Surface-enhanced Raman Scattering Study Research Articles

Theoretical Spectroscopic Study of Normal Raman and Charge Transfer Surface-Enhanced Raman Scattering (SERS) Spectra of the Adsorbed l- and d-Cysteine on the Chiral Au34 and Ag4@Au30 Nanoclusters: Chirality Discrimination.

In this work, the discrimination of the enantiomers of cysteine (l- and d-CYS) using the chiral Au34 and Ag4@Au30 clusters was theoretically investigated in the gas phase and water. Two modes were considered for the interaction of each enantiomer with the clusters (via only its S atom or its S atom and NH2 group, simultaneously). The interaction energy (Eint) and adsorption energy (Ead) for the complexation of each enantiomer with the clusters for each interaction mode were calculated. Considering the calculated interaction energies, the interaction of d-CYS with Au34 is stronger than that of l-CYS with the same cluster. Also, it was observed that the substitution of the Au4 core of the Au34 cluster with the Ag4 cluster caused the increase of the interaction energy of l-CYS with the Ag4@Au30 cluster compared to the Au34 cluster, while the reverse trend was observed for d-CYS. Quantum theory of atoms in molecules (QTAIM) analysis was employed to calculate the interaction paths and their related bond critical points (BCPs) between the CYS enantiomers and the clusters to explain the difference between the interaction energy of the enantiomers with the clusters. The IR, normal Raman (NR), and surface-enhanced Raman scattering (SERS) spectra of the enantiomers interacting with the Au34 and Ag4@Au30 clusters were calculated, and the discrimination between l-CYS and d-CYS using the calculated spectra was explained. It was found that the discrimination of the enantiomers based on their interaction with the clusters is controlled by the charge transfer between the enantiomers and the clusters.

Surface enhanced Raman spectroscopy for the characterization of the metabolites of the biodesulfurization of dibenzothiophene carried out by Tsukamurella paurometabola

Large amount of sulphur is released by the combustion of fossil fuels in the form of SoX which affects human health and leads to acid rain. To overcome this issue, it is essential to eliminate sulphur moieties from heterocyclic organo-sulphur compounds like Dibenzothiophene (DBT) present in the petrol. In this study Surface enhanced Raman scattering (SERS) spectroscopy is used to analyze the desulfurizing activity of Tsukamurella paurometabola bacterial strain. The most prominent SERS peaks observed at 791, 837, 944 and 1032 cm−1, associated to C–S stretching, are solely observed in dibenzothiophene and its metabolite-I (DBTS) but absent in 2-Hydroxybiphenyl (metabolite-II) and extraction sample of supernatant as a result of biodesulfurization. Moreover, the SERS peaks observed at 974 (characteristic peak of benzene ring) and 1015 cm−1 is associated to C–C ring breathing while 1642 and 1655 cm−1 assigned to CC bonds of aromatic ring. These peaks are only observed in 2-Hydroxybiphenyl (metabolite-II) and extraction sample of supernatant as a result of biodesulfurization. Notably, these peaks are absent in the Dibenzothiophene and its metabolite-I which indicate that aromatic ring is carrying sulfur in this fraction. Moreover, multivariate data analytical tools like principal component analysis (PCA) and PCA-loadings are applied to further differentiate between dibenzothiophene and its metabolites that are Dibenzothiophene sulphone (metabolite-I) and 2-Hydroxybiphenyl (metabolite-II).

Molecular Simulation Study of Surface-Enhanced Raman Scattering of Liquid Water.

We developed in our previous study [J. Chem. Phys., 2021, 155, 174118, J. Phys. Chem. A, 2022, 126, 4762] a classical electronic and molecular dynamics simulation method to describe the optical response of metal material in solution based on an atomistic model by incorporating the classical equation of motion for free electrons under an applied electric field. To show further usefulness of the method, in the present study, we apply it to surface-enhanced Raman scattering of liquid water to examine the signal enhancement of the solution system caused by plasmon resonance effects of a silver nanoparticle.

