Surface-enhanced Raman Spectroscopy Study Research Articles

In situ surface-enhanced Raman spectroscopy study of interfacial catalytic reaction of bifunctional metal nanoparticles

In situ surface-enhanced Raman spectroscopy study of interfacial catalytic reaction of bifunctional metal nanoparticles

Determination of ammonia nitrogen by surface-enhanced Raman spectroscopy and DFT studies

Ammonia nitrogen is one of the most important indicators for evaluating the quality of water bodies. It is very difficult to determine ammonia nitrogen directly by Surface-enhanced Raman spectroscopy (SERS) in practice. In order to realize SERS determination of ammonia nitrogen, in this paper, SERS combined with density functional theory (DFT) was used to investigate why ammonia nitrogen needs to be derivatized to hexamethylenetetramine (HMTA) and why HMTA can be determined using SERS. The molecular electrostatic potential (MEP) results exhibit that there was no adsorption site on the surface of ammonia nitrogen, whereas its derivate HMTA had four available adsorption sites. This provides a basic guarantee for the SERS detection of HMTA. The molecular adsorption state of HMTA on the gold nanoparticles surface was concluded from the binding energies, the bond length, and the Raman activity spectra. Among them, the HMTA-Au4 complex has the lowest bond energy (−586.873 Kcal/mol) and the shortest bond length (2.161 Å), which is the most stable state and its Raman activity spectrum is the closest to the experimental data. Calculations results of frontier molecular orbital (FMO) demonstrate that the energy gap of HMTA and HMTA-Au4 complex are 0.30258 eV and 0.10947 eV, respectively, with a really obvious difference between them, which indicates that the HMAT-Au4 complex possessed higher chemical reactivity. In addition, charge transfer phenomenon on the MEP of HMTA-Au4 complex was deduced due to the change in the symmetry of its charge distribution, which can be explained the mechanism of chemical enhancement in the detection of HMTA by SERS. The selective enhancement at 1048 cm−1 peaks in theoretical spectrum and at 1044 peaks cm−1 in experimental spectrum provided theoretical and practical basis for indirect determination of ammonia nitrogen by SERS. The obtained results will help to better understand the reasons why some components are difficult to be directly determined by SERS, and why these components need to be derivatized. It provides a new method for components that are difficult to detect by SERS.

Surface Enhanced Raman Spectroscopy Studies on the “Hot Spot” Localized Area from Free Collision Behavior of Gold Nanoparticle-Gold Single Crystal Microplate

Surface Enhanced Raman Spectroscopy Studies on the “Hot Spot” Localized Area from Free Collision Behavior of Gold Nanoparticle-Gold Single Crystal Microplate

Ammonia Toxicity and Associated Protein Oxidation: A Single-Cell Surface Enhanced Raman Spectroscopy Study.

Ammonia (NH3) is a commonly used industrial chemical to which exposure at high concentrations can result in severe skin damage. Moreover, high levels of ammonia in the human body can lead to hyperammonemia conditions and enhanced cancer metabolism. In this work, the toxicity mechanism of NH3 has been studied against human dermal fibroblast (HDF) cells using surface-enhanced Raman spectroscopy (SERS). For this purpose, gold nanoparticles of size 50 nm have been prepared and used as probes for Raman signal enhancement, after being internalized inside HDF cells. Following the exposure to ammonia, HDF cells showed a significant variation in the protein ternary structure's signals, demonstrating their denaturation and oxidation process, together with early signs of apoptosis. Meaningful changes were observed especially in the Raman vibrations of sulfur-containing amino acids (cysteine and methionine) together with aromatic residues. Fluorescence microscopy revealed the formation of reactive oxygen and nitrogen species in cells, which confirmed their stressed condition and to whom the causes of protein degradation can be attributed. These findings can provide new insights into the mechanism of ammonia toxicity and protein oxidation at a single-cell level, demonstrating the high potential of the SERS technique in investigating the cellular response to toxic compounds.

