Raman Spectrum Intensity Research Articles

Surface-Enhanced Raman Spectroscopy Substrate Time Stability Improvement Using an External Oxygen Barrier Method.

The poor time stability of surface-enhanced Raman scattering (SERS) substrates greatly limits their application potential. Although core-shell structures are commonly used to enhance stability, their complex preparation processes, high costs, and susceptibility under acidic or alkaline conditions result in serious disadvantages for practical applications. Here, we propose a new method of external oxygen barrier to improve spectral stability, in which SERS substrates are stored in an oxygen-free environment. Controlled experiments are carried out under air and vacuum. Raman spectrum intensity is measured 11 times within six months for each group. Using the attenuation formula, the Raman spectrum intensity decay results of each SERS substrate over time are obtained. The effectiveness of the external oxygen barrier method is demonstrated through curve fitting using the corresponding function. The substrate spectral attenuation rates of the vacuum group and the argon group within six months are <20%, proving the effectiveness of the external oxygen barrier method.

2D BN-biphenylene: structure stability and properties tenability from a DFT perspective.

With state-of-the-art density functional theory and ab initio molecular dynamics, we explored the BN-analog of a recently synthesized 2D biphenylene sheet. Its dynamical, thermal, and mechanical stability has been confirmed with phonon spectrum calculations, ab initio molecular dynamics (AIMD), and Born criteria, and its synthesis feasibility has been ascertained in terms of cohesive energy. The phonon spectrum and AIMD results show all positive frequencies and negligible variations in structure (bond length), kinetic and total energy for 5 ps, respectively. Having found this stable BN-BPh, we have analyzed its electronic, mechanical, optical, and vibration properties. Electronic property results (density of states and band structure) show that the BN-equivalent of metallic BPh has a large band gap of 3.12 eV and 4.48 eV with the PBE and HSE06 DFT functionals, respectively, similar to the graphene BN-equivalent (hBN) with a band gap of 6.1 eV. The mechanical strength of BN-BPh is close to that of BPh with a difference of ∼15 N m-1 and ∼10 N m-1 along the x- and y-directions, and its Young's modulus indicates that BN-BPh is stiffer than BN-graphyne. The optical absorption coefficient of BN-BPh shows a first peak at 4.48 eV (3.12 eV) with the HSE06 (PBE) functional. Infrared and Raman spectrum intensity and irreducible representation are computed, and the first IR (Raman) peak is found at 1300 cm-1 (1000 cm-1) for BN-BPh. Finally, substitutions of external atoms such as P, Al, As, C, Li, Mg, S, and Si for B and N atoms in BN-BPh tune its electronic properties to semiconducting, semi-metallic, and even metallic. Considering its mechanical, optical, and band gap tunability, BN-BPh might be useful in electronic, optical, and spintronics devices, even in high-pressure environments.

Model Parameter Self-Correcting Fuzzy Proportional–Integral–Derivative Adaptive Control of the Integration Time of Raman Spectrometers

The control of the integration time of Raman spectrometer is a crucial factor for the acquisition quality of Raman spectrum. However, due to the coupling effect of linear and nonlinear factors such as the intensity of Raman scattering effect, acquisition noise, fluorescence effect, and spectrometer optical path, it is rather difficult to fast control the integration time, which influences the acquisition efficiency. In this article, aiming at the nonlinear automatic optimal control of the integration time, a model parameter self-correcting fuzzy proportional–integral–derivative adaptive (MPSC-FPIDA) control method is proposed. By constructing an initial parameter prediction model and the fuzzy PID controller, two processing stages, namely, Raman spectrum intensity detection and fuzzy PID iterative control, are carried out, with which the automatic calculation and optimal control of the integration time of the Raman spectrometer are achieved according to the set point of spectrum intensity or signal-to-noise ratio (SNR). By introducing a parameter self-correcting factor of the initial model, the adaptive correction of the parameters of the initial prediction model of Raman spectrometers with different optical laser wavelengths is realized, which ensures the universality of this method to spectrometers of different types. The experiment demonstrates that when it comes to acquisition of Raman spectrum for various samples, the method proposed in this article can accurately calculate the optimal integration time within 2–3 iterations and automatically adapt to the performance parameters of different Raman spectrometers, of which the control performance is as good as that of modeling spectrometers. This shows that the method features fast convergence speed, strong robustness, and versatility. In addition, compared with commonly used linear control methods, it can effectively suppress the coupling effect of linear and nonlinear factors, which improves the efficiency of spectrum acquisition and enhances the control performance by over 50% as well.