Surface-Enhanced Raman Scattering Studies of Au-Ag Bimetallic Nanoparticles with a Tunable Surface Plasmon Resonance Wavelength Synthesized by Picosecond Laser Irradiation

Here, we present a simple and green method of preparing Au-Ag bimetallic nanoparticles (NPs) with a tunable surface plasmon resonance (SPR) wavelength by using picosecond laser irradiation. Au-Ag alloy NPs have been produced by irradiating the solutions containing respective metallic salts in a polyvinyl alcohol (PVA) matrix using a picosecond laser in a single-step process. The SPR wavelength of the Au-Ag bimetallic NPs is observed to be shifted/changed with the Au-Ag concentration and the laser irradiation parameters. The Au-Ag NPs embedded in the PVA matrix are advantageous for Surface-Enhanced Raman scattering (SERS) applications. The estimated enhancement factors (EFs) were observed to vary as a function of conditions of the Au-Ag bimetallic alloy NPs synthesis and also on the concentration of Au at a fixed input fluence of irradiation. The SERS active platforms of Au-Ag bimetallic NPs showed EFs as high as of the order of 108 for Crystal Violet (CV) dye samples at nano molar concentrations. The present study demonstrates a simple, single-step, and green method that fabricates Au-Ag alloy-based nanocomposites suitable for SERS investigations with significantly higher orders of EFs.

Insights into Plasmon-Induced Dimerization of Rhodanine–A Surface-Enhanced Raman Scattering Study

Plasmon-mediated chemical reactions (PMCRs) have attracted considerable interest in recent times. The PMCR initiated by hot carriers is known to be influenced by the type of metals and the excitation wavelength. Herein, we have carried out the surface-enhanced Raman scattering (SERS) investigation of rhodanine (Rd), an important pharmacologically active heterocyclic compound, adsorbed on silver and gold nanoparticles (AgNP and AuNP) using 514.5 and 632.8 nm lasers. The prominent Raman band at 1566 cm-1 observed in the SERS spectra is attributed to the characteristic ν(C═C) stretching vibration of the Rd dimer and not of Rd tautomers. The chemical transformation of Rd to Rd dimer on metal surfaces is plausibly triggered by the indirect transfer of energetic hot electrons generated during the non-radiative decay of plasmon. The mechanism involved in the dimerization of Rd via the indirect transfer of hot electrons is also presented. The effect of wavelength on the dimerization of Rd is also observed on the AgNP surface, which indicates that the dimerization occurs more efficiently on the AgNP surface with excitation at 514.5 nm wavelength.

Conformational Selectivity of Merocyanine on Nanostructured Silver Films: Surface Enhanced Resonance Raman Scattering (SERRS) and Density Functional Theoretical (DFT) Study.

In this study, detailed structural and vibrational analysis of merocyanine has been investigated using Raman, surface enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS). The Raman, SERS and SERRS studies aided by density functional theoretical (DFT) calculations clearly established the prevalence of the trans- and cis-conformers of the protonated form of merocyanine (MCH+) in solid and acetonitrile solution. The binding characteristics of merocyanine adsorbed on nanostructured silver-coated films (SCFs) were investigated using excitation-dependent SERS, concentration-dependent SERRS and DFT studies. The conformers of merocyanine involved in the surface adsorption processes were recognized. The prominent marker bands observed at 1538 (ethylenic C=C stretch) and 1133 cm−1 (pyridinium C-N stretch) in the Raman spectrum of merocyanine in acetonitrile shifted to 1540 and 1126 cm−1, respectively on the nanostructured SCFs. The shift in the marker bands is associated with either the preferential binding of selective conformer or change in resonance equilibrium between the benzenoid and quinoid forms. The excitation wavelength dependent SERS spectrum infers that in addition to the major contribution from the electromagnetic enhancement, chemical (resonance) effect leads to the amplification of the 1540 cm−1 band. The concentration-dependent SERRS study showed maximum enhancement for the nanostructured SCFs functionalized with 1 μM concentration of merocyanine, indicative of monolayer coverage. For lower concentrations of merocyanine, the SERRS signal intensity reduced without any alteration in the peak positions. The SERRS study thus, revealed sub-nanomolar (0.1 nM) sensing of merocyanine using nanostructured SCFs with the analytical enhancement factor (AEF) of ∼ 1010 for the 1126 cm−1 and 1540 cm−1 Raman bands for MC concentration of 0.1 nM. In this study, combination of SERRS and DFT have clearly established the predominance of trans-MCH+ on the nanostructured silver surface with minor contribution from cis-MCH+, which remain exclusively bound to the surface via the phenoxyl ring O atom. This conformational surface selectivity of geometrical isomers of merocyanine using nanostructured surfaces can be further explored for energy efficient and economical separation of geometrical isomers.