Electrochemical Surface-Enhanced Raman Spectroscopy (EC-SERS) Study of C3 Polyalcohols Oxidation Catalyzed by a Ag Roughened Electrode with Low Platinum Content

Electrochemical Surface-Enhanced Raman Spectroscopy (EC-SERS) Study of C3 Polyalcohols Oxidation Catalyzed by a Ag Roughened Electrode with Low Platinum Content

Picosecond Bessel Beam Fabricated Pure, Gold-Coated Silver Nanostructures for Trace-Level Sensing of Multiple Explosives and Hazardous Molecules.

A zeroth-order, non-diffracting Bessel beam, generated by picosecond laser pulses (1064 nm, 10 Hz, 30 ps) through an axicon, was utilized to perform pulse energy-dependent (12 mJ, 16 mJ, 20 mJ, 24 mJ) laser ablation of silver (Ag) substrates in air. The fabrication resulted in finger-like Ag nanostructures (NSs) in the sub-200 nm domain and obtained structures were characterized using the FESEM and AFM techniques. Subsequently, we employed those Ag NSs in surface-enhanced Raman spectroscopy (SERS) studies achieving promising sensing results towards trace-level detection of six different hazardous materials (explosive molecules of picric acid (PA) and ammonium nitrate (AN), a pesticide thiram (TH) and the dye molecules of Methylene Blue (MB), Malachite Green (MG), and Nile Blue (NB)) along with a biomolecule (hen egg white lysozyme (HEWL)). The remarkably superior plasmonic behaviour exhibited by the AgNS corresponding to 16 mJ pulse ablation energy was further explored. To accomplish a real-time application-oriented understanding, time-dependent studies were performed utilizing the AgNS prepared with 16 mJ and TH molecule by collecting the SERS data periodically for up to 120 days. The coated AgNSs were prepared with optimized gold (Au) deposition, accomplishing a much lower trace detection in the case of thiram (~50 pM compared to ~50 nM achieved prior to the coating) as well as superior EF up to ~108 (~106 before Au coating). Additionally, these substrates have demonstrated superior stability compared to those obtained before Au coating.

In situ surface enhanced Raman spectroscopy study of electrode-polyelectrolyte interfaces.

As polyelectrolytes play a more and more important role in electrochemical fields, further understanding of the electrode-polyelectrolyte interface is in high demand. Surface-enhanced Raman spectroscopy (SERS) is utilized widely in electrode-solution interface research due to its ultra-high sensitivity, but is still rarely in the study of the electrode-polyelectrolyte interface due to difficulties in constructing appropriate electrochemical in situ devices. Additionally, the reported electrochemical in situ Raman works on the electrode-polyelectrolyte interface have a common problem of the coexistence of electrode-solution interfaces and electrode-polyelectrolyte interfaces. Here, we used screen printing electrodes (SPE) with a compact planar three-electrode structure to carry out a new electrochemical in situ SERS test method, which was suitable for the study of the electrode-polyelectrolyte interface. Polyelectrolyte membranes can be conveniently and closely coated on the SPE's planar three electrodes to achieve isolated electrode-polyelectrolyte interfaces without electrode-solution interfaces coexisting. Strongly potential-dependent signals were obtained from the Pt-Nafion™ interface directly across the Nafion™ membrane, which verifies that this method is practical for the electrochemical in situ SERS study of the electrode-polyelectrolyte interface.

Surface-enhanced Raman spectroscopy and density functional theory study of thymine-1-acetic acid interaction with silver nanoparticles

Thymine-1-acetic acid (TAA) is a modified nucleobase often used to add thymine functionality to materials. This study reports the Raman band assignments for TAA by comparing its experimental and density functional theory (DFT) simulated Raman spectra. Further comparison of experimental surface-enhanced Raman spectroscopy (SERS) of TAA on silver nanoparticles (Ag NPs) with simulated spectra of various complexes of xAg+ (x = 1, 2, or 3) and TAA reveals its likely adsorption orientation on the Ag NPs. This is one of the few studies that has achieved reasonably accurate simulation of SERS by employing multiple unconnected Ag+ ions, which could represent a compromise between a single atom or ion on one hand and a computationally expensive cluster on the other.