Raman detection system for in situ oxidation and ablation analysis in hypersonic wind tunnel

AbstractWe have developed a system for remote Raman spectra detection in hypersonic wind tunnel, which can be used in extreme environments such as ultra‐high temperature, high pressure, and complex airflow to measure in situ Raman spectra of ceramic matrix composites during oxidation, phase transformation or ablation. The designed system avoids stray light generated by windows and airflow through oblique incidence of excitation light. The time‐resolved method combined with pulsed laser and intensified charge‐coupled device (ICCD) was used to reduce the thermal emission background. An optical structure design based on fiber bundle is adopted to suppress the influence of aero‐optical effects and mechanical vibration on Raman spectrum acquisition. We demonstrated the feasibility of in situ Raman spectra detection in a Mach 5 combustion wind tunnel system. The design of anti‐interference prevents Raman spectra intensity from the influence of wind tunnel testing conditions.

Photo-induced Electron Emission of Nanostructured Carbon Thin Film Based Transmission Photocathodes at Different Electric Field

Very thin nanostructured carbon films were deposited on quartz substrate by reactive magnetron sputtering using graphite target and gas mixture of Ar and reactive gas N_2 or N_2+H_2. Film thicknesses were in the range of 20-25 nm. Rutherford backscattering spectrometry and Elastic recoil detection analytical method determined the concentration of elements in the films. Scanning electron microscopy scanned the surface morphology of carbon films. Raman spectroscopy was used for chemical structural properties determination of very thin carbon films. Raman spectra intensities were fitted with Gaussian peaks. The photo-induced (pulsed laser - 266 nm) electron emission properties of very thin nanostructured carbon films were investigated by the measurement of cathode bunch charge at different electric field and calculate quantum efficiency. The influence of different electric field on the photo-induced electron emission characteristics of prepared transmission photocathodes are discussed.

Prevalence of Microplastics in the Eastern Oyster Crassostrea virginica in the Chesapeake Bay: The Impact of Different Digestion Methods on Microplastic Properties.

This study aimed to determine the microplastic prevalence in eastern oysters (C. virginica) in three sites in the Chesapeake Bay in Virginia and optimize the digestion methods. The digestion results illustrate that the lowest recovery rate and digestion recovery were related to enzymatic, enzymatic + hydrogen peroxide (H2O2), and HCl 5% treatments, while the highest digestion recovery and recovery rate were observed in H2O2 and basic (KOH) treatments. Nitric acid digestion resulted in satisfying digestion recovery (100%), while no blue polyethylene microplastics were observed due to the poor recovery rate. In addition, nitric acid altered the color, changed the Raman spectrum intensity, and melted polypropylene (PP) and polyethylene terephthalate (PET). In order to determine the number of microplastics, 144 oysters with an approximately similar size and weight from three sites, including the James River, York River, and Eastern Shore, were evaluated. Fragments were the most abundant microplastics among the different microplastics, followed by fibers and beads, in the three sites. A significantly higher number of fragments were found in the James River, probably due to the greater amount of human activities. The number of microplastics per gram of oyster tissue was higher in the James River, with 7 MPs/g tissue, than in the York River and Eastern Shore, with 6.7 and 5.6 MPs/g tissue.

Plasmonic alloy nanochains assembled via dielectrophoresis for ultrasensitive SERS.

