Surface-enhanced Raman Scattering Analysis Research Articles

Sensitive and Homogeneous Surface‐Enhanced Raman Scattering Detection Using Heterometallic Interfaces on Metal–Organic Framework‐Derived Structure

AbstractHere the use of heterometallic interfaces on metal–organic framework‐derived structures as surface‐enhanced Raman scattering (SERS)‐active substrates is investigated for sensitive and homogeneous SERS detection. Zeolitic imidazole framework‐67 (ZIF‐67) is grown on a conductive glass substrate via chemical bath deposition, followed by carbonization and oxidation to form ZIF‐67‐derived Co3O4 (ZIF‐67‐CO). For the sensitive and homogeneous SERS analysis, ZIF‐67‐CO is converted to the heterometallic interface Au–Ag@ZIF‐67‐derived Co3O4 (denoted as Au–Ag@ZIF‐67‐CO) via electrodeposition and successive chemical grafting. The optical properties of Au–Ag@ZIF‐67‐CO indicate a uniform and large‐scale distribution of both metals on the surface. Raman signals from the substrate are evenly enhanced based on the Raman intensity and shift mapping over a large area. Due to the multiple absorption bands of the Au–Ag@ZIF‐67‐CO substrate, signal enhancement can also be achieved with two different laser sources (532 and 785 nm) that are frequently used in SERS. As a result, concentration‐dependent and fingerprint SERS signals of small molecules such as 1,2‐bis‐(4‐pyridyl) ethylene, Nile blue A, and 1,1′‐diethyl‐2,2′‐cyanine iodide are obtained, and their signal enhancement factors are 104–105. Collectively, the use of heterometallic‐interfaced ZIF‐67‐CO will be a beneficial approach for collecting reproducible SERS signals of various target analytes.

Silver@mesoporous Anatase TiO2 Core-Shell Nanoparticles and Their Application in Photocatalysis and SERS Sensing

Nanostructured noble metal-semiconductor materials have been attracting increasing attention because of their broad application in the field of environmental remediation, sensing and photocatalysis. In this study, a facile approach for fabricating silver@mesoporousanataseTiO2 (Ag@mTiO2) core-shell nanoparticles employing sol-gel and hydrothermal reaction is demonstrated. The Ag@mTiO2nanoparticles display excellent surface-enhanced Raman scattering (SERS) sensitivity and they can detect the methylene blue (MB) molecules with the concentration of as low as 10−8 M. They also exhibit outstanding photocatalytic activity compared with mTiO2, due to the efficient separation and recombination restrain of electron–hole pairs under ultraviolet light. The Ag@mTiO2nanoparticles also present good stability and they can achieve recyclable photocatalytic degradation experiments for five times without loss of activity. Subsequently, the nanoparticles with dual functions were successfully used to in situ monitor the photodegradation process of MB aqueous solution. These results, demonstrating the multifunctional Ag@mTiO2 nanoparticles, hold promising applications for simultaneous SERS analysis and the removal of dye pollutants in environmental field.

Simulation of Surface Enhanced Raman Scattering From Nanoparticles With Wideband Nested Equivalence Source Approximation

Surface Enhanced Raman Scattering (SERS) has been widely used in the fields of surface science, spectral analysis, biosensors, and biomedical detection. A wideband nested equivalent source approximation (WNESA) accelerated method of moments (MoM) of multiple material regions is proposed, for the analysis of SERS by nanostructure. The SERS affected by the diameter and distance between gold nanospheres for dimer structure is studied through numerical simulations with WNESA. It is found that nanoparticles-based SERS substrates with different dimensions and distances will produce different excitation wavelengths and SERS enhancement factors, by evaluating the variation of hot spot positions with wavelengths. The computational complexity of WNESA for SERS substrate simulation is <i>O</i>(<i>N</i> log <i>N</i>), where <i>N</i> is the number of unknowns. Significant improvement of the design efficiency of nanostructures for increasing the magnitude of SERS can be achieved.