Fabrication and Comparative Quantitative Analysis of Plasmonic-Polymer Nanocomposites as Optical Platforms.

Plasmonic-polymer nanocomposites can serve as a multifunctional platform for a wide range of applications such as biochemical sensing and photothermal treatments, where they synergistically benefit from the extraordinary optical properties of plasmonic nanoparticles (NPs) and biocompatible characteristics of biopolymers. The field translation of plasmonic-polymer nanocomposites requires design rules for scalable and reproducible fabrication with tunable and predictable optical properties and achieving the best performance. The optical properties of NPs and the optimal analytical performance of nanocomposites could be affected by many fabrication parameters, but a fundamental understanding of such parameters is still minimal. Herein, we systematically investigated the NP distribution and their optical properties in gold nanostar (GNS)-polymer nanocomposites as a function of GNS concentration, polymer identity, and the method of GNS incorporation into a polymer matrix. We performed a comprehensive analysis of the single-particle scattering spectra of GNS incorporated into agarose gel and chitosan hydrogels via embedding and surface deposition, using dark-field spectroscopy. While relative GNS concentration affects the GNS scattering property distribution in both polymer matrices, chemical interactions between a polymer matrix and GNS is the key determinant of the GNS stability and homogenous distribution in nanocomposites. When GNS are embedded in a polymer matrix and there are stronger chemical interactions between GNS and a polymer, significantly less aggregation and a more homogenous distribution of GNS, which leads to a larger percentage of GNS optical property preservation, were observed at all the concentrations. In a proof-of-concept surface-enhanced Raman spectroscopy (SERS) study, we observed that the SERS detection efficiency is dictated by the analyte accessibility of GNS, which is governed by the polymer matrix porosity, polymer-GNS interactions, and other polymer physical characteristics. This work presents the interplay between key fabrication parameters and foundational design parameters for more predictable and reliable fabrication of plasmonic-polymer nanocomposites as an optical platform.

Surface-enhanced Raman spectroscopy studies of orderly arranged silica nanospheres-synthesis, characterization and dye detection

Surface-enhanced Raman spectroscopy studies of orderly arranged silica nanospheres-synthesis, characterization and dye detection

Electrochemical and surface enhanced Raman spectroscopy study of Guanine as corrosion inhibitor for copper

Guanine inhibition of copper corrosion in 0.1 M HCl was characterized by electrochemical and weight loss experiments under hydrodynamic conditions as well as by Surface-enhanced Raman spectroscopy (SERS). Cyclic voltammetry and polarization measurements revealed that Guanine adsorption modifies copper surface, thus inhibiting its corrosion. Weight loss and electrochemical impedance experiments showed that Guanine has an inhibition efficiency (ξ) of ∼87 % and that its protection is maintained up to 333 K. SERS measurements revealed that neutral Guanine adsorbs on copper at a wide potential range, forming a Cu(I)Guanine complex at greater immersion times.

Surface-enhanced Raman Spectroscopy and Density Functional Theory Study of Glyphosate and Aminomethylphosphonic acid Using Silver Capped Silicon Nanopillars

Glyphosate (GP) is a broad-spectrum systemic herbicide which is used for killing a wide variety of harmful plants. Several recent studies indicate possible adverse health effects on humans. This work is focused on detection and adsorption studies of GP and its metabolite aminomethylphosphonic acid (AMPA) on silver-capped silicon nanopillars using surface-enhanced Raman spectroscopy (SERS). Density Functional Theory with the B3LYP functional was employed for the geometry optimization of ground state geometries and simulation of Raman and SERS spectra of the GP and AMPA. The theoretically calculated and experimentally observed vibrations of GP and AMPA free and attached to the Ag surface exhibited different Raman spectra revealing chemical interactions between the analysed molecules and the metal surface. DFT studies confirmed that the main Ag-GP interaction is with the oxygen from carboxylic and phosphate groups, andfor AMPA the main interaction is via a strong interaction between nitrogen from NH with the metal surface. In order to study the binding behavior, adsorption isotherm analysis between GP and AMPA on silver-capped silicon nanopillars (AgNPs) were performed. Finally, the obtained isotherms for GP and AMPA followed a negative cooperative binding mechanism.

