Surface-enhanced Raman Scattering Properties Research Articles

Controllable Preparation and Size-Dependent SERS Performance of 35–410 nm Quasi-spherical Au NPs

Uniform Au NPs with definite but different sizes will serve as a perfect model for studying the influence of NP size on surface-enhanced Raman scattering (SERS) performance. In this study, using tri-hydroxymethyl aminomethane (Tris-base) as a stabilizer and FeCl2 as a reducing agent, Au NPs with the size of 110–410 nm were prepared by a one-step method by simply changing the amount of FeCl2. In the preparation of small particle size Au NPs, sodium citrate was introduced as an auxiliary stabilizer, and 35–85 nm Au NPs were prepared in one step. In addition, the synthetic Au NPs of different sizes were loaded onto the glass substrate and 4-MOTP was used as the probe molecule to monitor their SERS properties. The results showed that the SERS activity results showed a “volcanic shape” with the change of nanoparticle size at a fixed excitation wavelength. The 160 nm Au NPs have the best SERS performance when the excitation wavelength is 633 nm.

Sensitive detection of malachite green in aquaculture water by surface enhanced Raman scattering using silver coated urchin-like gold nanoparticles

Urchin-like gold nanoparticles (ULGNs) exhibit rich surface plasmon optical properties especially in Surface-enhanced Raman Scattering (SERS) due to their tunable branch number and length. In this work, ULGNs with hollow structure and tunable branches were successfully prepared by the one-pot method. By controlling its morphology, we found the number and length of branches increased with the increase of ascorbic acid. The size of nanoparticles and number of branches decreased with the increase of silver nitrate. To get better SERS activity, we prepared silver coated ULGNs (ULGNs@Ag). When the ULGNs@Ag branches were partially exposed beyond the silver layer, it shows the best SERS properties and we used it as a SERS substrate to complete the detection of malachite green. The linear detection range is from 10−8-10−3 mol·L−1, and the detection limit is 2.5 nmol·L−1, suggesting this research developed a new approach to food safety testing.

MAX phase-derived woolen ball-like K2Ti8O17 with excellent surface-enhanced Raman scattering property

In surface-enhanced Raman scattering (SERS) applications, the MAX phase is typically acid etched to address deficiencies, while the more accessible alkali corrosion products are neglected. The woolen ball-like K2Ti8O17 (KTO) nanomaterial is synthesized via an efficient hydrothermal surface corrosion reaction between KOH solution and MAX phase Ti2AlN, which exhibits excellent SERS capabilities to the contaminating dyes. The enhancement factors are 2.33 × 105, 1.04 × 105 and 2.22 × 105 with lowest limits of detection of 10−7 M, 10−6 M and 10−7 M for crystal violet, rhodamine 6G and methylene blue, respectively, indicating that KTO is a highly desired candidate of SERS substrate material. Meanwhile, KTO shows excellent SERS performance for chrysoidine in simulated seawater, which proves its practical application value. The excellent SERS performance of KTO is attributed to the charge transfer mechanism, which is made possible by the appropriate energy band structure and the robust adsorption capacity. In conclusion, a novel method for the synthesis of KTO is investigated and its reaction process and enhancement mechanism are exhaustively characterized and described. The woolen ball-like KTO exhibits remarkable SERS properties and potential applications.

Combining physical vapor deposition structuration with dealloying for the creation of a highly efficient SERS platform.

Nanostructured noble metal thin films are highly studied for their interesting plasmonic properties. The latter can be effectively used for the detection of small and highly diluted molecules by the surface-enhanced Raman scattering (SERS) effect. Regardless of impressive detection limits achieved, synthesis complexity and the high cost of gold restrict its use in devices. Here, we report on a novel two-step approach that combines the deposition of a silver-aluminum thin film with dealloying to design and fabricate efficient SERS platforms. The magnetron sputtering technique was used for the deposition of the alloy thin film to be dealloyed. After dealloying, the resulting silver nanoporous structures revealed two degrees of porosity: macroporosity, associated to the initial alloy morphology, and nanoporosity, related to the dealloying step. The resulting nanoporous columnar structure was finely optimized by tuning deposition (i.e., the alloy chemical composition) and dealloying (i.e., dealloying media) parameters to reach the best SERS properties. These are reported for samples dealloyed in HCl and with 30 atom % of silver at the initial state with a detection limit down to 10-10 mol·L-1 for a solution of rhodamine B.

