Highly uniform and optical visualization of SERS substrate for pesticide analysis based on Au nanoparticles grafted on dendritic α-Fe2O3

Plasma-based post-processing of colloidal nanocrystals for applications in heterogeneous catalysis

This review summarizes the work on the use of plasmas to post-process nanostructures, in particular colloidal nanocrystals, as promising candidates for applications of heterogeneous catalysis. Using plasma to clean or modify the surface of nanostructures is a more precisely controlled method compared to other conventional methods, which is preferable when strict requirements for nanostructure morphology or chemical composition are necessary. The ability of plasma post-processing to create mesoporous materials with high surface areas and controlled microstructure, surfaces, and interfaces has transformational potential in catalysis and other applications that leverage surface/interface processes.

The volatile release evaluation of nicotine from snus products under different storage conditions based on surface-enhanced Raman spectroscopy technology

Surface enhanced Raman spectroscopy (SERS) is a highly sensitive analytical detection technique that provides unique chemical and structural information on target molecules. Snus is a type of tobacco product that can release nicotine and other components under certain humidity and temperature without burning, and the evaluation of its nicotine release under different storage conditions is very important for understanding its characteristics, regulating its components, and setting reasonable storage conditions. Herein, by means of an artificial climate box and suction extraction device, the volatile release evaluations of nicotine from snus products under different storage conditions were performed based on Fe3O4 microparticles coated with Au nanorods and Au nanoparticles (Fe3O4@AuNRsNPs) as SERS substrates combined with a capillary. The Fe3O4@AuNRsNPs assemblies can be fixed in the inner wall of the capillary with the aid of an external magnetic field, which improved the maneuverability of the SERS substrates. By comparing the intensities of the spectral peaks of the symmetrical breathing of the pyridine moiety of nicotine molecules with increasing temperature and humidity, which could significantly accelerate the volatile release of a small amount of nicotine, the nicotine release under different conditions could be evaluated. Based on this strategy, it was possible to obtain the storage or placement conditions of the product. The results of this study provide a reference to clarify the volatile release of nicotine under various storage conditions, which is helpful for better regulation of the levels of nicotine in snus. Moreover, such destruction-free evaluation of the volatile release of nicotine from snus products under different storage conditions opens up new perspectives for further research about the impact of nicotinoids on smokers' health and cessation programs.

Detection methods, migration patterns, and health effects of pesticide residues in tea

Due to its rich health benefits and unique cultural charm, tea drinking is increasingly popular with the public in modern society. The safety of tea is the top priority that affects the development of tea industry and the health of consumers. During the process of tea growth, pesticides are used to prevent the invasion of pests and diseases with maintaining high quality and stable yield. Because hot water brewing is the traditional way of tea consumption, water is the main carrier for pesticide residues in tea into human body accompanied by potential risks. In this review, pesticides used in tea gardens are divided into two categories according to their solubility, among which water-soluble pesticides pose a greater risk. We summarized the methods of the sample pretreatment and detection of pesticide residues and expounded the migration patterns and influencing factors of tea throughout the process of growth, processing, storage, and consumption. Moreover, the toxicity and safety of pesticide residues and diseases caused by human intake were analyzed. The risk assessment and traceability of pesticide residues in tea were carried out, and potential eco-friendly improvement strategies were proposed. The review is expected to provide a valuable reference for reducing risks of pesticide residues in tea and ensuring the safety of tea consumption.

Highly sensitive and reproducible CNTs@Ag modified Flower-Like silver nanoparticles for SERS situ detection of transformer Oil-dissolved furfural