It is great challenge and interesting for researchers to fabricate substrates for enhanced Raman and sensor, and assemble some easy-to-synthesize metallic nanomaterials into controllable nanostructures with special morphologies and arrangements, via alternating current (AC) electric field. The Au-Ag alloy nanoparticles (Au-Ag alloy NPs) colloidal suspension with excellent dispersibility synthesized by wet chemical method, and the morphology of the assembly can be well controlled by regulating the frequency of the AC electric field. Au-Ag alloy nanochains array (Au-Ag ANCs) with dense plasmonic "hot spots" is formed when the AC electric field of 4Vpp-30kHz is applied, which is supported by the result of finite element method (FEM) numerical simulation. Experimental results demonstrate that Au-Ag ANCs show excellent SERS activity: Au-Ag ANCs can detect both Rhodamine 6G (Rh6G) and crystal violet (CV) in the magnitude order of 10-10 M, and the Raman peaks intensity and analyte concentration has a strong linear correlation (R2 is 0.99339 and 0.95916, respectively). Besides, the introduction of Au-Ag ANCs makes the Raman spectra intensity of thiram (a pesticide) with a concentration of 30 ppm on the surface of the blank ITO glass significantly enhanced, and it can detect thiram with a concentration as low as 0.03 ppm. In addition, Au-Ag ANCs substrate exhibits great uniformity and stability, so they have considerable application potential in the field of quantitative detection of trace substances.

(Invited) Combined Single-Molecule Raman and Conductance Spectroscopies

The nanoscale manipulation and characterization of individual molecules is necessary for understanding the intricacies of molecular structure which ultimately governs phenomena such as reaction mechanisms, catalysis, local effective temperatures, surface interactions, and charge transport phenomenon. Along these lines, the field of molecular-scale electronics has evolved tremendously in recent years: from the initial experiments claiming single-molecule conductance measurements to the development of robust and reproducible platforms that have begun providing a detailed understanding of the charge transport properties of these systems. It has now become possible to probe the chemical, structural, mechanical, and electrical properties of single-molecule devices to explore unique functional paradigms for applications. However, continued advances in in situ characterization of a molecular junction are needed to provide detailed information about the molecular configuration and its impact on the charge transport, reactions, and device behavior. Single-molecule conductance and Raman spectroscopies each provide unique perspectives into the behavior of molecular systems and reactions at the single-molecule level. In this talk we will discuss the development and implementation of system designed to simultaneously obtain conductance information and Raman spectra from a molecular junction to provide this information. This will include the development of a MEMS-based break junction system that allows facile integration with a Raman microscope to maximize the solid-angle and photon collection.This multi-dimensional information yields repeatable, self-consistent, verification of single-molecule resolution, and allows for detailed analysis of structural and configurational changes of the molecule in situ. We will discuss the correlation between single-molecule binding events and changes in Raman spectra (intensity, modes, etc.) and conductance to explore the possibility of obtaining single-molecule spectra from the molecule bound between two electrodes. We will further explore the utility of this system for in situ characterization of active single-molecule devices including electrically-active single-molecule switches and memory devices.

An approach for optimizing gold nanoparticles for possible medical applications, using correlative electron energy loss and Raman spectroscopies on electron beam lithographically fabricated arrays

Surface-enhanced Raman spectroscopy (SERS), as induced by noble metal nanoparticles, is used for medical applications. In this study, gold nanoparticle parameters such as size, shape, separation, substrate etc. are varied systematically using electron beam lithographic fabrication methods. The resultant Raman spectra intensities are correlated with the nanoparticle surface plasmon energies as determined by electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) at nanometer-scale resolution. It is found that the largest enhancement is achieved when the illuminating laser energy closely matches, or is slightly higher than, the surface plasmon energies. In general, nanoparticle size is a strong determinant factor, and higher intensities are generated by sharply defined features. This approach allows a procedure to identify the optimum combination of nanoparticle parameters and laser energy to generate the largest Raman signals, thus enabling detection, for instance, of smaller, early-stage cancer tumors.