“Coffee Ring” Fabrication and Its Application in Aflatoxin Detection Based on SERS

The fabrication of a coffee ring was studied in this work to improve its sensitivity in detecting trace analytes based on surface-enhanced Raman scattering (SERS). Gold nanoparticles were synthesized with diameters of ~40 nm through the sodium citrate reduction method, and rhodamine 6G (R6G) was employed as a probe to evaluate the performance of the fabricated coffee rings. The results showed that the coffee ring formed from the water-washed gold nanoparticles presented more orderly and regular morphology as well as better SERS properties than the unwashed ones. Furthermore, both the concentration and the amount of gold nanoparticles were found to affect its SERS performance. Using the optimized coffee ring as a SERS substrate, trace R6G with a concentration of 5 × 10−8 M was detected. This sensing platform could realize aflatoxin B1 (AFB1) detection down to 5 × 10−7 M and was demonstrated to function well in real-sample testing.

Organic-Inorganic Semiconductor Heterojunction P3HT@Ag2NCN Composite Film as a Recyclable SERS Substrate for Molecule Detection Application

Semiconductor composite materials have attracted interest from surface-enhanced Raman scattering (SERS) substrate research. Here, we investigate an organic-inorganic semiconductor heterojunction P3HT@Ag2NCN composite film as a recyclable SERS substrate for molecule detection application. Our study shows that the SERS substrate of the composite P3HT@Ag2NCN composite film has high sensitivity, excellent signal reproducibility, and is reusable. Significant π-stacking of the probe molecules with the thiophene π-cores molecules from P3HT plays an important role in the large SERS enhancement by the charge transfer mechanism. Due to physical interaction between P3HT and Ag2NCN, the organic-inorganic semiconductor heterojunction structure further improves charge transfer efficiency and the SERS property. Our results show that the enhancement factor (EF) of P3HT@Ag2NCN composite films (EF = 6147 ± 300) for the probe molecule methylene blue is more than 7 times that of P3HT substrate (EF = 848 ± 85) and is about 75 times that of Ag2NCN nanorods (EF = 82 ± 8). In addition, the SERS substrates of the P3HT@Ag2NCN composite film also display excellent reusability and signal reproducibility (RSD < 4.8%). Our study opens up a new opportunity for designing an ideal SERS substrate with high sensitivity, selectivity, long-term stability, low cost, and reusability.

Theoretical Analysis of Hybrid Metal–Dielectric Nanoantennas with Plasmonic Fano Resonance for Optical Sensing

A nanoantenna with Fano response is designed with plasmonic oligomers as a refractive index sensor to enhance surface-enhanced Raman scattering (SERS) in the visible light spectrum. The scattered radiation and field-enhanced interactions of the outer gallium phosphide (GaP) nanoring assembled with an inner heptamer of silver with Fano response are investigated systematically using the finite element method. The characteristics of Fano resonance are found to depend on the size, shape and nature of the materials in the hybrid nanoantenna. The confined electromagnetic field produces a single-point electromagnetic hotspot with up to 159.59 V/m. The sensitivity obtained from the wavelength shift and variation in the scattering cross-section (SCS) shows a maximum value of 550 nm/RIU. The results validate the design concept and demonstrate near-field enhancement, enabling the design of high-performance nanoantennas with enhanced optical sensing and SERS properties.