Accurately evaluating the aging state of oil paper insulation in electrical equipment is a key to ensure the safe operation of the power transformer. For achieving highly sensitive in-situ detection of dissolved furfural in transformer oil with good reproducibility, flower-like silver nanoparticles modified with carbon nanotubes (CNTs@Ag-F-AgNPs) was synthesized by a combination of electroless silver plating and redox method. The large specific surface area and strong adsorption capacity of CNTs@Ag promoted the formation of more "hot spots". CNTs@Ag-F-AgNPs were adsorbed on Si-Au substrate via mercapto groups on the coupling agent 1'4 phenyldimercaptan molecule (BDT). Using rhodamine 6G (R6G) as probe molecule, the enhanced factor reached 6.96 × 10⁹. Then, the substrate was used for in-situ SERS detection of transformer oil-dissolved furfural at different concentrations and the detection limit was 2.25 mg/L at 1703 cm^-1 (Stretching vibration of C = O in furfural molecule), fulfilling requirements of furfural content detection after severe aging of transformer (4 mg/L). Besides, the relative standard deviation (RSD) of characteristic peak intensity at ten different positions was only 1.74%. These results exhibite that three-dimensional nanostructure with high sensitivity and good reproducibility exhibited a wide application range for in situ detection of dissolved trace furfural in transformer oil.

Simultaneous extraction and surface enhanced Raman spectroscopy detection for the rapid and reliable identification of nicotine released from snus products

Surface enhanced Raman spectroscopy (SERS) is a highly sensitive analytical detection technique that provides unique chemical and structural information on target molecules. Here, simultaneous extraction and SERS detection of nicotine for the rapid and reliable identification of nicotine released from snus products were performed based on a nano-Au assembly hierarchy structure in the capillary. Based on this strategy, the time evolution of the concentrations of nicotine released from the snus products was measured. Through comparison of the intensities of the spectral peaks of the symmetrical breathing of the pyridine moiety of nicotine molecules, with the prolongation of time, the concentration of nicotine released decreased significantly, which is helpful for establishing a method for the rapid evaluation of the processing and selection of excipients of snus products, and provides a new idea for further study of the production of snus pouches and related tobacco products. Moreover, based on data fitting, it can be calculated that the concentration of nicotine in the extraction presented an obvious quadratic relationship with time, and the release of most of the nicotine in the snus pouch, which is held through the gums and palate, was basically completed after ∼15 min. Such destruction-free simultaneous measurements of snus products are opening up new perspectives for further research about the impact of nicotinoids on smokers' health and cessation programs.

The rationality of using coreshell nanoparticles with embedded internal standards for SERS quantitative analysis based glycerol-assisted 3D hotspots platform

Surface enhanced Raman spectroscopy (SERS) is a promising sensing technique that can provide unique chemical and structural fingerprint information, but gaining reliable SERS quantitative data with high sensitivity and stability still remains a challenge. Although using a molecule as an internal standard (IS) can improve the SERS quantitative capability, the reliability and SERS measuring conditions for signal fluctuations during calibration based on IS are yet to be explored when the embedded IS molecules and target objects are located in different environments. Herein, a 3D hotspot matrix SERS platform based on Au@4-MPy@AgNPs was constructed in water with the assistance of glycerol and the dynamic signal changes from the IS, i.e. 4-Mpy, and target molecules were monitored during the process of evaporation with high sensitivity and stability. In contrast to the traditional water-dispersed drying film system, the variation trends of IS and target molecules were consistent in the glycerol-assisted liquid film protection system. Therefore, it is reasonable to calibrate the signal fluctuation by utilizing the embedded IS based on the construction strategy of a glycerol-assisted 3D hotspot platform. This work demonstrates a rational, reliable and precise SERS quantitative technique for testing analyte concentrations in practical systems and has great application prospects in the field of analytical chemistry.

Remarkable SERS Detection by Hybrid Cu2O/Ag Nanospheres

Cu₂O nanospheres (NSs) were synthesized by modifying the glucose reduction method. Based on this method, Cu₂O/Au (Ag) NSs were further prepared by in situ reduction of HAuCl₄ (via electron beam evaporation of Ag). With Rhodamine 6G (R6G) as probe, the surface-enhanced Raman scattering (SERS) characteristics of the three samples were systematically studied. The experiment results showed that the enhancement factor (EF) of Cu₂O/Au (Ag) NSs as 1.25 × 10⁸ (2.74 × 10⁹) and the ultralow detection limit (LOD) as 8.07 × 10^-12 (1.13 × 10^-13) M for R6G. The excellent performance of SERS may be due to the charge transfer (CT) between metal-semiconductor (MS) molecules and the strong electromagnetic field (E-field) of each hot spot. In addition, discrete dipole approximation (DDA) simulations were performed to simulate the E-field enhancement of the Cu₂O and Cu₂O/Au (Ag) NSs in a three-dimensional (3D) configuration. These further supported that the high SERS performance for R6G is because of the powerful E-field coupling between neighboring Au (Ag) NPs and the surface plasmon resonance (SPR) effect. The Cu₂O/Ag NSs have potential in applications such as biomedicine, food safety, and environmental monitoring because of their high sensitivity and good reproducibility.