Synthesis, characterization and surface enhanced Raman spectroscopy study of a new family of different substituted cruciform molecular systems deposited on gold nanoparticles

AbstractIn this work, the adsorption and orientation on gold nanoparticles (AuNps) of a new family of cruciform systems consisting of thiophene rings and imino groups were studied. The structural modification and its influence on the adsorbate‐substrate interaction were evaluated by UV–Vis spectroscopy and Surface Enhanced Raman Spectroscopy (SERS). The absence of SERS spectrum for (N,N′‐bis(4‐(trifluoromethyl)benzylidene)‐2,5‐di (thiophene‐2‐yl)‐1,4‐diaminobenzene) CFF shows that the inclusion of a trifluoromethyl group (‐CF3) on the benzylidene fragment limits the interaction of the CFF system with the gold substrate, in contrast, to that obtained for (N, N′‐dibenzylidene‐2,5‐di (thiophene‐2‐yl) ‐1,4‐diaminobenzene) 2‐CF and (N, N′‐bis (4‐methoxybenzylidene) ‐2,5‐di (thiophene‐2yl) ‐1,4‐diaminobenzene) CMF, where the adsorption took place preferentially through the thiophene rings, resulting in partial quinoidization. On the other hand, the interaction for compound (N, N′‐bis (4‐methylenepyridinyl) ‐2,5‐di (thiophene‐2‐yl) ‐1,4‐diaminobenzene) CPy with the surface was conducted by means of the pyridinic fragments. The systematic modification of the bifunctional cruciform systems, with groups of different nature, makes it possible to rationalize the structural aspects that directly influence the adsorbate‐substrate interaction and molecular orientation on gold substrates. These structural parameters are the basis to the development of stable molecular assemblies, which can act as basic building blocks in the manufacture of molecular switches.

Fabrication of highly stable platinum organosols over DNA-scaffolds for enriched catalytic and SERS applications.

The use of nanomaterials (NMs) in various applications via multidisciplinary approaches is highly necessary in this era. In this line, the impact of noble metals in organic media for both catalysis and surface-enhanced Raman spectroscopic (SERS) studies is most interesting and also has a wider scope in various fields. Nonetheless, the catalytic reduction of aromatic nitro compounds is difficult with poor solubility in aqueous media, and reduction also is less feasible in the absence of noble metal-based catalysts. Thus, the choice of noble metal-based catalysts for the catalytic reduction of nitro compounds in organic media is one of the emerging methods with high selectivity towards products. Moreover, the superior catalytic activity of Pt NPs provides a higher rate constant value with a low dielectric constant of organic solvents. Herein, for the first time, we synthesised highly stable metallic Pt nanoparticles (NPs) anchored on bio-scaffold deoxyribonucleic acid (DNA) for two different applications. The advantage of highly controlled nucleation of NPs over DNA in organic media results in a spherical morphology with a particle diameter of 2.47 ± 2.11 nm and 2.84 ± 1.14 nm. A stable colloidal solution of Pt NPs was prepared by a simple wet chemical sodium borohydride reduction method within 15 minutes from the start of the reaction. Two sets of Pt NPs were synthesised by varying the molar ratio of the concentration of DNA to PtCl4 concentration and were named Pt@DNA (0.05 M) and Pt@DNA (0.06 M), respectively. The prepared Pt@DNA was effectively studied for two potential applications such as the SERS studies and catalytic reduction of nitro compounds. In catalysis, a higher catalytic rate was observed in the case of 4-nitrophenol (4-NP) at a rate of 8.43 × 10-2 min-1. In the SERS study, the reduction of the interparticle distance to below 5 nm facilitates the creation of a large number of hot spots for probe detection. Here, we used 10-3 M methylene blue (MB) as a probe molecule, and the enhancement factor (EF) value was calculated at different concentrations ranging from 10-3 M to 10-6 M. The highest enhancement factor (EF) value obtained was 2.91 × 105 for Pt@DNA (0.05 M). The as-synthesised stable Pt@DNA organosol can be exploited for other potential applications related to energy, sensor and medicinal fields in the near future.

