Surface Enhanced Raman Spectroscopy Effect Research Articles

Direct observation and identification of nanoplastics in ocean water.

Millions of tons of plastics enter the oceans yearly, and they can be fragmented by ultraviolet and mechanical means into nanoplastics. Here, we report the direct observation of nanoplastics in global ocean water leveraging a unique shrinking surface bubble deposition (SSBD) technique. SSBD involves optically heating plasmonic nanoparticles to form a surface bubble and leveraging the Marangoni flow to concentrate suspended nanoplastics onto the surface, allowing direct visualization using electron microscopy. With the plasmonic nanoparticles co-deposited in SSBD, the surface-enhanced Raman spectroscopy effect is enabled for direct chemical identification of trace amounts of nanoplastics. In the water samples from two oceans, we observed nanoplastics made of nylon, polystyrene, and polyethylene terephthalate-all common in daily consumables. The plastic particles have diverse morphologies, such as nanofibers, nanoflakes, and ball-stick nanostructures. These nanoplastics may profoundly affect marine organisms, and our results can provide critical information for appropriately designing their toxicity studies.

Surface enhanced Raman spectroscopy effect and acicular growth of copper structures on Titania-Silica fibers

The development of copper nanomaterials with dendritic shapes or hedgehog morphologies is of interest due to their optical, electrical, and catalytic properties; and their applications in catalysis and surface enhanced Raman spectroscopy (SERS). Placing the particles on a ceramic matrix gives them support and the properties of both materials is benefit. In this research, a matrix of TiO2SiO2 ceramic fibers doped with copper microstructures was developed, to take advantage of the synergistic effect of both materials, and their ability to amplify signals in Raman spectroscopy was evaluated. Sol-gel and electrospinning techniques were used to obtain the ceramic matrix, and electrodeposition to obtain the copper structures. Characterization by infrared spectroscopy and X-ray diffraction allowed the identification of copper species such as CuO, Cu2O, and Cu(OH)2. In addition, the characterization with scanning electron microscopy allowed to identify morphologies on the fibers of spheres, dendrites, and needles, belonging to copper species. The materials presented SERS amplification factors of 20.23 and 9.51 for TiO2SiO2 fibers and TiO2SiO2Cu doped by 0.75 min respectively, for the 1373 cm−1 band of a 1 × 10−4 M violet crystal solution.

Quaternary-Ammonium-Modulated Surface-Enhanced Raman Spectroscopy Effect: Discovery, Mechanism, and Application for Highly Sensitive In Vitro Sensing of Acetylcholine.

Quaternary ammonium (QA) plays multiple roles in biological functions, whose dysregulation may result in multiple diseases. However, how to efficiently detect QA-based materials such as acetylcholine (ACh) still remains a great challenge, especially in complex biological environments. Here, a new effect [called quaternary-ammonium-modulated surface-enhanced Raman spectroscopy (QAM-SERS) effect] is discovered, showing that the existence of QA will modulate the intensity of SERS signals in a concentration-dependent manner. When the QAM-SERS effect is used, a new method is easily developed for in vitro detection of ACh with an extremely high sensitivity and an ultrawide dynamic range. Particularly, the linear dynamic range can be freely tuned to adapt for various physiological samples. As a proof-of-concept experiment, the time-dependent secretion of ACh from PC12 cells was successfully monitored using the QAM-SERS method, which were under either the stimulation of potassium ions or the incubation of drugs. The discovery of the QAM-SERS effect provides an easy and universal strategy for detecting ACh as well as other QA-contained molecules, which can also inspire new insights into the roles that QA could play in biology and chemistry.

Engineering of flexible granular Au nanocap ordered array and its surface enhanced Raman spectroscopy effect

Surface enhanced Raman spectroscopy (SERS) is a new and developing analytical technology in chemical and biological detection. However, traditional hard SERS substrates are struggling to meet the growing demand for flexible devices. In this work, we introduce a simple, cost-effective and large scale preparation route to form a flexible Au nanocap (AuNC) ordered array as SERS substrates via reactive ion etching (RIE) method and then Au deposition. We find RIE is an excellent method for nanoroughening the surface of polystyrene (PS) spheres. Such flexible SERS substrates exhibit high sensitivity and uniformity for detecting organic molecules. The finite-difference time-domain simulation results revealed that a strong electric field coupling effect existed not only in the gap site between the Au nanoparticles (AuNPs), but also in the connection position between the AuNCs and the single AuNP. This study not only offers a novel way for nanoroughening of PS spheres, but also acquires flexible and cheap SERS substrates for quick and sensitive detection of organic molecules.