Trace Cd2+ Ions Detection on the Flower-Like Ag@CuO Substrate.

CuO flower-like material (FM) was prepared via the facile hydrothermal method, and Ag nanoparticles were deposited on the CuO FM to obtain Ag@CuO composite. Rhodamine 6G (R6G) was used as the probe molecule on Ag@CuO FM substrate to study surface enhanced Raman scattering (SERS). It is discovered that it exhibited an excellent SERS performance with limit of detection of 3.58 × 10−16 M and enhancement factor (EF) of 3.99 × 1010. More importantly, we used it as a SERS substrate to detect cadmium ions and found that its limit of detection (LOD) reaches up to 2.6 × 10−8 M, which is lower than the highest allowable Cd2+ concentration in drinking water set by the World Health Organization (WHO) and Environmental Protection Agency (EPA). Therefore, the proposed composite can be applicable to the detection of Cd2+ in drinking water and in soil.

Synthesis and Single-Particle Surface-Enhanced Raman Scattering Study of Plasmonic Tripod Nanoframes with Y-Shaped Hot-Zones.

Herein, plasmonic metal tripod nanoframes with three-fold symmetry were synthesized in a high yield (∼83%), and their electric field distribution and single-particle surface-enhanced Raman scattering (SERS) were studied. We realized such complex frame morphology by synthesizing analogous tripod nanoframes through multiple transformations. The precise control of the Au growth pattern led to uniform tripod nanoframes embedded with circle or line-shaped hot spots. The linear-shaped nanogaps ("Y"-shaped hot-zone) of the frame structures can strongly and efficiently confine the electric field, allowing for strong SERS signals. Coupled with a high synthetic yield of the targeted frame structure, strong and uniform SERS signals were obtained inside the nanoframe gaps. Remarkably, quite reproducible SERS signals were obtained with these structures-the SERS enhancement factors with an average value of 7.9 × 107 with a distribution of enhancement factors from 2.2 × 107 to 2.2 × 108 for 45 measured individual particles.

Plasmonic Nanoslit Arrays Fabricated by Serial Bideposition: Optical and Surface-Enhanced Raman Scattering Study.

Recently, studies have been carried out to combine surface-enhanced Raman spectroscopy substrates that are based on either localized surface plasmon or surface plasmon polariton structures. By combining these two systems, the individual drawbacks of each can be overcome. However, the manufacturing methods involved so far are sophisticated, labor-intensive, expensive, and technically demanding. We propose a facile method for the fabrication of a flexible plasmonic nanoslit surface-enhanced Raman scattering (SERS) sensor. We utilized the pattern on periodic optical disks as an inexpensive substitute for printing the periodic pattern on polydimethylsiloxane with soft imprint lithography. The Ag nanoslits were fabricated by serial bideposition using the dynamic oblique angle deposition technique. The nanoslit structures were physically and optically characterized, and the experimental results were compared to the results of the numerical simulation: Monte Carlo and finite-difference time-domain simulation. The AgNS samples showed excellent SERS performance with an enhancement factor of ∼105 and a limit of detection of 5 × 10-7 g/mL for a Rhodamine 6G solution. Their biosensing capability was demonstrated by the sensing of bilirubin.

Direct Detection of Bacteria Using Positively Charged Ag/Au Bimetallic Nanoparticles: A Label-free Surface-Enhanced Raman Scattering Study Coupled with Multivariate Analysis

Rapid detection and discrimination of pathogenic bacteria for food safety, environmental pollution, medical diagnoses, and chemical and biological threats remains a considerable challenge. In the p...