In-situ reduction of silver nanoparticles on molybdenum disulfide for an ultrasensitive recyclable SERS detection based on electromagnetic and chemical effects

With the aim to realize the extensive implementation of surface enhanced Raman scattering (SERS) technology on practical chemical and biological detection, it is of extreme importance to establish a reliable SERS substrate with promising sensitivity and reusability. In this study, a facile in-situ reduction strategy induced by ultraviolet (UV) irradiation was utilized to modify silver (Ag) nanoparticles onto molybdenum disulfide (MoS2) nanoflowers, facilitating a hybrid substrate with both photocatalytic and SERS properties. An enhancement factor of 5.3 × 106 was achieved in the proposed hybrid substrate, which could realize the photocatalytic diminishing of molecules within 170 min. Particularly, a calibration curve with a limit of detection down to 4.5 × 10−4 mg/mL was demonstrated in the practical recyclable monitoring of carbaryl, which indicates the great potential of the developed MoS2 @Ag composite sample in the monitoring and photo-degradation of trace analytes.

Investigation of Sulfur Doping in Mn-Co Oxide Nanotubes on Surface-Enhanced Raman Scattering Properties.

Doping engineering is an efficient strategy to manipulate the optoelectronic properties of metal oxides for sensing, catalysis, and energy applications. Herein, we have demonstrated the fabrication of sulfur (S)-doped Mn-Co oxides to regulate their band and surface electronic structures, which is beneficial to enhancing the charge transfer (CT) between the metal oxides and their adsorbed molecules. As expected, significantly enhanced SERS signals are achieved on S-doped Mn-Co oxide nanotubes, and the minimum detection concentration can reach as low as 10-8 M. Furthermore, the change in the electronic structure caused by S-doping provides different microelectric fields to influence the orientation of the interaction between the probe molecules and the substrate. Additionally, the evaluation of the oxidase-like catalytic activity of the substrate proved that, with an increase in the ratio of Co2+/Co3+ content, the number of electrons on the substrate increases, which promotes the CT process and further increases the degree of CT. The nonmetallic doping route in semiconducting metal oxides can provide effective and stable SERS activity; moreover, it provides a new strategy for exploring the relationship between CT in catalysis and SERS performance of semiconductors.

Cellular Detection of Glutathione Using Synthesized Stable Sea Urchin-Like Gold Nanoparticles

Gold nanoparticles (AuNPs) have been widely studied in a great mass of cellular biomarkers detection and diagnostics due to their unique combination of physical and optical properties. Sea urchin-like gold nanoparticles (SUL-AuNPs) are well characterized multi-thorn gold nanostructures which possess at least four gold nanothorns on spherical gold surface, mimicking the morphology of sea urchin. Compared to spherical AuNPs, SUL-AuNPs showed a wide variety of light absorption and scattering properties, and the Surface-enhanced Raman Scattering (SERS) properties of SUL-AuNPs were also widely studied dependent on their surface morphology. Herein, three different diameters of SUL-AuNPs based on spherical AuNPs seed-mediated growth method by altering the amount of AuNPs in reaction system had been synthesized. The UV-vis spectrum of synthesized SUL-AuNPs displayed a shift from 550 nm to 650 nm compared to spherical AuNPs. FRET method was applied for the detection of GSH in hepatocytes and cell extracts using rhodamine B (RB) functionalized SUL-AuNPs, among the synthesized three different diameters SUL-AuNPs, 100nm RB-SUL-AuNPs displayed highest sensitivity for GSH detection. What's more, all synthesized SUL-AuNPs turned out to be membrane-permeable, and displayed ignorable cytotoxicity, which make SUL-AuNPs promising cellular thiols detection probes. In particular, it should be noted that the application of RB functionalized SUL-AuNPs exemplify ongoing efforts in design and utility of multifunctional nanoplatforms of SUL-AuNPs.

Lateral Size Effect of Graphene Oxide on Its Surface-Enhanced Raman Scattering Property.