Cicada Wing Inspired Au@Ag Nanodome-Cones Array Chip for Sensitive and Reproductive Surface-Enhanced Raman Scattering Analysis of Sprouts and Beverages

Cicada Wing Inspired Au@Ag Nanodome-Cones Array Chip for Sensitive and Reproductive Surface-Enhanced Raman Scattering Analysis of Sprouts and Beverages

Ag Nanorods for Label-Free Surface-Enhanced Raman Scattering Analysis of Cancer Cells from Cell Lysates

Ag Nanorods for Label-Free Surface-Enhanced Raman Scattering Analysis of Cancer Cells from Cell Lysates

Synthesis of Ag nanoparticles decorated CeO2 nanocomposite material for effective SERS analysis

New efficient surface enhanced raman scattering (SERS) nanocomposite material namely silver nanoparticles (AgNPs) decorated Cerium Oxide (AgNPs@CeO2) was synthesized by adopting simple citrate reduced, precipitation and deposition methods. The synthesized AgNPs@CeO2 material was characterized with UV-DRS, FTIR, Raman, FESEM, EDX and HRTEM analyses. The obtained results reveal the formation of AgNPs@CeO2 nanocomposite material with high purity. The FESEM image result confirms that the Ag NPs are decorated on the surface of CeO2. This AgNPs@CeO2 nanocomposite was used for fabrication of SERS substrate by drop casted on glass slide. Similarly, for comparative purpose, the pure AgNPs and CeO2NPs were also fabricated individually on glass slide. The SERS properties for newly fabricated AgNPS@CeO2, AgNPs and CeO2 NPs substrate were examined by employed in to detection of 4-aminothiophenol (4-ATP) as a model Raman reporter molecule/analyte. The newly designed AgNPs@CeO2 material showed excellent SERS properties and sensitivity than that of AgNPs and CeO2NPs substrates. The enhanced SERS properties noticed in AgNPs@CeO2 are due to the charge transfer, electromagnetic effect and more hot spots present in metal on metal oxide surfaces. Therefore, it is suggested that the AgNPs@CeO2 composite material with excellent SERS properties will have an intensive scope for detection of medically significant single analyte/molecule and hence study in that direction are continuing. Copyright © 2018 VBRI Press.

Instant Preparation of Ultraclean Gold Nanothorns under Ambient Conditions for SERS Kit-Enabled Mobile Diagnosis.

Availability of surface-enhanced Raman scattering (SERS) substrates with good stability, high sensitivity, and a clean surface is crucial for the practical usefulness of the SERS technology in biochemical sensing, especially for point-of-care testing (POCT). Hereby, we develop a "ready-to-use" SERS kit, which requires only 20 s to fabricate ultraclean gold nanothorn (AuNT)-based SERS chips under ambient conditions with simple solution processing steps. By varying the thickness of the pre-coated platinum (Pt) nanolayer, we can control the size and number density of the grown AuNT. Taking advantage of the ultraclean surface of the instantly obtained fresh AuNT, Raman reporter molecules can also be immediately modified, by means of which specific detection of three analytes including H2O2, NO2-, and ClO- is realized. Furthermore, we propose the concept of an SERS kit and apply it to smartphone-based Raman analysis for POCT applications. This on-site preparation method solves the long-standing challenges hindering the practical use of SERS substrates, such as complicated fabrication processes, interference of residual surfactants, poor surface stability, and easy contamination. Besides performing SERS analysis conveniently and quickly, this SERS kit-enabled POCT technology can integrate remote data terminals and medical resources, which shows great potential for environmental protection or online-healthcare systems.

Selective recognition and determination of malachite green in fish muscles via surface-enhanced Raman scattering coupled with molecularly imprinted polymers

Molecularly imprinted polymers (MIPs) were incorporated with surface-enhanced Raman scattering (SERS) for selective recognition and rapid detection of malachite green in fish muscles. Among four functional monomers, methacrylic acid was selected as the suitable one for MIPs synthesis based upon computational simulation. The optimized MIP exhibited a higher adsorption efficiency for malachite green than that of nonimprinted polymers. The 74 nm gold-silver core-shell nanoparticles (Au@Ag NPs) provided stronger SERS signals for malachite green than those of other eleven gold nanoparticles and Au@Ag NPs. The use of selected MIP with Au@Ag NPs enabled to detect as low as 0.5–1 ng/g of malachite green in fish muscles from three different species, which was similar to that of 0.5 μg/L for malachite green standard solutions. The limit of detection was 0.37–0.64 ng/g in different fish muscles. This study provided a rapid, selective, and sensitive approach for SERS analysis of malachite green in aquatic products. • Surface-enhanced Raman scattering (SERS) used for malachite green (MG) detection. • Molecularly imprinted polymers (MIPs) designed to capture MG via computer simulation. • From 12 metallic colloid, Au@Ag (dia. 74 nm, seed 43 nm) chosen as a SERS substrate. • As low as 0.5–1 ppb MG in fish muscles detected with MIP-SERS hybrid method. • Interference of sample matrix effects minimized via MIP for SERS detection of MG.