Detection of Lignin Motifs with RuO2-DNA as an Active Catalyst via Surface-Enhanced Raman Scattering Studies

Biomass-derived lignin derivatives are significant biodegradable plant materials which produce a variety of value-added products by oxidation/oxidative cleavage methods. These value-added products constitute important materials for the sustainable production of biofuels. The ultralevel quantitative detection of feedstock carbonyls on metal surfaces is possible with surface-enhanced Raman spectroscopy (SERS) technique. Considering environmental friendly protocols for activation of molecular oxygen in both valorization methods of biomass, the corresponding SERS detection protocols are rare. Here, for the very first time, RuO2-DNA nanochains aggregate as an efficient catalyst for oxidation/oxidative cleavage of biomass-derived lignin mimics and their subsequent in-situ SERS detection. Notably, both reactions are carried out in aqueous medium. For the controlled oxidation study, veratryl alcohol and cinnamyl alcohol were used as lignin mimics, and the respective carbonyls were detected by the SERS method by activating molecular oxygen. Also, by changing the oxidant from molecular oxygen to peroxide, the respective acids were seen to be formed for veratryl alcohol. We extend this protocol to oxidative cleavage of lignin-derived olefins, and diols, such as cinnamyl alcohol and 1-phenyl-1,2-ethanediol, and corresponding acids were formed and detected by SERS technique. This oxidation protocol could also be scaled-up for large-scale synthesis and recyclability experiments to prove the robustness of the catalyst under green conditions.

Plasmon-Induced Dimerization of Thiazolidine-2,4-dione on Silver Nanoparticles: Revealed by Surface-Enhanced Raman Scattering Study

Surface-enhanced Raman scattering (SERS) study carried on thiazolidine-2,4-dione (TZD), a pharmacologically active heterocyclic compound, points to the presence of TZD dimer formed by plasmon-induced dimerization reaction of TZD on the surface of silver nanoparticles (Ag NP) at TZD concentrations of 10-3 M and above. The evidence for the presence of dimer was obtained from the appearance of a prominent band at 1566 cm-1 corresponding to the ν(C═C) band (a characteristic vibrational band observed for the Knoevenagel condensation reaction products) which is absent in the normal Raman scattering (NRS) spectra of TZD solid/solution. The observed spectrum compares well with the calculated spectrum of dimer obtained using density functional theory (DFT) calculations. The dimerization reaction is plausibly induced by the transfer of hot electrons generated by the nonradiative plasmon decay of Ag NP, and the proposed reaction mechanism is discussed. However, at lower concentrations (10-4-10-6 M), the characteristic dimer peak (1566 cm-1) is absent and the SERS spectra resemble more the NRS spectrum of TZD with a few changes. The spectral analysis supported by DFT calculations showed that TZD molecules undergo deprotonation and get adsorbed on the Ag NP surface as enolate forms. The proximity of TZD molecules on the surface of Ag NP is a necessary factor for the dimerization to occur. At lower concentrations, most molecules lie apart and reactions between molecules become less feasible, and they remain as monomers on the surface, while at higher concentrations the molecules are closer to each other on the Ag NP surface favoring the dimerization reaction to take place, leading to the formation of the dimer.

Fabrication of silver and silver-copper bimetal thin films using co-sputtering for SERS applications

The objective of this work is to tune the surface plasmon resonance (SPR) of thin silver and silver-copper bimetallic films into a strong and broad absorption in the red and near infrared regions for applications in Surface Enhanced Raman Spectroscopy. The SPR tuning was achieved by varying the composition of silver and copper in the films fabricated using magnetron co-sputtering method and also by annealing it under high vacuum condition. Atomic Force Microscope was used to study the film surface morphology and its growth with annealing temperatures. SPR exhibited by the films were directly studied using UV–Visible spectroscopy. Surface Enhanced Raman Scattering studies taken on Methylene Blue drop-casted on film surface shows a threefold increase in the enhancement factor of Ag–Cu films as compared to pure Ag sputtered films.

Surface Enhanced Raman Scattering Study of 1-H-2 (tolylazo) Imidazole (TaiH) Induced by Uncoupled Plasmon of Silver Nano Particles.