The lateral size effect of graphene oxide (GO) on surfaced-enhanced Raman scattering (SERS) property is systematically investigated by using size-fractionalized GO. For the size fractionalization without changes of chemical structure, large-sized GO (LGO) and small-sized GO (SGO) are separated from the as-synthesized GO (AGO) by centrifugation and membrane filtration, respectively. The size-fractionalized GO sheets are immobilized on a solid substrate for the parallel comparison of their SERS property. As a result, we find that LGO shows considerably higher SERS property than SGO for typical Raman probes such as rhodamine 6G and crystal violet. Furthermore, the lateral size effect of GO derivatives is consistently observed when they are hybridized with plasmonic silver nanoparticles. These results indicate that LGO is superior to AGO and SGO as a SERS platform, and it is also quantitatively confirmed by calculating their enhancement factor.

Constructing Er-Doped ZnO/CuS/Au Core-Shell Nanowires with Enhanced Photocatalytic and SERS Properties

In this study, we fabricated Er-doped ZnO/CuS/Au core-shell nanowires using two-step wet chemical methods and an ion-sputtering method on a glass substrate as a bifunctional photocatalytic and surface-enhanced Raman scattering (SERS) substrate. The characteristic properties of as-prepared photocatalysts were confirmed by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, DR/UV-Vis spectroscopy, and photoluminescence spectroscopy. Compared with Er-doped ZnO nanowires and Er-doped ZnO/CuS core-shell nanowires, Er-doped ZnO/CuS/Au core-shell nanowires exhibited remarkably photocatalytic activity to degrade acid orange 7 solutions under blue LED light. These results ascribed to the Er-doped ZnO/CuS/Au core-shell nanowires can enhance the visible-light absorbance and the separation efficiency of photogenerated electron-hole pairs, inducing their higher photocatalytic activity under blue LED light. In addition, Er-doped ZnO/CuS/Au core-shell nanowires exhibit high sensitivity, a low detection limit (10−6 M), uniformity, recyclability, and stability of SERS performance for detected acid orange 7.

Synthesis of Single- and Few-Layer Nitrogen-doped Graphene and Layer-Dependent Surface-Enhanced Raman Scattering Properties

Synthesis of Single- and Few-Layer Nitrogen-doped Graphene and Layer-Dependent Surface-Enhanced Raman Scattering Properties

Electrochemical Surface Oxidation Enhanced Raman Scattering on Cu

One of the main characteristic of Analytical Chemistry is a constant searching for new methodologies to overcome analytical problems. Minimization of analysis time and sample volumes, replacement of extensive extraction protocols and improvement of selectivity are common tasks in analytical research all around the world. Spectroelectrochemistry is an instrumental technique that totally represents this spirit: The combination of electrochemical set-ups with spectroscopy techniques to study the surface processes has shown to be a powerful technique to resolve complex mixtures of molecules, where analytical signals can present severe interferences [1].Spectroelectrochemistry has been demonstrated to be a powerful analytical technique to study adsorption processes and molecular reactivity on electrode surfaces. More specifically, Raman spectroelectrochemistry (Raman-SEC) combined with plasmonic structures has been demonstrated to be an excellent tool to study molecules at low concentration thanks to Surface Enhanced Raman Scattering (SERS) phenomenon. [2].For almost half a century, Raman-SEC has broadly studied the properties of SERS substrates developed with nanoparticles of plasmonic metals, such as silver, gold and copper, focusing its efforts on the characterization of nanostructures morphology.In 2018, our group discovered a novel methodology to enhance the Raman signal during the electrochemical oxidation of silver electrodes in acidic media [3]. We denoted this phenomenon as Electrochemical Surface Oxidation Enhanced Raman Scattering (EC-SOERS), and represents a phenomenon similar to SERS, because of the enhancement of the Raman signal, but contrary to SERS, since it suggests the loss of plasmonic properties (and thus, Raman enhancement) of metallic structures during the electrochemical oxidation of the plasmonic nanostructures.In this communication, we demonstrate, for the first time, that EC-SOERS can be observed on copper electrodes. This metal, known for its SERS properties, can be also used to enhance selectively the Raman signal during its electrochemical oxidation, detecting different organic molecules with a wide variety of functional groups, opening new gates towards the development of new analytical tools based on EC-SOERS.