Efficacy of Nanobubbles Alone or in Combination with Neutral Electrolyzed Water in Removing Escherichia coli O157:H7, Vibrio parahaemolyticus, and Listeria innocua Biofilms

Due to the relatively high tolerance and resistance to sanitizers, biofilms can persist in the environment resulting in cross-contamination. The overall goal of this study was to evaluate the impact of nanobubbles (NB) alone and in combination with neutral electrolyzed water (NEW) on different microbial biofilms including Escherichia coli O157:H7, Vibrio parahaemolyticus, and Listeria innocua on plastic and stainless steel (SS) coupons. NB alone completely removed V. parahaemolyticus biofilm on both plastic and SS coupons after 2 min. NB alone caused about a 1 to 3 log CFU/cm2 reduction of E. coli and L. innocua biofilms, while a complete reduction was observed only after combining NB with NEW. The antiadhesion results of NB-treated plastic and SS coupons showed lower bacterial adhesion to NB-treated surfaces indicating that NB can attach to the surface and reduce the surface tension and bacterial adhesion. Surface-enhanced Raman spectroscopy spectra (SERS) and mapping results revealed the ability of NB to remove the bacterial biofilms. Raman spectra intensity was reduced at bands associated with carbohydrates, protein, and DNA indicating extracellular polymeric substance (EPS) disruption. This study demonstrates that NB could be a viable technology for removing microbial biofilms from surfaces and enhancing the efficacy of conventional sanitizers.

Synthesis of High-Performance Photonic Crystal Film for SERS Applications via Drop-Coating Method

Silica nanospheres with a well-controlled particle size were prepared via a nucleation-to-growth synthesis process. A facile method is proposed for improving the self-assembly behavior of silica colloidal particles in droplet coatings by the simple controlling of the drying temperature. It is shown that a periodically arranged, opal-structured, photonic crystal film with a large area of approximately 4.0 cm2 can be prepared, even when the particle size is up to 840 nm. When the band gap of the silica photonic crystals falls in the visible-light region, the crystals exhibit distinct structural colors. Moreover, the wavelength of the reflected light increases with an increasing particle size of silica. When the photonic band gap overlaps the wavelength of the laser source, the overall Raman spectrum intensity is significantly enhanced. Accordingly, the proposed nucleation-to-growth process and drop-coating method provides a cheap and simple approach for the manufacture of uniform sized silica and surface-enhanced Raman scattering substrates, respectively.

Successful Synthesis of Graphene Aluminum Composite with Improved Microhardness

In this work we1 successfully prepared aluminum-graphene composite (0.2 wt%) after 6 hrs of successful ball milling. The ball milling experiments were conducted between 2 and 6 hrs. The microstructal and spectroscopic comparison of aluminium-graphene composites were studied by evaluating properties by characterizing via XRD, FESEM, TEM, Micro Raman and microhardness. The second order disorder peak (2D) was found grow with milling time. In the Raman spectra intensity of 2D addresses about exfoliation take place of graphene in the composite. 0.2 wt% added graphene shows higher hardness than aluminium. Sintering of composites were done at 600 0C. Separation of stacking of carbon layers was confirmed from improvement of D peak in the ball milled samples. Sheet type structure of graphene was shown in TEM study. XRD confirms composite formation.

Zircon and apatite as tools to monitor the evolution of fractionated I-type granites from the central Great Xing’an Range, NE China

It is widely accepted that granitic melts can be highly evolved, however, the effective records of this process are usually obscure, especially for the exsolution and evolution of volatiles. We present a comprehensive investigation on zircon and apatite from less to highly fractionated granites from the central Xing’an Range, NE China, in order to reveal the mineral records for the evolution processes of granitic melt. Petrographic, whole-rock and mineralogical geochemical investigations indicate that the three granites are co-magmatic and experienced different degrees of fractionation. The variations of zircon morphology, textures and geochemical compositions reflect the progressive evolution of granitic melts from volatile-undersaturated to oversaturated conditions. The significantly decreased Raman spectra intensities imply that the zircon crystals experienced increased radiation damages and hydrothermal alteration during the fractionation of granitic magma. Correspondingly, apatite textures transform from fluid-inclusion-free to fluid-inclusion-rich stage with increasing F/Cl ratios during the magmatic evolution, implying that the segregation of isolated fluid phase in the fractionating magma. Accordingly, we conclude that the textural and compositional evolution of zircon and apatite can be regarded as efficient tools for recording granitic magma evolution.