Raman and SER spectra of 1-H-2 (tolylazo) imidazole (Tai H) are reported for the first time. Monomolecular layer of TaiH is formed on silver nano particles (SNPs) at a concentration of 4.93×10-6 M in Ag-sol. TaiH molecules are adsorbed on to SNPs the through the imidazole N atom and undergo trans-to-cis dark isomerization as evidenced by the appearance of signature cis-peaks and the UV-Vis absorption spectra. Stable non-aggregated SNPs are resulted by the interaction of TaiH and the particle size is significantly reduced. DFT calculations based on single Ag-atom model are in excellent agreement with experimental observations.

Shape-selective catalysis and surface enhanced Raman scattering studies using Ag nanocubes, nanospheres and aggregated anisotropic nanostructures.

Three morphologies of silver nanoparticles (Ag NPs) such as nanocubes, aggregated anisotropic Ag NPs, and nanospheres were prepared using polystyrene sulfonate (PSS) and citrate as stabilizing agents utilizing a simple wet-chemical and microwave heating route respectively. Ag nanocubes were prepared within one min through microwave heating whereas anisotropic Ag NPs and spherical Ag NPs via 5 and 30min of normal stirring at room temperature (RT) respectively. The shape effect of three different morphologies of Ag NPs were examined in catalysis reaction and in surface enhanced Raman scattering (SERS) studies. For catalysis experiments, reduction of various nitroaromatics was done taking excess NaBH4 in presence of those morphologically different Ag NPs as catalyst and the corresponding catalytic activity is ordered as: Ag nanospheres>aggregated anisotropic Ag NPs>Ag nanocubes. The highest catalytic rate of ∼1.34×10-1min-1 was observed with citrate capped Ag nanospheres. SERS study was done taking methylene blue (MB) as the Raman probe where a highest enhancement factor (EF) of ∼1.05×107 was observed with Ag nanospheres and the order of EF values is as follows: Ag nanospheres>Ag nanocubes>aggregated anisotropic Ag NPs. The highest catalytic and SERS activity of citrate stabilized spherical Ag NPs are attributed due to the fast electron transfer in catalysis and creation of more number of surface active 'hot spots' in SERS studies. In future, the overall process we highlighted here might found potential application for the preparation of other varieties of nanomaterials applicable to catalysis reaction and in SERS-based trace analysis of various biologically important molecules and fine chemicals.

Study of Surface-Enhanced Raman Scattering of Plasmonic Coupled Biomolecule: Role of Multi-Layered Nanosphere

In this communication, we study the surface enhanced Raman scattering (SERS) by a molecule which is adsorbed on a trilayer (Ag@SiO2@Ag) spherical shaped metallic nanostructure. We have studied the plasmonic signature of the trilayer nanostructure under quasi-static approximation. The plasmonic response of trilayer nanostructures is analysed in terms of surface plasmon resonances and extinction efficiency which is a function of size, shape of core-shell material and thickness polarisability. The polarisability of trilayer nanostructure has been derived using T-matrix method and coupled it with the Gersten-Nitzan model to study the Raman enhancement factor. The Raman enhancement factor (R) has been studied under the influence of several parameters such as core-shell material, thickness, molecule distance and the surrounding media. The model developed here suggests strong relative amplification of the Raman gain of biomolecule adsorbed on the surface of the nanogeometry. The trilayer metal nanostructure exhibits three plasmon resonance peaks in UV to visible range (Raman spectroscopy range) which helps in detection of biological molecules into three different regimes. We have also compared the Raman enhancement factor for trilayer, bilayer and single metal nanosphere and it was observed that the magnitude of Raman gain factor, number of resonant peaks and its spectral bandwidth are different for different geometries.

