Detection of carbon nanotubes in bovine raw milk through Fourier transform Raman spectroscopy.

The potential use of carbon-based methodologies for drug delivery and reproductive biology in cows raises concerns about residues in milk and food safety. This study aimed to assess the potential of Fourier transform Raman spectroscopy and discriminant analysis using partial least squares (PLS-DA) to detect functionalized multiwalled carbon nanotubes (MWCNT) in bovine raw milk. Oxidized MWCNT were diluted in milk at different concentrations from 25.00 to 0.01 µg/mL. Raman spectroscopy measurements and PLS-DA were performed to identify low concentrations of MWCNT in milk samples. The PLS-DA model was characterized by the analysis of the variable importance in projection (VIP) scores. All the training samples were correctly classified by the model, resulting in no false-positive or false-negative classifications. For test samples, only one false-negative result was observed, for 0.01 µg/mL MWCNT dilution. The association between Raman spectroscopy and PLS-DA was able to identify MWCNT diluted in milk samples up to 0.1 µg/mL. The PLS-DA model was built and validated using a set of test samples and spectrally interpreted based on the highest VIP scores. This allowed the identification of the vibrational modes associated with the D and G bands of MWCNT, as well as the milk bands, which were the most important variables in this analysis.

Gold nanoparticles for surface-enhanced Raman scattering detection of benzyldimethyldodecylammonium chloride at low concentration.

The oil and gas industry plays a vital role in the global economy. The production process has several critical conditions and can expose metals to corrosion. Surfactants like the quaternary ammonium salt Benzyldimethyldodecylammonium Bromide (BDAC) are currently used to prevent corrosions; classical methods for determining these surfactants have problems in saline samples and usually present high costs. In this context, spectroscopic techniques become an excellent alternative for quaternary ammonium salts detection. Here, a SERS (surface-enhanced Raman scattering) sensor based on gold nanoparticles (AuNPs) synthesized through chemical reduction was used as an alternative method for BDAC detection. We detected BDAC at low concentrations in water solutions: at 5 to 30 ppm (1.47 × 10-5 mol L-1 to 8.82 × 10-5 mol L-1); and had the vibration attempt attribute analyzed. A new study of quaternary ammonium compounds using AuNPs and SERS with a different, easy, and repeatable approach to spectra acquisition is presented and shows to be a promising method applied in quaternary ammonium salt compounds detection for the oil and gas industry.

Combining surface-enhanced Raman spectroscopy and paper spray mass spectrometry for the identification and confirmation of psychotropic substances in alcoholic beverages.

Criminal practices in which an individual becomes vulnerable and prone to sexual assault after ingesting drinks spiked with doping substances have become a social concern globally. As forensic protocols require a multi-tiered strategy for chemical evidentiary analysis, the backlog of evidence has become a significant problem in the community. Herein, a fast, sensible, and complementary dual analytical methodology was developed using a single commercial paper substrate for surface-enhanced Raman spectroscopy (SERS) and paper spray mass spectrometry (PS-MS) analysis to identify psychotropic substances added to alcoholic beverages irrefutably. To study and investigate this criminal practice, pharmaceutical formulations containing distinct psychotropic substances (zolpidem, clonazepam, diazepam, and ketamine) were added to drinks typically consumed at parties and festivals (Pilsen beer, açaí Catuaba®, gin tonic, and vodka mixed with Coca-Cola Zero®). A simple liquid-liquid extraction with a low-temperature partitioning (LLE-LTP) procedure was applied to the drinks and effectively minimized matrix effects. As a preliminary analysis, SERS spectra combined with Hierarchical Clustering Analysis (HCA) provided sufficient information to investigate the samples further. The presence of the protonated species for the psychotropic substances in the spiked drinks was readily verified in the mass spectra and confirmed by tandem mass spectrometry. Finally, the results demonstrate the potential of this methodology to be easily implemented into the routine of forensic laboratories and to be further employed at harm reduction tends at parties and festivals to detect contaminated beverages promptly and irrefutably as an efficient tool to prevent such crimes.

Selective Electron-Phonon Coupling in Dimerized 1T-TaS2 Revealed by Resonance Raman Spectroscopy.

