ag-CDs-PBA substrate can be used to analyze various probe molecules exhibiting high sensitivity, good signal reproducibility, and excellent stability. The mechanism between components has been proved by calculations originating from the plasmonic Ag and active electronic transmission among the bridging CDs and PBA via the close spatial π-π effect. In addition, the accelerated separation of electron-hole pairs was triggered to further improve the SERS activity of the hybrid via a bidirectional charge transfer (CT) process. Significantly, the Ag-CDs-PBA system shows distinctive selectivity, in which PBA can hinder the interference of other species without specific hydroxyl groups. CONCLUSION: Based on this deeper insight on plasmon-mediated mechanism, the SERS substrate was successfully practiced for quantitative determination in real water and fish samples. The strategy developed promises to be a new sensor technology and has great potential for environmental and food safety applications.

Plasmonic Ag decorated AlOOH for highly sensitive SERS detection of affinity OH groups molecules enriched in hotspots.

Significant breakthroughs have been made in the development of surface-enhanced Raman scattering (SERS) substrates constructed by depositing plasmonic Ag onto nanostructured platforms. AlOOH is widely fabricated using hydrothermal, microwave, and microemulsion methods. Among these, the high catalytic activity of AlOOH prepared by the microemulsion method is derived from its high specific surface area, more active surface OH groups, and multi-active adsorption sites. And nanomaterials with such excellent properties have not yet been fabricated on a SERS-based platform to improve the Raman-enhanced properties of Ag achieving high-sensitivity detection of probe molecules especially with affinity for OH groups. The precious metal Ag has long been known to serve as traps to capture electrons and holes generated by plasmon resonance, reducing electron-hole recombination and exhibiting high activity in photocatalytic processes. In this work, to demonstrate the SERS substrate activity of the AlOOH@Ag complex, it has been successfully applied to identify congo red (CR) molecules with high sensitivity, methyl blue (MB) and methyl orange (MO), enabling trace-level detection with enhanced performance much stronger than Ag substrate.

Synergistic enhancement effect of MoO3@Ag hybrid nanostructures for boosting selective detection sensitivity.

An ex situ method was used to synthesize noble metals and metal oxide composite materials, due to the selective adsorption properties of metal oxides, the adsorption of different probe molecules by this composite structure had been studied. In the ex situ approach, we use (3-aminopropyl) diethoxy methylsilane (ATES) as a coupling agent which is easy for noble metal nanoparticles deposited on metallic oxide nanomaterials. The Raman scattering (SERS) substrate of 1D MoO3 nanowires (MoO3-NWs) @Ag nanoparticles (Ag-NPs) hybrid surface had been fabricated. Several parameters are presented in the following which influences the morphology of self-assembly and SERS activity: (i) coupling agent of ATES, (ii) ATES content (iii) Ag-NPs content. The finite difference time domain (FDTD) method is to explain the enhancement mechanism distribution of the hybrid substrate. Different probe molecules (R6G, Methylene Blue, Crystal Violet, and 4-ATP) have been adsorbed for SERS tests. Improved principle component analysis (PCA) is adopted to obtain the minimum detection limit of probe molecules. Through the DFT calculation, different absorption strengths between the target molecules and the MoO3(010) surface have been illustrated, which is also the main reason for the selective enhancement effect of MoO3@Ag hybrid nanostructures. This paper might propose a method to prepare such enhancement substrate based on the selective absorption properties of oxide semiconductors.

The Effect of Surface Modification of Gold Nanotriangles for Surface-Enhanced Raman Scattering Performance.

A surface modification of ultraflat gold nanotriangles (AuNTs) with different shaped nanoparticles is of special relevance for surface-enhanced Raman scattering (SERS) and the photo-catalytic activity of plasmonic substrates. Therefore, different approaches are used to verify the flat platelet morphology of the AuNTs by oriented overgrowth with metal nanoparticles. The most important part for the morphological transformation of the AuNTs is the coating layer, containing surfactants or polymers. By using well established AuNTs stabilized by a dioctyl sodium sulfosuccinate (AOT) bilayer, different strategies of surface modification with noble metal nanoparticles are possible. On the one hand undulated superstructures were synthesized by in situ growth of hemispherical gold nanoparticles in the polyethyleneimine (PEI)-coated AOT bilayer of the AuNTs. On the other hand spiked AuNTs were obtained by a direct reduction of Au3+ ions in the AOT double layer in presence of silver ions and ascorbic acid as reducing agent. Additionally, crumble topping of the smooth AuNTs can be realized after an exchange of the AOT bilayer by hyaluronic acid, followed by a silver-ion mediated reduction with ascorbic acid. Furthermore, a decoration with silver nanoparticles after coating the AOT bilayer with the cationic surfactant benzylhexadecyldimethylammonium chloride (BDAC) can be realized. In that case the ultraviolet (UV)-absorption of the undulated Au@Ag nanoplatelets can be tuned depending on the degree of decoration with silver nanoparticles. Comparing the Raman scattering data for the plasmon driven dimerization of 4-nitrothiophenol (4-NTP) to 4,4'-dimercaptoazobenzene (DMAB) one can conclude that the most important effect of surface modification with a 75 times higher enhancement factor in SERS experiments becomes available by decoration with gold spikes.

Ionic Liquid-Modulated Synthesis of Porous Worm-Like Gold with Strong SERS Response and Superior Catalytic Activities.

Porous gold with well-defined shape and size have aroused extensive research enthusiasm due to their prominent properties in various applications. However, it is still a great challenge to explore a simple, green, and low-cost route to fabricate porous gold with a "clean" surface. In this work, porous worm-like Au has been easily synthesized in a one-step procedure from aqueous solution at room temperature under the action of ionic liquid tetrapropylammonium glycine ([N3333][Gly]). It is shown that the as-prepared porous worm-like Au has the length from 0.3 to 0.6 µm and the width of approximately 100-150 nm, and it is composed of lots of small nanoparticles about 6-12 nm in diameter. With rhodamine 6G (R6G) as a probe molecule, porous worm-like Au displays remarkable surface enhanced Raman scattering (SERS) sensitivity (detection limit is lower than 10-13 M), and extremely high reproducibility (average relative standard deviations is less than 2%). At the same time, owing to significantly high specific surface area, various pore sizes and plenty of crystal defects, porous worm-like Au also exhibits excellent catalytic performance in the reduction of nitroaromatics, such as p-nitrophenol and p-nitroaniline, which can be completely converted within only 100 s and 150 s, respectively. It is expected that the as-prepared porous worm-like Au with porous and self-supported structures will also present the encouraging advances in electrocatalysis, sensing, and many others.

One-Step Synthesis of Au-Ag Nanowires through Microorganism-Mediated, CTAB-Directed Approach.

Synthesis and applications of one dimensional (1D) metal nanostructures have attracted much attention. However, one-step synthesis of bimetallic nanowires (NWs) has remained challenging. In this work, we developed a microorganism-mediated, hexadecyltrimethylammonium bromide (CTAB)-directed (MCD) approach to synthesize closely packed and long Au-Ag NWs with the assistance of a continuous injection pump. Characterization results confirmed that the branched Au-Ag alloy NWs was polycrystalline. And the Au-Ag NWs exhibited a strong absorbance at around 1950 nm in the near-infrared (NIR) region, which can find potential application in NIR absorption. In addition, the Au-Ag NWs showed excellent surface-enhanced Raman scattering (SERS) enhancement when 4-mercaptobenzoic acid (MBA) and rhodamine 6G (R6G) were used as probe molecules.