Development of biocompatible plasmonic thin films composed of noble metal nanoparticles embedded in a dielectric matrix to enhance Raman signals

This work focused on the production of nanocomposite thin films, composed of noble nanoparticles embedded in a dielectric matrix, to be tested as biocompatible plasmonic platforms for detection of molecules using Surface Enhance Raman Spectroscopy (SERS). Three different thin films systems were deposited by reactive DC magnetron sputtering, namely Au-Al2O3, Au-TiO2 and Ag-TiO2. The depositions were followed by a thermal treatment at different temperatures to promote the growth of the nanoparticles. Localized Surface Plasmon Resonance (LSPR) bands appeared already at 300 °C, related to the presence of Au nanoparticles, and at 500 °C in the case of Ag nanoparticles. Furthermore, at 700 °C, the Ag-TiO2 films showed a broadband optical response due to the formation of Ag clusters at the film's surface. The biological experiments showed that the presence of the thin films didn't affect the growth of C. albicans, which is very convenient if one needs to detect low concentrations of this microorganism using SERS platforms. As for the SERS measurements, an enhancement of R6G Raman spectra intensity was clearly perceivable, but only for the TiO2 matrix. Furthermore, the application of a plasma treatment allowed to better expose the nanoparticles, providing a further enhancement of Raman signals.

Anti-Cancer Drug Sensitivity Assay with Quantitative Heterogeneity Testing Using Single-Cell Raman Spectroscopy.

A novel anti-cancer drug sensitivity testing (DST) approach was developed based on in vitro single-cell Raman spectrum intensity (RSI). Generally, the intensity of Raman spectra (RS) for a single living cell treated with drugs positively relates to the sensitivity of the cells to the drugs. In this study, five cancer cell lines (BGC 823, SGC 7901, MGC 803, AGS, and NCI-N87) were exposed to three cytotoxic compounds or to combinations of these compounds, and then they were evaluated for their responses with RSI. The results of RSI were consistent with conventional DST methods. The parametric correlation coefficient for the RSI and Methylthiazolyl tetrazolium assay (MTT) was 0.8558 ± 0.0850, and the coefficient of determination was calculated as R2 = 0.9529 ± 0.0355 for fitting the dose–response curve. Moreover, RSI data for NCI-N87 cells treated by trastuzumab, everolimus (cytostatic), and these drugs in combination demonstrated that the RSI method was suitable for testing the sensitivity of cytostatic drugs. Furthermore, a heterogeneity coefficient H was introduced for quantitative characterization of the heterogeneity of cancer cells treated by drugs. The largest possible variance between RSs of cancer cells were quantitatively obtained using eigenvalues of principal component analysis (PCA). The ratio of H between resistant cells and sensitive cells was greater than 1.5, which suggested the H-value was effective to describe the heterogeneity of cancer cells. Briefly, the RSI method might be a powerful tool for simple and rapid detection of the sensitivity of tumor cells to anti-cancer drugs and the heterogeneity of their responses to these drugs.

Micro-EDM method to fabricate three-dimensional surface textures used as SERS-active substrate

Based on micro electrical discharge machining (micro-EDM) method, three-dimensional surface textures were fabricated by constituting arrayed paraboloid-shaped micro-cavities on a copper template, and these surface textures were intended for surface-enhanced Raman scattering (SERS) active substrate. By lowering discharge energy, the inherent discharge craters and bulges were limited to be in nanoscale, and thereby the fabricated surface texture could be characterized as a micro-nano hierarchical structure. Raman spectra were measured on fabricated surface textures using Rhodamine 6G as the probe molecule, and results showed that the characteristic peaks of R6G molecules can be successfully identified under a low concentration of 10−7 M. In addition, the strongest Raman spectra intensity was observed on the surface texture that has the largest apparent area (S) per unit interval space (d) and per unit peak-to-valley height (h). This is mainly attributed to the fact that the surface texture with larger S/(d × h) would adsorb more probe molecules and provide higher density of SERS hot-spots. As a whole, the fabricated surface textures exhibited good SERS performances by providing an enhancement factor of greater than 107. The works conducted in this study are expected to provide a novel thought to fabricate SERS-active substrate, and extend the application fields of micro-EDM technology as well.