Label-free Surface Enhanced Raman Scattering (SERS) on Centrifugal Silver Plasmonic Paper (CSPP): A Novel Methodology for Unprocessed Biofluids Sampling and Analysis.

Label-free SERS is a powerful bio-analytical technique in which molecular fingerprinting is combined with localized surface plasmons (LSPs) on metal surfaces to achieve high sensitivity. Silver and gold colloids are among the most common nanostructured substrates used in SERS, but since protein-rich samples such as serum or plasma can hinder the SERS effect due to protein–substrate interactions, they often require a deproteinization step. Moreover, SERS methods based on metal colloids often suffer from a poor reproducibility. Here, we propose a paper-based SERS sampling method in which unprocessed human serum samples are first soaked on paper strips (0.4 × 2 cm2), and then mixed with colloidal silver nanoparticles by centrifugation to obtain a Centrifugal Silver Plasmonic Paper (CSPP). The CSPP methodology has the potential to become a promising tool in bioanalytical SERS applications: it uses common colloidal substrates but without the need for sample deproteinization, while having a good reproducibility both in terms of overall spectral shape (r > 0.96) and absolute intensity (RSD < 10%). Moreover, this methodology allows SERS analysis more than one month after serum collection on the paper strip, facilitating storage and handling of clinical samples (including shipping from clinical sites to labs).

Mesoporous One-Component Gold Microshells as 3D SERS Substrates.

Surface-enhanced Raman scattering (SERS) is a powerful analytical tool for label-free analysis that has found a broad spectrum of applications in material, chemical, and biomedical sciences. In recent years, a great interest has been witnessed in the rational design of SERS substrates to amplify Raman signals and optionally allow for the selective detection of analytes, which is especially essential and challenging for biomedical applications. In this study, hard templating of noble metals is proposed as a novel approach for the design of one-component tailor-made SERS platforms. Porous Au microparticles were fabricated via dual ex situ adsorption of Au nanoparticles and in situ reduction of HAuCl4 on mesoporous sacrificial microcrystals of vaterite CaCO3. Elimination of the microcrystals at mild conditions resulted in the formation of stable mesoporous one-component Au microshells. SERS performance of the microshells at very low 0.4 µW laser power was probed using rhodamine B and bovine serum albumin showing enhancement factors of 2 × 108 and 8 × 108, respectively. The proposed strategy opens broad avenues for the design and scalable fabrication of one-component porous metal particles that can serve as superior SERS platforms possessing both excellent plasmonic properties and the possibility of selective inclusion of analyte molecules and/or SERS nanotags for highly specific SERS analysis.

A highly sensitive SERS platform based on small-sized Ag/GQDs nanozyme for intracellular analysis

The small-sized plasmonic nanoparticles are easily internalized by cells and organelles, but usually possess poor surface-enhanced Raman scattering (SERS) activity, restricting their promising applications for intracellular SERS analysis. To break the current bottleneck of intracellular SERS application, herein, a uniform and small-sized (ca. 10 nm) core–shell Ag/oxidized graphene quantum dots (o-GQDs) nanohybrids have been prepared. The Ag/o-GQDs inherit unique features with parallel-interlaced stacking of o-GQDs as capping agent, possess the increasing and broadening plasmon adsorption and display a unique edge state charge transfer (CT) resonance in the long-wavelength region of visible light, enabling the enhanced electromagnetic (EM) and CT effect for superior SERS sensitivity at lower energy. Further, the Ag/o-GQDs demonstrate excellent biocompatibility and highly efficient nanozymatically catalytic activity, which are first put forward to integrate efficient SERS with Ag/o-GQDs nanozyme to catalyze peroxidase-like reaction for accurate sensing of the intracellular H2O2 at the subcellular level. Moreover, the Ag/o-GQDs nanozyme-catalyzed reactive oxygen species (ROS) generation and the cancer cell multisubcellular-targeting capability provide a promising strategy for the synergistically catalytic therapy specifically toward tumors. This study illustrates a significant route to design an efficient small-sized noble metal/carbon nanozymatic SERS substrate, and demonstrates an exciting potential for ultrasensitive SERS bioanalysis at the subcellular level.