Synthesis, structure, magnetism and photocatalysis of α-Fe2O3 nanosnowflakes

In this work, a simple one-step hydrothermal method was developed to synthesize high-quality α-Fe2O3 nanoparticles with a snowflake-like microstructure. First, a series of binary supramolecular aggregates were prepared by a non-covalent combination between a polymer such as polyvinylpyrrolidone (PVP) and a complex such as potassium ferrocyanide (PF). Then, the aggregates were used as the precursors of the one-step hydrothermal reactions. The snowflake-like nanostructure has six-fold symmetry as a whole, and each petal is symmetric. This synthesis method has the characteristics of simplicity, rapidity, reliance, and high yield, and can be used for creating high-quality α-Fe2O3 nanoparticles. Moreover, our results show that the molar ratio of PVP to PF, reaction time and temperature play important roles in the generation of a complete snowflake structure from different angles. Also, the snowflake-like α-Fe2O3 nanostructure exhibits a much higher coercivity (2997 Oe) compared to those reported by others, suggesting a strong hysteresis behaviour, which promises potential applications in memory devices, and other fields. Further, the α-Fe2O3 nanosnowflakes show a much higher photocatalytic degradation activity for cationic organic dyes such as crystal violet, rhodamine 6G than for anionic dyes such as methyl orange. A possible photocatalytic mechanism was proposed for explaining the selectivity of the photocatalytic oxidation reaction of organic dyes. We believe that this study provides a direct link among coordination compounds of transition metals, their supramolecular aggregates with polymers, and controlled hydrothermal synthesis of high-quality inorganic metal oxide nanomaterials.

Construction of pure worm-like AuAg nanochains for ultrasensitive SERS detection of pesticide residues on apple surfaces

Ultrasensitive detection of pesticide residues on agricultural products using surface-enhanced Raman spectroscopy (SERS) is of significant interest in food security. Herein, worm-like AuAg nanochains with highly interconnected ultrafine (~6.2 nm) bimetallic particles were developed as an excellent SERS nanosensor via laser-assisted strategy. The SERS detection limit of thiram molecules on apple surfaces is about 10^-7 M (0.03 ppm), which is about 200 times lower than the maximal residue limit (MRL, 7 ppm) in fruit prescribed by the U.S. Environmental Protection Agency (EPA). Importantly, the established excellent linear relationships between the SERS intensities and thiram concentrations can sensitively monitor the slight variation of pesticide residues in agriculture.

The end user sensor tree: An end-user friendly sensor database

Detailed knowledge regarding sensor based technologies for the detection of food contamination often remains concealed within scientific journals or divided between numerous commercial kits which prevents optimal connectivity between companies and end-users. To overcome this barrier The End user Sensor Tree (TEST) has been developed. TEST is a comprehensive, interactive platform including over 900 sensor based methods, retrieved from the scientific literature and commercial market, for aquatic-toxins, mycotoxins, pesticides and microorganism detection. Key analytical parameters are recorded in excel files while a novel classification system is used which provides, tailor-made, experts' feedback using an online decision tree and database introduced here. Additionally, a critical comparison of reviewed sensors is presented alongside a global perspective on research pioneers and commercially available products. The lack of commercial uptake of the academically popular electrochemical and nanomaterial based sensors, as well as multiplexing platforms became very apparent and reasons for this anomaly are discussed.