Fabrication of high quality electrochemical SERS (EC-SERS) substrates using physical vapour deposition.

Screen-printed electrodes (SPEs) are an efficient and inexpensive substrate for electrochemical surface-enhanced Raman spectroscopy (EC-SERS) studies. Traditionally, the working electrode of the SPE is modified with either a colloidal paste of metal nanoparticles or an electrodeposited metallic film. These methods can be time-consuming and often produce non-uniform nanostructured films. Physical vapour deposition (PVD) is presented in this work as an efficient and effective alternative method for the production of SERS-active SPEs. SPEs coated with silver thin films via PVD show consistent and strong EC-SERS enhancement for the detection of two probe molecules, 4-aminothiophenol (p-ATP) and 5-(pyridine-4-yl)-1,3,4-oxadiazole-2-thiol (PYOT). The EC-SERS signal intensity for p-ATP and PYOT had coefficients of variation of 8.2% and 5.5%, respectively. More generally, these substrates show promise for reliable enhancement of molecules spanning diverse analytical applications.

Synthesis of Uniformly Sized Mesoporous Silver Films and Their SERS Application

Nanostructured metal films and particles have been recently exploited as substrates for surface-enhanced Raman spectroscopy (SERS) studies because their intrinsic properties lead to substantial Ram...

Ag@MoS2 Core-Shell Heterostructure as SERS Platform to Reveal the Hydrogen Evolution Active Sites of Single-Layer MoS2.

Understanding the reaction mechanism for the catalytic process is essential to the rational design and synthesis of highly efficient catalysts. MoS2 has been reported to be an efficient catalyst toward the electrochemical hydrogen evolution reaction (HER), but it still lacks direct experimental evidence to reveal the mechanism for MoS2-catalyzed electrochemical HER process at the atomic level. In this work, we develop a wet-chemical synthetic method to prepare the single-layer MoS2-coated polyhedral Ag core-shell heterostructure (Ag@MoS2) with tunable sizes as efficient catalysts for the electrochemical HER. The Ag@MoS2 core-shell heterostructures are used as ideal platforms for the real-time surface-enhanced Raman spectroscopy (SERS) study owing to the strong electromagnetic field generated in the plasmonic Ag core. The in situ SERS results provide solid Raman spectroscopic evidence proving the S-H bonding formation on the MoS2 surface during the HER process, suggesting that the S atom of MoS2 is the catalytic active site for the electrochemical HER. It paves the way on the design and synthesis of heterostructures for exploring their catalytic mechanism at atomic level based on the in situ SERS measurement.

Surface enhanced Raman spectroscopic studies on the adsorption behaviour of nitric oxide on a Ru covered Au nanoparticle film.