Au Nanoflowers for Catalyzing and In Situ Surface-Enhanced Raman Spectroscopy Monitoring of the Dimerization of p-Aminothiophenol.

In this work, we demonstrated a facile approach for fabrication of Au nanoflowers (Au NFs) using an amino-containing organosilane, 3-aminopropyltriethoxysilane (APTES), as a shape-directing agent. In this approach, the morphology of the Au particles evolved from sphere-like to flower-like with increasing the concentration of APTES, accompanied by a red shift in the localized surface plasmon resonance peak from 520 to 685 nm. It was identified that the addition of APTES is profitable to direct the preferential growth of the (111) plane of face-centered cubic gold and promote the formation of anisotropic Au NFs. The as-prepared Au NFs, with APTES on their surface, presented effective catalytic and surface-enhanced Raman scattering (SERS) performances, as evidenced by their applications in catalyzing the dimerization of p-aminothiophenol and monitoring the reaction process via in situ SERS analysis.

Simultaneous and Accurate Quantification of Multiple Antibiotics in Aquatic Samples by Surface-Enhanced Raman Scattering Using a Ti3C2Tx/DNA/Ag Membrane Substrate.

Rapid and accurate analysis of multiple targets in complex samples is still a big challenge in the fast detection field. Herein, we developed a rapid and accurate strategy for simultaneous quantification of trace multiple antibiotic residues in complex aquatic samples by surface-enhanced Raman scattering (SERS) using a Ti3C2Tx/DNA/Ag membrane substrate. This membrane substrate was proven to have good uniformity, reproducibility, stability, and SERS activity by a series of characterizations. Also, this substrate combined excellent electromagnetic enhancement and chemical enhancement effects, which endowed it with good sensitivity and selectivity during SERS analysis. It achieved the integration of multitarget separation, enrichment, and in situ detection, which significantly improved the selectivity, sensitivity, accuracy, and detection throughput by membrane substrate coupling with SERS for real-sample analysis. Finally, this rapid SERS analysis strategy was successfully applied to the simultaneous quantification of trace nitrofurantoin (NFT) and ofloxacin (OFX) in aquatic samples. It was observed that trace NFT and OFX were actually detected and simultaneously quantified to be 8.0-13.7 and 42.6-49.1 μg/kg in aquatic samples, respectively, with good recoveries of 88.0-107% and relative standard deviations of 0.3-5.5%. The results were verified by a traditional high-performance liquid chromatography method with relative errors of -9.8 to 5.3%. This strategy provided a methodological reference for accurate SERS quantification of multiple targets in complex samples.

An efficient double template strategy to construct large-area and highly ordered silver “urchin-like” arrays for sensitive SERS analysis

Plasmonic metal nanostructures possessing plentiful gaps or tips have attracted great attention in surface enhanced Raman scattering (SERS) due to their superior performance. Herein, we present an efficient fabrication strategy to construct a large-area and highly ordered 3D silver “urchin-like” array (SULA) based on the ultra-thin alumina membrane (UTAM) mask and the self-assembled polystyrene spheres template. Numerical simulations reveal that the proposed SULA possesses enormous hotspots at the tips of Ag nanocones and in the crevice gaps between the adjacent Ag nanocaps responsible for high sensitivity with an enhancement factor of 1.8 × 106 and excellent reproducibility with a relative standard deviation of 8.3% in SERS analysis. Furthermore, the SULA substrate exhibits great SERS performance for detecting the contaminant crystal violet and thiram in real water environments and excellent linear intensity-concentration dependence relationships. The results indicate the proposed SULAs are promising to be developed as high-performance SERS platforms in qualitative and quantitative trace contaminants in complex water environments.