Functional paper-based SERS substrate for rapid and sensitive detection of Sudan dyes in herbal medicine

There has been an increasing demand for rapid and sensitive techniques for the identification of Sudan compounds that emerged as the most often illegally added fat-soluble dyes in herbal medicine. In this report, we have designed and fabricated a functionalized filter paper consisting of gold nanorods (GNRs) and mono-6-thio-cyclodextrin (HS-β-CD) as a surface-enhanced Raman spectroscopy (SERS) substrate, in which the GNR provides sufficient SERS enhancement, and the HS-β-CD with strong chemical affinity toward GNR provides the inclusion compound to capture hydrophobic molecules. Moreover, the CD-GNR were uniformly assembled on filter paper cellulose through the electrostatic adsorption and hydrogen bond, so that the CD-GNR paper-based SERS substrate (CD-GNR-paper) demonstrated higher sensitivity for the determination of Sudan III (0.1μM) and Sudan IV (0.5μM) than GNRs paper-based SERS substrate (GNR-paper), with high stability after the storage in the open air for 90days. Importantly, CD-GNR-paper can effectively collect the Sudan dyes from illegally adulterated onto samples of Resina Draconis with a simple operation, further open up new exciting opportunity for SERS detection of more compounds illegally added with high sensitivity and fast signal responses.

Multi-branched gold nanostars with fractal structure for SERS detection of the pesticide thiram

The surface-enhanced Raman scattering (SERS) activity of multi-branched gold nanostars with fractal structure has been investigated for trace detection of pesticide thiram. Raman spectrum results show that the gold nanostars substrate can produce about 10² fold stronger signal than the thiram alone with the thiram concentration increase of 10³ times and 1.4 fold stronger signal than the gold nanostars without fractal feature. In the detection procedure, the most prominent SERS peak at 1376cm^-1 has been chosen to characterize and quantify the concentration of thiram. Experimental results indicate this Raman substrate based on fractal gold nanostars exhibits excellent selective probing performance for thiram with a detection limit as low as 10^-10M in solution and 0.24ng/cm² in apple peels. Interference experiment results show that the effects from the interfering pesticides could be neglected in the detection procedure. Therefore, the gold nanostars as a SERS substrate have excellent sensitivity and selectivity.

Controlled synthesis of Cu nanoparticle arrays with surface enhanced Raman scattering effect performance

Herein, we report the synthesis of a 350 nm Cu nanoparticle array with different period combinations by a method based on a monolayer and have further investigated its surface-enhanced Raman scattering (SERS) properties experimentally.

Detection of Pesticide Residues in Food Using Surface-Enhanced Raman Spectroscopy: A Review

Pesticides directly pollute the environment and contaminate foods ultimately being absorbed by the human body. Their residues contain highly toxic substances that have been found to cause serious problems to human health even at very low concentrations. The gold standard method, gas/liquid chromatography combined with mass spectroscopy, has been widely used for the detection of pesticide residues. However, these methods have some drawbacks such as complicated pretreatment and cleanup steps. Recent technological advancements of surface-enhanced Raman spectroscopy (SERS) have promoted the creation of alternative detection techniques. SERS is a useful detection tool with ultrasensitivity and simpler protocols. Present SERS-based pesticide residue detection often uses standard solutions of target analytes in conjunction with theoretical Raman spectra calculated by density functional theory (DFT) and actual Raman spectra detected by SERS. SERS is quite a promising technique for the direct detection of pesticides at trace levels in liquid samples or on the surface of solid samples following simple extraction to increase the concentration of analytes. In this review, we highlight recent studies on SERS-based pesticide detection, including SERS for pesticide standard solution detection and for pesticides in/on food samples. Moreover, in-depth analysis of pesticide chemical structures, structural alteration during food processing, interaction with SERS substrates, and selection of SERS-active substrates is involved.

Simple, Large-Scale Fabrication of Uniform Raman-Enhancing Substrate with Enhancement Saturation