Water Droplet Self-Assembly to Au Nanoporous Films with Special Light Trapping and Surface Electromagnetic Field Enhancement.

Gold nano "breath figure" films are for the first time reported and their function as ideal systems for plasmonics demonstrated. Metal nano-breath figure substrates are metal thin films containing nanohole arrays supported on a solid substrate. Au nanohole arrays are prepared from the dynamic breath figure phenomenon, in which the pore formation is controlled to provide holes smaller than 100 nm. Au layer is deposited on polymer substrates containing breath figure topology. The breath figure topology can be fully translated to the Au layer. The nanofabrication process is completed within few minutes. A simplified preparation process but very impressive light trapping and surface electromagnetic field enhancement are related to the Au breath figure films obtained in this work. The porous films demonstrated higher absorbance in the region of 500-1100 nm than nonporous Au films. In the case of 10 nm Au film, the plasmon absorbance becomes more intense than the electronic band absorbance. The electromagnetic enhancement is proved by surface enhanced Raman spectroscopy effect, which is found to be very close to the maximum possible value predicted for nonresonant species.

Effect of surface potential and charge transfer mechanism in reduced graphene oxide and magnetic nanocomposites

In this paper, the charge transfer mechanism in hydrothermally synthesized cobalt oxide/reduced graphene oxide (Co3O4/RGO) nanocomposites has been established. Scanning and transmission electron microscopy results expose the decoration of Co3O4 nanoparticles on GO sheets. Magnetic response of nanocomposites was confirmed from superconducting quantum interference device magnetometer measurement. Raman spectroscopy investigated optical properties of these nanocomposites. The Raman spectra of Co3O4/RGO nanocomposites shows the enhancement of D and G bands which are associated with GO due to the Surface-enhanced Raman spectroscopy effect and blue shift. Increase in the full-width half-maximum value as well as upshift in D and G peaks are strong signals of association of charge transfer process between GO sheets and decorated Co3O4 nanoparticles. The effect of charge transfer process is measured in the expression of shifting of Fermi energy level of Co3O4/RGO nanocomposites. Charge transfer is correlated with observed Raman shift and scanning Kelvin probe microscopy. XRD spectra of Co3O4/RGO confirm the polycrystalline nature of Co3O4 nanoparticles.

In situ surface-enhanced Raman spectroscopy effect in zeolite due to Ag2Se quantum dots

This study shows the presence of surface-enhanced Raman spectroscopy (SERS) effect caused by Ag2Se quantum dots embedded in the zeolite matrix. The quantum dots that were synthesised and stabilised in the matrix of F9-NaX zeolite show a size of 5 nm and a quasi-spherical morphology. The calculated interplanar distances confirm the presence of quantum dots in cubic phase Im-m. We suppose that the in situ SERS effect in the material is caused by chemical-enhancement mechanism (CEM). The density functional theory (DFT) is undertaken to corroborate our hypothesis. The structure H8Si8Al8O12 represents the zeolite cavity unit, and small clusters of (Ag2Se) n represent the quantum dots. Both structures interact in the cavity to obtain the local minimum of the potential energy surface, leading to new molecular orbitals. After the analysis of the predicted Raman spectrum, the Raman bands increase significantly, agreeing with the experimental results at low wavenumbers in F9-NaX zeolite.

Combined Photothermal and Surface-Enhanced Raman Spectroscopy Effect from Spiky Noble Metal Nanoparticles Wrapped within Graphene-Polymer Layers: Using Layer-by-layer Modified Reduced Graphene Oxide as Reactive Precursors.