Thermal-fluid coupling green capture device coupling with Surface-Enhanced Raman Scattering for integrated scheme with rapid separation, enrichment and detection of multi-source formaldehyde in milk

In milk and milk products, the matrix is complex and the interfering components are large, so it is difficult to separate and enrich formaldehyde. In this study, combined with Surface-Enhanced Raman Scattering (SERS) technology, the self-developed green capture device was used to realize the integration of separation, enrichment and detection of formaldehyde. Firstly, we use fluid dynamics to simulate the heat-fluid coupling working mechanism of the enrichment chemical mechanical device. By exploring the steady-state and transient changes of separation and enrichment gas flow under different working conditions, we designed a purge and separation device with small dead volume and high separation efficiency. We further optimized the purge air velocity and heating voltage to increase sample recovery and shorten the separation and enrichment time of the target. As a result, we have realized the application of green and efficient pre-treatment, which is rapid and green. Finally, we used derivatization strategy to enhance the Raman scattering and combined with colloidal gold nanoparticles (AuNPs) to realize SERS analysis. According to this method, we detected formaldehyde in boxed milk, milk powder and raw milk. Thus, we realized a rapid detection method of formaldehyde in milk from various sources, including exogenous and endogenous formaldehyde.

Study on degranulation of mast cells under C48/80 treatment by electroporation-assisted and ultrasound-assisted surface-enhanced Raman spectrascopy

Both electroporation-assisted and ultrasound-assisted delivery methods can rapidly deliver nanoparticles into living cells for surface-enhanced Raman scattering (SERS) detection, but these two methods have never been compared. In this study, electroporation-assisted SERS and ultrasound-assisted SERS were employed to detect the biochemical changes of degranulated mast cells induced by mast cell stimulator (C48/80). The results showed that the cell damage of electroporation based on controllable electric pulse was smaller than that of ultrasound based on cavitation. Transmission electron microscope images of cells indicated that the nanoparticles delivered by electroporation were mainly distributed in the cytoplasm, while ultrasound could transport nanoparticles to the cytoplasm and nucleus. Therefore, electroporation-assisted SERS mainly detects the biochemical information of cytoplasm, while ultrasound-assisted SERS gets more spectral signals of nucleic acid. Both methods can obtain high quality SERS signal of cells. With drug treatment, the SERS peak intensity of 733 cm−1 attributed to phosphatidylserine decreased significantly, which may be due to the activation of mast cell degranulation pathway stimulated by C48/80 agonist, resulting in a large amount of intracellular serine being used to synthesize tryptase, while the production of phosphatidylserine decreased. Further, based on principal component analysis and linear discriminant analysis (PCA-LDA approach), ultrasound-assisted SERS could achieve better sensitivity, specificity and accuracy in the discrimination and identification of drug-treated degranulated mast cells than electroporation assisted SERS. This exploratory work is helpful to realize the real-time dynamic SERS detection of intracellular biochemical components, and it also has great potential in intracellular SERS analysis, such as the cytotoxicity assay of anti-tumor drugs or cancer cell screening.

“Coffee Ring” Effect of Ag Colloidal Nanoparticles Dried on Glass: Impact to Surface-Enhanced Raman Scattering (SERS)

It is well known that spontaneous drying of some fluid droplets on certain solid surfaces forms a “coffee ring” pattern. In this paper, we studied “coffee ring” formation for two kinds of Ag colloidal nanoparticles (borohydride-reduced (b.-r.) and hydroxylamine-reduced (h.-r.)) and its impact on surface-enhanced Raman scattering (SERS). Optical and scanning electron microscopies were used to observe the morphology of the dried rings as well. We used 5,10,15,20-tetrakis(1-methyl-4-pyridyl)porphyrin (TMPyP) as a testing SERS molecular probe. The results showed that the structure of the edge rings of dried drops of Ag colloid/TMPyP systems was different for b.-r. and h.-r. nanoparticles. The inherent limitation of our approach is inhomogeneity in particle and “hot spots” distribution, SERS signal fluctuation, and consequently low spectral reproducibility. However, in the case of h.-r. nanoparticles, it formed a structure with highly enhancing sites (“hot spots”) providing enormous SERS signal of TMPyP. Higher sensitivity and the possibility of spectral mapping over the dried pattern are advantages in comparison with the measurements from colloidal suspension. Although our approach is not reliable for quantitative analytical SERS applications, it can serve as a simple, cheap, and fast prescan method, which can be easily implemented for preliminary SERS analysis.