It is well-known that gold nanoparticle (AuNP) clusters generate strong surface-enhanced Raman scattering (SERS). In order to produce spatially uniform Raman-enhancing substrates at a large scale, we synthesized vertically perforated three-dimensional (3D) AuNP stacks. The 3D stacks were fabricated by first hydrothermally synthesizing ZnO nanowires perpendicular to silicon wafers followed by repetitively performing liquid-phase deposition of AuNPs on the tops and side surfaces of the nanowires. During the deposition process, the nanowires were shown to gradually dissolve away, leaving hollow vestiges or perforations surrounded by stacks of AuNPs. Simulation studies and experimental measurements reveal these nanoscale perforations serve as light paths that allow the excitation light to excite deeper regions of the 3D stacks for stronger overall Raman emission. Combined with properly sized nanoparticles, this feature maximizes and saturates the Raman enhancement at 1-pM sensitivity across the entire wafer-scale substrate, and the saturation improves the wafer-scale uniformity by a factor of 6 when compared to nanoparticle layers deposited directly on a silicon wafer substrate. Using the 3D-stacked substrates, quantitative sensing of adenine molecules yielded concentrations measurements within 10% of the known value. Understanding the enhancing mechanisms and engineering the 3D stacks have opened a new method of harnessing the intense SERS observed in nanoparticle clusters and realize practical SERS substrates with significantly improved uniformity suitable for quantitative chemical sensing.

Highly Selective and Repeatable Surface-Enhanced Resonance Raman Scattering Detection for Epinephrine in Serum Based on Interface Self-Assembled 2D Nanoparticles Arrays

Target analyte detection in complex systems with high selectivity and repeatability is crucial to analytical technology and science. Here we present a two-dimensional (2D) surface-enhanced resonance Raman scattering (SERRS) platform, which takes advantages of the high selectivity of the SERRS sensor as well as the sensitivity and reproducibility of the interfacial SERS platform, for detecting trace epinephrine (EP) in the serum. To realize sensitive and selective detection of EP in a complex system, Au NPs are modified with α,β-nitriloacetic acid and Fe(NO₃)₃ to form the Au NP-(Fe-NTA) sensor, and as a consequence, EP can be rapidly captured by the sensor on the surface of Au NPs and then delivered at the cyclohexane/water interface. More importantly, we synthesized the extremely stable Au NPs (PVP-stabilized Au NPs), where the presence of PVP prevents aggregation of Au NPs during the self-assembly process and then makes a more uniform distribution of Au NPs with analytes at the cyclohexane/water interface, approximately 2 nm interparticle distance between the Au NPs, which has been proved by synchrotron radiation grazing incidence small-angle X-ray scattering (SR-GISAXS) experiments. The self-assembly method not only effectively avoids the aggregation of Au NPs and decreases the influence of the background signal but also can capture and enrich EP molecules in the cyclohexane/water interface, realizing the sensitive and selective detection of EP in complex serum sample. This strategy overcomes the difficulty of bringing nanostructures together to form efficient interparticle distance with simple fabrication and maximum uniformity and also provides a powerful nanosensor for tracing amounts of analyte molecules in a complex system with the advantages of capturing and enriching of target molecules in the liquid/liquid interface during the self-assembly process. Our SERRS platform opens vast possibilities for repeatability, sensitivity, and selectivity detection of targets in various complex fields.

Surface-plasmon-induced azo coupling reaction between nitro compounds on dendritic silver monitored by surface-enhanced Raman spectroscopy

Azo coupling reactions with a 4-NTP-functionalized Ag-Ds/GCE composites.

Alteration of the Nonsystemic Behavior of the Pesticide Ferbam on Tea Leaves by Engineered Gold Nanoparticles

A model system consisting of a nonsystemic pesticide (ferbam), engineered gold nanoparticles (AuNPs) and a plant tissue (tea leaves) was investigated using surface enhanced Raman spectroscopy (SERS). Ferbam has no ability by itself to penetrate into tea leaves. When AuNPs were placed with ferbam onto the surface of tea leaves, however, the SERS signal of the ferbam-AuNPs complex was observed inside of the tea leaves. Within 1 h, the ferbam-AuNPs complex rapidly penetrated into the leaf to a depth of approximately 190 μm, about (1)/3 to (1)/2 of the leaf's thickness. The rate of penetration was dependent on the size of AuNPs, with 30 nm AuNPs-ferbam penetrating more rapidly when compared with complexes made with the 50 and 69 nm AuNPs. These results clearly demonstrated an alteration of the nonsystemic behavior of ferbam in the combined presence with AuNPs. This finding might lead to the development of some new pesticide formulations. Conversely, new toxicity issues may arise as the behaviors and fate of pesticides are altered significantly upon interaction with engineered NPs in the pesticide formulation or environment.