To fabricate functionally integrated hybrid nanoparticles holds high importance in biomedical applications and is still a challenging task. In this study, we report the first reduced graphene oxide (rGO)-nobel metal hybrid particles that present simultaneously the photothermal and surface-enhanced Raman spectroscopy (SERS) effect from the inorganic part and drug loading, dispersibility, and controllability features from LbL polyelectrolyte multilayers. The hybrid particles where spiky noble metal particles were wrapped within rGO-polyelectrolyte layers were prepared by a facile and controllable method. rGO template modified using polyethylenimine (PEI) and poly(acrylic acid) (PAA) via layer-by-layer technology served as the reactive precursors, and the morphologies of the particles could be facilely controlled via controlling the number of bilayers around the rGO template. The hybrid particle presented low cytotoxicity. After loading doxorubicin hydrochloride, the particles effectively induced cell death, and photothermal treatment further decreased cell viability. rGO-Ag hybrid particles could be prepared similarly. We expect the reported method provides an effective strategy to prepare rGO-noble metal hybrid nanoparticles that find potential biomedical applications.

Synthesis of porous gold nanoparticle/MoS2 nanocomposites based on redox reactions

We develop a facile method for preparing the porous gold nanoparticles (Au-NPs)/2H-form MoS2 nanocomposite that forms a unique 3-dimensional structure and shows a high surface enhanced Raman spectroscopy effect.

Adsorption of Rhodamine 6G on SiO2 and Ag@SiO2 Porous Solids: Coupling Thermodynamics and Raman Spectroscopy

The sensitive detection of small molecules analytes at very low concentrations is of great interest, notably in the medical and environmental fields. In this study, two porous solids, namely SiO2 (dpore ≈ 5 nm) and Ag@SiO2, were prepared. In the latter, the incorporation of Ag nanoparticles in the porous matrix was highlighted using different techniques. Around 0.25 wt % of nanoparticles were inserted with a mean diameter close to 3 nm. Then, the adsorption of rhodamine 6G (R6G) on these two materials was studied coupling thermodynamics and Raman spectroscopy. From a thermodynamic point of view, it was shown that whereas the adsorbed amounts of R6G (Nads) were not affected by the presence of Ag nanoparticles, the adsorption enthalpies in the case of Ag@SiO2 are doubled compared to those of SiO2, highlighting the strong interaction of R6G with the Ag nanoparticle surface. Furthermore, for Nads > 1 μmol g–1, it was evidenced that the Raman response of R6G, in terms of band positions and intensities, is directly related to the amounts of R6G adsorbed on the solid surface and not to the presence of Ag. This result highlights the preconcentration properties of porous solids. For Nads = 0.05 μmol g–1, the intensities of Raman bands that are detected, corresponding to bending modes of ethylamine groups, are enhanced in the case of Ag@SiO2 by a factor of roughly 10. This value corresponds to the order of magnitude generally assumed for the chemical enhancement mechanism of surface enhanced Raman spectroscopy effect. This result and the high values of integral enthalpies of adsorption determined for Ag@SiO2 highlight strong interactions between amine groups and the Ag surface.

Preparation of nanoparticles-modified silica monolith for on-column surface enhanced Raman spectroscopy

A novel silica monolith modified with Ag/Au nanoparticles was prepared for the on-column surface enhanced Raman spectroscopy (SERS). The bare monolithic silica column was prepared from in-situ co-condensation of tetraethoxysilane (TMOS) and methyl trimethoxysilane (MTMS) in the presence of polyethylene glycol (PEG) via a sol-gel process in the capillary, and was chemically modified with (3-mercaptopropyl) trimethoxysilane (MTPMS), followed by immobilization of Ag/Au nanoparticles. Transmission electron microscopy (TEM) and UV-Vis spectrometer were used to collect the TEM images and the extinction spectra of the nanoparticles colloid, respectively. Scanning electron microscope (SEM) was utilized to record the morphology of the silica monolith The authros used p-aminothiophenol (PATP) as a probing molecule, and the SERS effect was investigated on Au/Ag nanoparticle-modified silica monolith under the excitation line of 633 and 532 nm, respectively. It is concluded that nanoparticle-modified silica monoliths will have broad application to the on-site detection of food and water contaminants in the field.