Qualitative and quantitative detection of corrosion inhibitors using surface-enhanced Raman scattering coupled with multivariate analysis

In this study, a novel strategy was proposed for the on-site detection and quantitation of corrosion inhibitors by means of surface-enhanced Raman scattering (SERS) detection and partial least squares regression (PLSR) algorithm. Using a SERS tape as the signal amplifier, the Raman signals of 2-mercaptobenzothiazole (MBT) inhibitors adsorbed on aluminium alloy were intensively magnified. The SERS intensities grew monotonously with the increase of inhibitor concentration and immersion time, indicating the continuous accumulation of MBT molecules that facilitated the effective corrosion inhibition performance. Furthermore, PLSR method was adopted to achieve the quantitative analysis of inhibitors on metal surface based on the SERS spectra variations. The regression relationship between the SERS spectra of MBT molecules on the alloy surface and their concentrations showed good predictive ability. Based on the established PLSR model, it has been employed for the quantification of remaining MBT inhibitors during reversible desorption process. SERS analysis combined with PLSR algorithm can be used to sensitively detect, quantify and predict corrosion inhibitors, which is helpful for the in-depth understanding of corrosion inhibition mechanism and will promote the exploitation of new corrosion inhibitors.

Ti3C2Tx-AgNPs@beta-cyclodextrin SERS substrate for rapid and selective determination of erythrosin B in dyed food

In this work, a native beta-cyclodextrin capped silver nanoparticles decorated Ti3C2Tx nanosheets (Ti3C2Tx-AgNPs@β-CD) surface-enhanced Raman scattering (SERS) substrate was developed by a facile one-pot method. The two-dimensional Ti3C2Tx nanosheets not only acted as the supporter to load AgNPs, but also served as chemical enhancement material. Meanwhile, β-CD played a critical role in the control of morphology and size of AgNPs, and its supramolecular structure also endowed the Ti3C2Tx-AgNPs@β-CD substrate with selectivity. The Ti3C2Tx-AgNPs@β-CD substrate exhibited excellent sensitivity, good intra-batch and inter-batch reproducibility, and long-term stability by detecting methylene blue model molecule. Then, the substrate was applied for selective determination of erythrosin B among pigment additives via the host-guest size-matching effect. The proposed SERS method with linear range of 1−100 mg/L and detection limit of 30 μg/L could realize rapid SERS analysis of erythrosin B in dyed food samples within 15 min with recoveries of 78.1 %–113.2 %. Erythrosin B was actually found in dyed cherry with 49 mg/kg and marshmallow with 16 mg/kg, and the result matched well with that of UV–vis method. Such a robust substrate possessed great values for efficient and rapid on-site SERS analysis in food safety issues.

Colloidal dendritic nanostructures of gold and silver for SERS analysis of water pollutants

Surface-Enhanced Raman Scattering (SERS) using colloidal metal (Ag, Au) nanoparticles has been regarded as a powerful method for detecting organic pollutants at vestigial levels. Although less investigated, the controlled synthesis of binary nanostructures comprising two metals provides an alternative route to SERS platforms with tuned surface plasmon resonances. Here, we demonstrate that the use of dendrimers allows the formation of distinct combinations of Ag:Au nanostructures that are composed of smaller metal nanocrystals. Our research highlights the role of the dendrimer macromolecules as a multipurpose ligand in the generation of such hybrid nanostructure, including as a reducing agent, an effective long-term colloidal stabilizer and as a molecular glue for interconnecting the primary metal nanocrystals. Noteworthy, the dendrimer-based Ag:Au hybrid nanostructures are more SERS sensitive as compared to the corresponding colloidal blends or to the single-phase metals, as revealed by using molecular pesticides as analytes in spiked water samples. We suggest that the high SERS sensitivity of the hybrid nanostructures is due to interparticle plasmonic coupling occurring between the primary metal nanoparticle aggregates, whose arrangement is templated by the presence of the dendrimer macromolecules.