From Dilute to Multiple Layers: Bottom‐Up Self‐Assembly of Rough Gold Nanorods as SERS Platform for Quantitative Detection of Thiram in Soil

AbstractThe nanoparticle density (PD) of the substrates is crucial for surface‐enhanced Raman scattering (SERS) performance. Here, bottom‐up SERS substrates based on rough gold nanorods (R‐Au NRs) with different PD are fabricated and their SERS property are investigated. In particular, R‐Au NRs are deposited on the Si wafer from sparse to dense through electrostatic interaction and from monolayer to multiple layers by interface self‐assembly technique. It is found that the SERS intensity increases dramatically with increasing PD and remains almost unchanged when the PD increases to 241.22 counts µm−2, and the limited penetration depth of laser is the reason for the intensity saturation. Additionally, similar results are observed in the smooth Au NRs substrates, re‐confirming the PD‐dependent SERS performance. Importantly, the SERS activity of R‐Au NRs substrates is higher than smooth Au NRs substrates in each PD, indicating that R‐Au NRs can produce stronger electromagnetic field enhancement, which is supported by the theoretical simulation results. Finally, it is demonstrated that the optimal SERS substrates can be effectively utilized for the quantitative measurement of thiram in soil. Briefly, the PD of substrates has a great impact on SERS activity, which offers an idea for the design of highly efficient SERS substrates.

Silver nanoparticle aggregates: Wavelength dependence of their SERS properties in the first transparency window of biological tissues

Silver nanoparticle aggregates are very common substrates for surface enhanced Raman scattering (SERS) due to their simplicity of preparation and good optical enhancement. In this paper, their SERS properties are investigated from 680 to 920 nm, region that spans most of the first transparency window of biological tissues.Our experiments show that the SERS enhancement extends as far as 920 nm, without a significant wavelength dependence: the observed very broad optical response has been interpreted with the formation of large sized aggregates, possibly possessing a partial fractal character. On the other hand, the SERS signal, normalized by the laser power and by the integration time, quickly diminishes from 680 to 920 nm. This happens because the SERS signal depends on the enhancement but also on the instrument sensitivity and on the molecular cross section: for dispersive Raman instruments equipped with silicon CCD detectors and for non resonant molecules, these two parameters tend to diminish towards longer excitation wavelengths.The relevance of these results is twofold. a) Simple silver nanoparticle aggregates are good plasmonic substrates in most of the spectral region in which biological tissues present low absorption. b) The enhancement of the substrate and the normalized SERS signal (that is related to the limit of detection) are not necessarily correlated: they carry complementary pieces of information, both needed for properly designing a SERS experiment.

Self-Assembled Black Phosphorus-Based Composite Langmuir-Blodgett Films with an Enhanced Photocurrent Generation Capability and Surface-Enhanced Raman Scattering Properties.

In this work, Langmuir–Blodgett (LB) composite thin films were successfully prepared using black phosphorus nanosheets (BPNS) and dye molecules. Black phosphorus (BP) was first exfoliated in isopropanol solution to form BPNS, and then, BPNS were modified with 4-azidobenzoic acid (Az-BPNS) to improve their stability. The characterization results showed that the synthesized Az-BPNS-dye LB films have a uniform and ordered structure. In addition, the synthesized Az-BPNS-dye LB films exhibit excellent photoelectrochemical performance, and Az-BPNS-methylene blue (MB) produces higher photocurrent compared to Az-BPNS-Neutral red (NR) films. The current work shows an effective way to prepare functionalized BP-based materials and provide evidence for their application in optoelectronic devices.