Quantitative detection of codeine in human plasma using surface-enhanced Raman scattering via adaptation of the isotopic labelling principle

In this study surface enhanced Raman scattering (SERS) combined with the isotopic labelling (IL) principle has been used for the quantification of codeine spiked into both water and human plasma. Multivariate statistical approaches were employed for the analysis of these SERS spectral data, particularly partial least squares regression (PLSR) which was used to generate models using the full SERS spectral data for quantification of codeine with, and without, an internal isotopic labelled standard. The PLSR models provided accurate codeine quantification in water and human plasma with high prediction accuracy (Q2). In addition, the employment of codeine-d6 as the internal standard further improved the accuracy of the model, by increasing the Q2 from 0.89 to 0.94 and decreasing the low root-mean-square error of predictions (RMSEP) from 11.36 to 8.44. Using the peak area at 1281 cm-1 assigned to C-N stretching, C-H wagging and ring breathing, the limit of detection was calculated in both water and human plasma to be 0.7 μM (209.55 ng mL-1) and 1.39 μM (416.12 ng mL-1), respectively. Due to a lack of definitive codeine vibrational assignments, density functional theory (DFT) calculations have also been used to assign the spectral bands with their corresponding vibrational modes, which were in excellent agreement with our experimental Raman and SERS findings. Thus, we have successfully demonstrated the application of SERS with isotope labelling for the absolute quantification of codeine in human plasma for the first time with a high degree of accuracy and reproducibility. The use of the IL principle which employs an isotopolog (that is to say, a molecule which is only different by the substitution of atoms by isotopes) improves quantification and reproducibility because the competition of the codeine and codeine-d6 for the metal surface used for SERS is equal and this will offset any difference in the number of particles under analysis or any fluctuations in laser fluence. It is our belief that this may open up new exciting opportunities for testing SERS in real-world samples and applications which would be an area of potential future studies.

Design of Cu2O-Au composite microstructures for surface-enhanced Raman scattering study

Octahedral Cu2O-Au composite microstructures (CMSs) were synthesized with a facile in situ method and were attempted as surface-enhanced Raman scattering (SERS) substrates. The density of the Au nanoparticles (NPs) on the surface of the octahedral Cu2O microcrystals can be controlled by tuning the concentration of the gold precursor, which can further influence the SERS activity of the Cu2O-Au CMSs system. The CMSs system exhibited a charge transfer from Au to Cu2O. Furthermore, metallic NPs deposited on the semiconductor material formed a local electromagnetic field, which altered the interfacial charge distribution. The SERS signal enhancement from the Cu2O-Au CMSs system is attributed to a combination of electromagnetic and chemical enhancement mechanisms occurring simultaneously at the semiconductor-metal interface. Overall, the proposed CMSs system will provide a new model for SERS study and application.

High-Resolution Distance Dependence Study of Surface-Enhanced Raman Scattering Enabled by Atomic Layer Deposition.

We present a high-resolution distance dependence study of surface-enhanced Raman scattering (SERS) enabled by atomic layer deposition (ALD) at 55 and 100 °C. ALD is used to deposit monolayers of Al2O3 on bare silver film over nanospheres (AgFONs) and AgFONs functionalized with self-assembled monolayers. Operando SERS is used to measure the intensities of the Al-CH3 and C-H stretches from trimethylaluminum (TMA) as a function of distance from the AgFON surface. This study clearly demonstrates that SERS on AgFON substrates displays both a short- and long-range nanometer scale distance dependence. Excellent agreement is obtained between these experiments and theory that incorporates both short-range and long-range terms. This is a high-resolution operando SERS distance dependence study performed in one integrated experiment using ALD Al2O3 as the spacer layer and Raman label simultaneously. The long-range SERS distance dependence should make it possible to detect chemisorbed surface species located as far as ∼3 nm from the AgFON substrate and will provide new insight into the surface chemistry of ALD and catalytic reactions.

Surface enhanced fluorescence from corroles and SERS studies of explosives using copper nanostructures

We report the deployment of complex copper nanoparticles (NPs) and nanostructures (NSs), fabricated in a single step by ultrafast laser ablation of copper (Cu) in corroles/chloroform solutions, for surface enhanced fluorescence and surface enhanced Raman scattering studies (SERS). The characterization was performed by TEM, SAED, UV–visible absorption, and SEM techniques. Florescence enhancement of five orders in magnitude was obtained from corroles conjugated to Cu complex NPs. Cu NSs were utilized to record the SERS spectra of adsorbed Rhodamine 6G and explosive molecules of 5-amino-3-nitro-1,2,4-triazole and 1,1-diamino-2,2-dinitroethene. The estimated enhancement factors were in the range of 106–108.