Electrochemically fabricated gold dendrites with underpotential deposited silver monolayers for a bimetallic SERS-active substrate

SERS of Ag-covered Au-dendrites (Ag–Au-Ds) outperforms that of Au-Ds at a specific 633 nm laser excitation, and is attributed to improved chemical mechanism (CM) SERS with the Ag–p-NTP bonding and the p-NTP molecular architecture.

A general and rapid approach to hybrid metal nanoparticle–ZnO nanowire arrays and their use as active substrates for surface-enhanced Raman scattering detection

Rapid SERS substrate preparation: an aqueous phase reaction of metal precursors with ZnO@Zn has been exploited for synthesizing SERS-active metal–ZnO nanowire arrays.

Highly Sensitive, Uniform, and Reusable Surface-Enhanced Raman Scattering Substrate with TiO₂ Interlayer between Ag Nanoparticles and Reduced Graphene Oxide

TiO2 nanoparticles and Ag nanoparticles were successively deposited on reduced graphene oxide (rGO) by a two-step solvothermal process to develop a reusable surface-enhanced Raman scattering (SERS) substrate with high sensitivity and uniformity owing to the 2-dimensional planar structure of rGO, the photocatalytic activity of TiO2, and the SERS function of Ag nanoparticles. The presence of TiO2 interlayer efficiently diminished the interference from the Raman intensities of D-band and G-band of rGO and hence enhanced the sensitivity significantly. As compared to Ag/rGO nanocomposite, the detection limit of 4-aminothiophenol (4-ATP) for Ag/TiO2/rGO nanocomposite could be lowered from 10(-10) to 10(-14) M, and its enhancement factor could be raised from 1.27 × 10(10) to 3.46 × 10(12). Meanwhile, good uniformity remained, the relative standard deviation (RSD) value was about 10%. Furthermore, by UV irradiation in water, the photocatalytic property of TiO2 could eliminate the Raman signal of 4-ATP efficiently and made this substrate reusable. After being reused five times, its excellent SERS performance was still retained. Thus, the Ag/TiO2/rGO nanocomposite developed in this work was a promising SERS substrate with good reusability and high sensitivity and uniformity.

Gold nanoisland films as reproducible SERS substrates for highly sensitive detection of fungicides

A wet-chemical approach is used to fabricate centimeter-scale gold nanoisland films (NIFs) with tunable morphology of islands and with strong electromagnetic coupling between them. The approach consists in a uniform seeding of small gold nanoparticles on a glass or silicon substrate, followed by controllable growth of the seeds into small nanoislands. A special technique for TEM sampling was developed to follow the gradual formation of larger-sized isolated nanoparticles, nanoislands of sintered overgrown seeds, and a complete gold layer with nanoscale cracks. The electromagnetic field distribution inside the fabricated NIFs was calculated by FDTD simulations applied to actual TEM images of the fabricated samples rather than to artificial models commonly used. SERS measurements with 1,4-aminothiophenol (ATP) molecules demonstrated the analytical enhancement factor about of 10(7) and the fundamental enhancement factor about of 10(8) for optimized substrates. These values were at least 1 order of magnitude higher than that for self-assembled arrays of gold nanostars and silver nanocubes. SERS spectra of independent samples demonstrated good sample-to-sample reproducibility in terms of the relative standard deviation (RSD) of the main peaks less than 20%. Additionally, Raman maps with 1 μm increment in X-Y directions of NIFs (800 spectral spots) demonstrated good point-to-point repeatability in the intensity of the main Raman vibration modes (RSD varied from 5% to 15% for 50 randomly selected points). A real-life application of the fabricated SERS substrates is exemplified by the detection of the thiram fungicide in apple peels within the 5-250 ppb linear detection range. Specifically, the NIF-based SERS technology detected thiram on apple peel down to level of 5 ng/cm(2).