Fabrication and optical properties of controlled Ag nanostructures for plasmonic applications

Noble metal nanoparticles exhibit unique plasmon resonances compared to bulk metal that depends on the nanoparticle size, shape, and interparticle distance. Towards this goal, the paper describes a simple and low-cost method for producing large area arrays of ordered silver nanoparticles with morphologies such as dots, rings, and bowls, based on the nanosphere lithography by combining evaporation and sputtering techniques. Pronounced, we demonstrate here a facile fabrication strategy that nanosphere monolayer could serve as a sacrificial mask access to generate silver nanobowl arrays. The experimental and simulated results show that the Ag nanodot arrays exhibit a satisfactory surface-enhanced Raman spectroscopy effect and adjustable frequency. These approaches will surely facilitate further exploration of metal nanostructures for applications in nanoscale optical sensors.

Increasing surface enhanced Raman spectroscopy effect of RNA and DNA components by changing the pH of silver colloidal suspensions

This work focused on establishing the parameters for enhancing the Raman signals of DNA and RNA constituents: nitrogenous bases, nucleosides and nucleotides, using metallic nanoparticles as surface enhanced Raman scattering substrates. Silver nanospheres were synthesized using sodium borohydride as a reducing agent and sodium citrate as a capping agent. The prepared nanoparticles had a surface plasmon band at ∼384 nm and an average size of 12 ± 3 nm. The nanoparticles’ surface charge was manipulated by changing the pH of the Ag colloidal suspensions in the range of 1–13. Low concentrations as 0.7 μM were detected under the experimental conditions. The optimum pH values were: 7 for adenine, 9 for AMP, 5 for adenosine, 7 for dAMP and 11 for deoxyadenosine.

Interaction of 2- and 4-Mercaptopyridine with Pentacyanoferrates and Gold Nanoparticles

2-Mercapto- and 4-mercaptopyridine (2- and 4MPy) react with the [Fe(CN)(5)(H(2)O)](3-) complex, forming the S-coordinated [Fe(CN)(5)(2MPy)](3-) and the N-coordinated [Fe(CN)(5)(4MPy)](3-) complexes. The rates of formation and dissociation of the [Fe(II)(CN)(5)(2MPy)](3-) complex were determined as k(f) = 294 dm(3) mol(-1) s(-1) and k(d) = 0.019 s(-1) by means of stopped-flow technique. The equilibrium constants for the iron(II) and -(III) species were calculated as K(f)(II) = 1.5 x 10(4) mol(-1) dm(3) and K(f)(III) = 1.3 x 10(6) mol(-1) dm(3), in comparison with 2.6 x 10(5) and 3.4 x 10(4) mol(-1) dm(3), respectively, for the 4MPy isomer. In the presence of gold nanoparticles, both 2- and 4MPy can displace the stabilizing citrate species, leading to substantial aggregation in aqueous solution, as deduced from the surface-enhanced Raman spectroscopy effect and from the decay of the 520-nm plasmon band accompanied by the rise of the characteristic exciton band at 650 nm. The [Fe(CN)(5)(4MPy)](3-) complex promotes strong stabilization of the gold nanoparticles by interacting through the S atom. On the other hand, the labile [Fe(CN)(5)(2MPy)](3-) complex induces aggregation, delivering the 2MPy ligand to the gold nanoparticles.

Interaction of pyridine with photoelectrons emitted at the silver/aqueous solution interface

Pyridine added to a solution containing scavengers of photoelectrons emitted from silver (N 2O, CO 2) causes a strong decrease in the measured photocurrent or even its complete suppression for concentrations of pyridine exceeding 0.1 M. Such behaviour, which remains in apparent contradiction to the effect of deposited pyridine on photoemission from silver in vacuum, is due to the fact that pyridine itself acts as an acceptor of the emitted photoelectrons. As the anion radical formed undergoes reoxidation (back electron transfer) at the silver surface, this process leads to a decrease in the net photocurrent which is dependent on the concentration ratio of the two competing acceptors (i.e. pyridine and N 2O). The observation that pyridine (adsorbed on silver and in solution) sustains a reversible electron transfer, along with the previous observation that photoemission from a roughened Ag electrode into an aqueous solution extends to at least 650 nm, provides a possible interpretation of the surface-enhanced Raman spectroscopy effect for pyridine, which involves both electromagnetic and charge-transfer mechanisms.