The layered transition-metal dichalcogenide material 1T-TaS2 possesses successive phase transitions upon cooling, resulting in strong electron-electron correlation effects and the formation of charge density waves (CDWs). Recently, a dimerized double-layer stacking configuration was shown to form a Peierls-like instability in the electronic structure. To date, no direct evidence for this double-layer stacking configuration using optical techniques has been reported, in particular through Raman spectroscopy. Here, we employ a multiple excitation and polarized Raman spectroscopy to resolve the behavior of phonons and electron-phonon interactions in the commensurate CDW lattice phase of dimerized 1T-TaS2. We observe a distinct behavior from what is predicted for a single layer and probe a richer number of phonon modes that are compatible with the formation of double-layer units (layer dimerization). The multiple-excitation results show a selective coupling of each Raman-active phonon with specific electronic transitions hidden in the optical spectra of 1T-TaS2, suggesting that selectivity in the electron-phonon coupling must also play a role in the CDW order of 1T-TaS2.

Degree of conversion and microhardness of resin cements photoactivated through glass ceramic.

BACKGROUND: To assess whether glass-ceramic shade, thickness and translucency affect degree of conversion (DC) and Knoop microhardness (KHN) of resin cements photoactivated using light-emitting diode (LED) or quartz-tungsten-halogen (QTH) units. MATERIAL AND METHODS: Glass-ceramic blocks were cut (2, 3 and 4mm) and sintered. For DC FT Raman spectroscopy (n=3), film specimens of cements (RelyX ARC, U200, Veneer, C&B) were obtained. For KHN test (n=3), cements were inserted in cylindrical matrix and covered by polyester strip. Specimens were photoactivated (30s) using LED or QTH according to each group: direct photoactivation (DP), interposing ceramic specimens or no photoactivation (NP). Data were analysed by ANOVA and Tukey's test, Kruskal-Wallis and Dunn's tests (p<0.05). RESULTS: Ceramic features had significant effect on DC of RelyX ARC, U200 and Veneer (p<0.0017). Light source had no effect (p=0.9512). C&B and Veneer had higher DC, followed by dual cements. NP dual cements showed the lowest DC. For KHN, ceramic shade (p=0.1717) and light source (p=0.1421) were not significant, but ceramic translucency, thickness and resin cement were significant (p=0.0001). KHN was higher for U200 followed by ARC, and lowest for Veneer. CONCLUSIONS: DC was affected by ceramic shade, translucency and thickness. KHN was dependent on ceramic translucency and thickness. Higher DC and KHN were achieved for dual-cured cements photoactivated through 2mm-thick low translucent or 3mm-thick high translucent glass-ceramic. Key words:Cementation, composite resin cements, dental curing lights, glass ceramics.

Origin of the Giant Enhanced Raman Scattering by Sulfur Chains Encapsulated inside Single-Wall Carbon Nanotubes.

In this work, we explain the origin and the mechanism responsible for the strong enhancement of the Raman signal of sulfur chains encapsulated by single-wall carbon nanotubes by running resonance Raman measurements in a wide range of excitation energies for two nanotube samples with different diameter distributions. The Raman signal associated with the vibrational modes of the sulfur chain is observed when it is confined by small-diameter metallic nanotubes. Moreover, a strong enhancement of the Raman signal is observed for excitation energies corresponding to the formation of excited nanotube-chain-hybrid electronic states. Our hypothesis was further tested by high pressure Raman measurements and confirmed by density functional theory calculations of the electronic density of states of hybrid systems formed by sulfur chains encapsulated by different types of single-wall carbon nanotubes.

Discrimination between conventional and omega-3 fatty acids enriched eggs by FT-Raman spectroscopy and chemometric tools.

This work developed an analytical method to differentiate conventional and omega-3 fat acids enriched eggs by Raman spectroscopy and multivariate supervised classification with Partial Least Squares Discriminant Analysis (PLS-DA). Forty samples of enriched eggs and forty samples of different types of common eggs from different batches were used to build the model. Firstly, gas chromatography was employed to analyze fatty acid profiles in egg samples. Raman spectra of the yolk extracts were recorded in the range from 3100 to 990 cm-1. PLS-DA model was able to correctly classify samples with nearly 100% success rate. This model was validated estimating appropriate figures of merit. Predictions uncertainties were also estimated by bootstrap resampling. The most discriminant Raman modes were identified based on VIP (variables importance in projection) scores. This method has potential to assist food industries and regulatory agencies for food quality control, allowing detecting frauds and enabling faster and reliable analyzes.

Toxicological assessment of PEGylated single-walled carbon nanotubes in early developing zebrafish.