Nitric oxide (NO) is very interesting because of its effects on air pollution and especially biological systems. The adsorption behavior of NO molecules has fundamental importance with great technical challenges due to complex processes and species identification. Herein, the NO adsorption behavior on a Ru surface has been investigated using well-designed surface enhanced Raman spectroscopy (SERS) substrates. A Au nanoparticle monolayer film on ITO was employed as the electrode and Ru layers were electrochemically deposited. The internal SERS effect from the Au nanoparticles with high sensitivity and the metallic surfaces of Ru with practical application were integrated into a composite Au/Ru substrate. The molecular adsorption and dissociation of NO were observed simultaneously by SERS. A competitive relationship between adsorption and dissociation was observed at higher NO pressure, and the 3-fold and 2-fold bridge and top adsorption configurations appeared on the surface and were associated with different νNO vibrational frequencies. The results indicated that 3-fold bridge sites are preferred for dissociation over other structures. The dissociation of NO produced adsorbed atomic nitrogen and oxygen species to form Ru–N and Ru–O bonds, respectively. The dissociation process, especially for linear NO, was site dependent and blocked at higher pressure or coverage. Due to the change in adsorption energy and coverage, a conversion of the adsorption configuration from bridge to top was observed in the initial stage of NO adsorption, and this was followed by a mixture of bridge and top configurations of NO and dissociated species. A two-step dissociation mechanism and the steps of NO adsorption were proposed. The present study suggested that the SERS technique with appropriate attractive metal overlayers provided a significant and possibly even a valuable approach to explore adsorption behavior and kinetics at gas–solid interfaces.

Unveiling the size effect of Pt-on-Au nanostructures on CO and methanol electrooxidation by in situ electrochemical SERS.

In situ monitoring of electrocatalytic processes at solid-liquid interfaces is essential for the fundamental understanding of reaction mechanisms, yet quite challenging. Herein, Pt-on-Au nanocatalysts with a Au-core Pt-satellite superstructure have been fabricated. In such Pt-on-Au nanocatalysts, the Au cores can greatly amplify the Raman signals of the species adsorbed on Pt, allowing the in situ surface-enhanced Raman spectroscopy (SERS) study of the electrocatalytic reactions on Pt. Using the combination of an electrochemical method and in situ SERS, size effects of Pt on the catalytic performance of the core-satellite nanocomposites towards CO and methanol electrooxidation are revealed. It is found that such Pt-on-Au nanocomposites show improved activity and long-term stability for the electrooxidation of CO and methanol with a decrease in the Pt size. This work demonstrates an effective strategy to achieve the in situ monitoring of electrocatalytic processes and to simultaneously boost their catalytic performance towards electrooxidation.

Effect of Reaction Temperature on Shape Evolution of Palladium Nanoparticles and Their Cytotoxicity against A-549 Lung Cancer Cells.

Palladium nanoparticles (Pd NPs) of different shapes and sizes have been synthesized by reducing potassium tetrachloropalladinate(II) by l-ascorbic acid (AA) in an aqueous solution phase in the presence of an amphiphilic nonionic surfactant poly ethylene glycol (PEG) via a sonochemical method. Materials have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray soectrscopy (EDX), Fourier transform infrared (FTIR), surface-enhanced Raman spectroscopy (SERS), particle distribution, and zeta potential studies. Truncated octahedron/fivefold twinned pentagonal rods are formed at room temperature (RT) (25 °C) while hexagonal/trigonal plates are formed at 65 °C. XRD results show evolution of anisotropically grown, phase-pure, and well crystalline face-centered cubic Pd NPs at both temperatures. FTIR and SERS studies revealed adsorption of ascorbic acid (AA) and PEG at NP’s surface. Particle’s size distribution graph indicates formation of particles having wide size distribution while the zeta potential particle surface is negatively charged and stable. The truncated octahedron/fivefold twinned pentagonal rod-shaped Pd NPs, formed at RT, while thermally stable and kinetically controlled hexagonal/trigonal plate-like Pd NPs, evolved at higher temperature 65 °C. The obtained Pd NPs have a high surface area and narrow pore size distribution. To predict protein reactivity of the Pd cluster, docking has been done with DNA and lung cancer-effective proteins. The cytotoxicity of the Pd NPs has been screened on human lung cancer cells A-549 at 37 °C. The biological adaptability exhibited by Pd NPs has opened a pathway in biochemical applications.