3D silver nanoparticles decorated zinc oxide/silicon heterostructured nanomace arrays as high-performance surface-enhanced Raman scattering substrates

Three-dimensional (3D) hierarchical nanostructures have been considered as one of the most promising surface-enhanced Raman spectroscopy (SERS) substrates because of the ordered arrangement of high-density hotspots along the third dimension direction. Herein, we reported a unique 3D nanostructure for SERS detection based on silver nanoparticles (AgNPs) decorated zinc oxide/silicon (ZnO/Si) heterostructured nanomace arrays. They were prepared by two steps: (1) Si nanoneedles were grafted onto ZnO nanorod arrays via a catalyst-assisted vapor-liquid-solid (VLS) growth mechanism. (2) AgNPs were rapidly immobilized on the surface of nanomaces by a facile galvanic displacement reaction. The fabricated substrates were employed to detect rhodamine 6G (R6G) with a detection limit down to 10(-16) M, and exhibited a high-enhanced performance (enhancement factor (EF) as high as 8.7 × 10(7)). To illustrate the potential value of the prepared substrates, the different concentrations of melamine aqueous solution (from 10(-4) to 10(-10) M) were detected, and a quantitative relationship between the SERS spectrum intensity and the melamine concentration had been established. In addition, the measure of melamine residual in pure milk was carried out successfully, and the results indicated that the prepared 3D nanomace substrates had great potential in food inspection, environment protection, and a few other technologically important fields.

Hotspot-engineered 3D multipetal flower assemblies for surface-enhanced Raman spectroscopy

Novel 3D metallic structures composed of multipetal flowers consisting of nanoparticles are presented. The control of surface plasmon hotspots is demonstrated in terms of location and intensity as a function of petal number for uniform and reproducible surfaceenhanced Raman spectroscopy (SERS) with high field enhancement.

Nanocrystalline Ag microflowers as a versatile SERS platform

In this paper, the synthesis of Ag microflowers for use as manipulable and reusable substrates in surface enhanced Raman spectroscopy (SERS) is demonstrated, working with ultra-low volumes of the analyte. Flower-like AgBr crystallites with a growth direction of 〈110〉 were first obtained by thermolysing a complex obtained by the stabilization of (AgCl2)(-) anions with tetraoctylammonium bromide. NaBH4 reduction leads to the formation of porous Ag microflowers (50-100 μm) with interconnected nanoparticles. The coupling of the nanoparticles in the microflower results in broadband extinction from visible to IR wavelengths, facilitating SERS using both red and green wavelengths. Using thiophenol as test analyte, uniform SERS enhancement factors in the range of 10(6)-10(8) have been achieved from different parts of the microflower. The microflowers have been used for labeled and non-labeled detection of both single- and double-stranded DNA and using simple manipulation techniques, SERS data have been collected from ultra-low volumes of the analyte solution (∼0.34 nL). The reusability of the substrate for SERS over multiple cycles involving a rapid and efficient wet chemical cleaning procedure is also demonstrated. Finally, by placing the microflower in a microfluidic device, chemical reactions have been examined in situ.

Large-area fabrication of highly reproducible surface enhanced Raman substrate via a facile double sided tape-assisted transfer approach using hollow Au-Ag alloy nanourchins

Ideally, a SERS substrate should possess super signal amplification, high uniformity and reproducibility. Up to now, an emphasis on reproducibility and uniformity has been crucial to ensure consistent chemical detection sensitivity across the surface of a SERS substrate. Here we demonstrate a simple and facile double sided tape-assisted transfer method to fabricate surface enhanced Raman scattering (SERS) substrates with prominent performance using hollow Au-Ag alloy nanourchins (HAAA-NUs). Such a large area, closely-packed flat film of the HAAA-NUs with a high density of "hot spots" exhibits a high SERS activity and reproducibility, simultaneously. The AFM-correlated nano-Raman and the point by point scanning of SERS signals verify the excellent spatial uniformity and reproducibility with a low relative standard deviation (RSD) less than 15% using crystal violet as probe molecule at the concentrations of 1 × 10(-8) M and 1 × 10(-10) M. The SERS signals of Sudan dye at a 1 × 10(-8) M concentration also show high reproducibility with a low RSD of 13.8%. This facile protocol presented here could lead to a high quality SERS substrate and open tremendous potential for various applications.