Wafer-scale SERS metallic nanotube arrays with highly ordered periodicity

The development of surface-enhanced Raman scattering (SERS) substrates has been hampered by difficulties in scaling up fabrication and an inability to obtain meaningful, statistical measurements of nanostructures, due to the effects of molecular adsorption. This paper reports on the wafer-scale fabrication of ultrahigh sensitivity SERS substrates using metallic glass nanotube arrays with highly ordered periodicity. Systematic micro-Raman spectroscopic analysis revealed that the fabricated array could function as a SERS-active substrate with crystal violet (CV) and folic acid as analytes (detection limit of 10−11 M and enhancement factor of 4.21 × 106 for CV). This work was the first to fabricate wafer-scale metallic nanotube arrays with SERS properties, which represents an important step toward realizing the large-scale fabrication of ultrasensitive SERS-active materials.

Comparison of Surface-Enhanced Raman Scattering Properties of Serum and Urine for the Detection of Chronic Kidney Disease in Patients.

Chronic kidney disease (CKD) affects more than 10% of the global population and is associated with significant morbidity and mortality. In most cases, this disease is developed silently, and it can progress to the end-stage renal failure. Therefore, early detection becomes critical for initiating effective interventions. Routine diagnosis of CKD requires both blood test and urinalyses in a clinical laboratory, which are time-consuming and have low sensitivity and specificity. Surface-enhanced Raman scattering (SERS) is an emerging method for rapidly assessing kidney function or injury. This study was designed to compare the differences between the SERS properties of the serum and urine for easy and simple detection of CKD. Enrolled for this study were 126 CKD patients (Stages 2–5) and 97 healthy individuals. SERS spectra of both the serum and urine samples were acquired using a Raman spectrometer (785 nm excitation). The correlation of chemical parameters of kidney function with the spectra was examined using prinicpal component analysis (PCA) combined with linear discriminant analysis (LDA) and partial least squares (PLS) analysis. Here, we showed that CKD was discriminated from non-CKD controls using PCA–LDA with a sensitivity of 74.6% and a specificity of 93.8% for the serum spectra, and 78.0% and 86.0 % for the urine spectra. The integration area under the receiver operating characteristic curve was 0.937 ± 0.015 (p < 0.0001) for the serum and 0.886 ± 0.025 (p < 0.0001) for the urine. The different stages of CKD were separated with the accuracy of 78.0% and 75.4% by the serum and urine spectra, respectively. PLS prediction (R2) of the serum spectra was 0.8540 for the serum urea (p < 0.001), 0.8536 for the serum creatinine (p < 0.001), 0.7500 for the estimated glomerular filtration rate (eGFR) (p < 0.001), whereas the prediction (R2) of urine spectra was 0.7335 for the urine urea (p < 0.001), 0.7901 for the urine creatinine (p < 0.001), 0.4644 for the eGFR (p < 0.001) and 0.6579 for the urine microalbumin (p < 0.001). In conclusion, the accuracy of associations between SERS findings of the serum and urine samples with clinical conclusions of CKD diagnosis in this limited number of patients is similar, suggesting that SERS may be used as a rapid and easy-to-use method for early screening of CKD, which however needs further evaluation in a large cohort study.

Silver microspheres aggregation-induced Raman enhanced scattering used for rapid detection of carbendazim in Chinese tea

Due to the excessive use of fungicides, pesticide residues have become a growing concern in recent years. Herein, we demonstrated an easy-prepared and low-cost surface enhanced Raman Scattering (SERS) chip composed of 3D silver microspheres (AgMSs) pattern for the quantitative testing of carbendazim in Chinese tea. Compared with the common monolayer SERS substrate, the 3D patterns formed by self-assembly AgMSs with fine nanostructure can offer much more aggregation-induced hotspots and generate strong 3D synergetic effects. Furthermore, when the thickness of the 3D pattern exceeded 6 μm, we replaced the conductive supporting coatings using the glass slides to reduce the cost without any impact on SERS properties. The prepared 3D chips achieved the determination of carbendazim within the linear range of 0.1–10 mg/L and the detection limit of 0.01 mg/L. It is simple and sensitive enough for the detection of most pesticide residues or other harmful organic molecules in our food or environment.