Mathematical modeling of paddy (Oryza sativa) hydration in different thermal conditions assisted by Raman spectroscopy

Hydration is the main step of rice parboiling process because it promotes starch gelatinization. The present study presents empirical and phenomenological models for rice hydration at different thermal conditions, as well as evaluations of changes in functional groups of the rice grain during the process. The empirical models of Weibull, Henderson and Pabis, the phenomenological models of Omoto and a diffusive model based on Fick's second law were considered. Additionally Raman Spectroscopy of the grain during hydration is performed. Among the models, Fick's model presents better adherence to the experimental results. It was observed that its effective diffusion coefficient varies with temperature according to Arrhenius equation, providing an estimate of the activation energy of the hydration process. It was also observed that Raman spectra intensity decreases during the hydration process as moisture increases. This suggests that Raman spectroscopy may be employed for monitoring the industrial rice parboiling process.

Laser crater enhanced Raman spectroscopy.

Raman signal enhancement by multiple scattering inside laser crater cones was observed for the first time, to the best of our knowledge. Laser crater enhanced Raman spectroscopy (LCERS) yielded a 14-fold increase in the Raman spectra bands due to efficient multiple scattering of laser irradiation within the laser crater walls. The same pulsed Nd:YAG laser (532nm, 10ns) was used for both laser crater formation and Raman scattering experiments by varying the output pulse energy. First, powerful pulses are used to produce the laser crater; then low-energy pulses are used to perform Raman scattering measurements. The laser crater profile and its alignment with the laser beam waist were found to be the key parameters for the optimization of the Raman spectrum intensity enhancement. Raman intensity enhancement resulted from increased surface scattering area at the crater walls, rather than spatially offset Raman scattering. The increased signal-to-noise ratio resulted in limits of detection improvement for quantitative analysis using LCERS.

Ag nanoparticles cladded with parylene for high-stability microfluidic surface-enhanced Raman scattering (SERS) biochemical sensing

A method for fabricating the stable and reusable microfluidic-integrated devices based on the Ag nanoparticles cladded with parylene have been demonstrated, which can be applied for biochemical sensing. The excellent parylene cladding structure acted as a protection layer for the Ag nanoparticles, enhancing the Raman spectrum intensity by forming the hot spot structure between the nanoparticles. By optimizing the parylene film thickness, the surface enhanced Raman spectroscopy sensitivity of the R6G solution could be enhanced by three times, comparing with the initial substrate. The hydrophobic and biocompatible parylene cladding film also increased the repulsive to the molecular probes, enabling hundreds of measurement cycles and greatly increasing the stability and reproducibility. This method was also demonstrated to be reusable by flushing with water and alcohol through the integrated micro-channel.

Basis set dependence using DFT/B3LYP calculations to model the Raman spectrum of thymine

Raman spectroscopy (including surface enhanced Raman spectroscopy (SERS) and tip enhanced Raman spectroscopy (TERS)) is a highly promising experimental method for investigations of biomolecule damage induced by ionizing radiation. However, proper interpretation of changes in experimental spectra for complex systems is often difficult or impossible, thus Raman spectra calculations based on density functional theory (DFT) provide an invaluable tool as an additional layer of understanding of underlying processes. There are many works that address the problem of basis set dependence for energy and bond length consideration, nevertheless there is still lack of consistent research on basis set influence on Raman spectra intensities for biomolecules. This study fills this gap by investigating of the influence of basis set choice for the interpretation of Raman spectra of the thymine molecule calculated using the DFT/B3LYP framework and comparing these results with experimental spectra. Among 19 selected Pople's basis sets, the best agreement was achieved using 6-31[Formula: see text](d,p), 6-31[Formula: see text](d,p) and 6-11[Formula: see text]G(d,p) sets. Adding diffuse functions or polarized functions for small basis set or use of a medium or large basis set without diffuse or polarized functions is not sufficient to reproduce Raman intensities correctly. The introduction of the diffuse functions ([Formula: see text]) on hydrogen atoms is not necessary for gas phase calculations. This work serves as a benchmark for further research on the interaction of ionizing radiation with DNA molecules by means of ab initio calculations and Raman spectroscopy. Moreover, this work provides a set of new scaling factors for Raman spectra calculation in the framework of DFT/B3LYP method.