Functionalization of single-walled carbon nanotubes (SWCNT) with polyethylene glycol (PEG) is among the most promising strategies to avoid SWCNT aggregation in aqueous media, improving its interactions with biological systems. However, the best molecular PEG weight and functionalization strategy remain under investigation. In this work we assessed the toxicological effects of SWCNT functionalized with PEG at 600 Da in zebrafish embryos. Embryos were exposed to SWCNT at 0.01, 0.1 and 1 mg/L from 3 to 96 h post-fertilization (hpf). At the highest concentration, SWCNT led to toxic effects at several endpoints, including mortality, delayed hatching, malformations, reduced body length, increased ROS production and DNA damage. Even with these effects, SWCNT could not be detected within the bodily tissues of the larvae. Our results give evidence that the tested PEGylation approach was unsuitable to avoid SWCNT aggregation in aqueous media, and that SWCNT can induce toxicity even without being absorbed by the organism by obstructing the chorion pores.

Intervalley scattering by acoustic phonons in two-dimensional MoS2 revealed by double-resonance Raman spectroscopy.

Double-resonance Raman scattering is a sensitive probe to study the electron-phonon scattering pathways in crystals. For semiconducting two-dimensional transition-metal dichalcogenides, the double-resonance Raman process involves different valleys and phonons in the Brillouin zone, and it has not yet been fully understood. Here we present a multiple energy excitation Raman study in conjunction with density functional theory calculations that unveil the double-resonance Raman scattering process in monolayer and bulk MoS2. Results show that the frequency of some Raman features shifts when changing the excitation energy, and first-principle simulations confirm that such bands arise from distinct acoustic phonons, connecting different valley states. The double-resonance Raman process is affected by the indirect-to-direct bandgap transition, and a comparison of results in monolayer and bulk allows the assignment of each Raman feature near the M or K points of the Brillouin zone. Our work highlights the underlying physics of intervalley scattering of electrons by acoustic phonons, which is essential for valley depolarization in MoS2.

Toxicity of single-wall carbon nanotubes functionalized with polyethylene glycol in zebrafish (Danio rerio) embryos.

Single-wall carbon nanotubes functionalized with polyethylene glycol (SWCNT-PEG) are promising materials for biomedical applications such as diagnostic devices and controlled drug-release systems. However, several questions about their toxicological profile remain unanswered. Thus, the aim of this study was to investigate the action of SWCNT-PEG in Danio rerio zebrafish embryos at the molecular, physiological and morphological levels. The SWCNT used in this study were synthesized by the high-pressure carbon monoxide process, purified and then functionalized with distearoyl phosphatidylethanolamine block copolymer-PEG (molecular weight 2 kDa). The characterization process was carried out with low-resolution transmission electron microscopy, thermogravimetric analysis and Raman spectroscopy. Individual zebrafish embryos were exposed to the SWCNT-PEG. Toxic effects occurred only at the highest concentration tested (1 ppm) and included high mortality rates, delayed hatching and decreased total larval length. For all the concentrations tested, the alkaline comet assay revealed no genotoxicity, and Raman spectroscopy measurements on the histological slices revealed no intracellular nanotubes. The results shown here demonstrate that SWCNT-PEG has low toxicity in zebrafish embryos, but more studies are needed to understand what mechanisms are involved. However, the presence of residual metals is possibly among the primary mechanisms responsible for the toxic effects observed, because the purification process was not able to remove all metal contamination, as demonstrated by the thermogravimetric analysis. More attention must be given to the toxicity of these nanomaterials before they are used in biomedical applications. Copyright © 2016 John Wiley & Sons, Ltd.

Unravelling the mechanisms of reactive oxygen species formation in nanohybrid systems of porphyrins and enriched (6,5) single-walled carbon nanotubes for photosensitization.

Nanohybrids of enriched (6,5) single-walled semiconducting carbon nanotubes (E-SWCNTs) and porphyrin can be used synergistically as photodynamic therapy (PDT) agents. The efficiency of different porphyrins within the nanohybrids was investigated and compared with results obtained from porphyrins in previous studies. Reactive oxygen species singlet oxygen (1)O2 and for the first time hydroxyl radical ˙OH generation by the nanohybrids under illumination were detected by electron paramagnetic resonance using spin trapping molecules TEMP and PBN. Based on the analysis, we improve the modelling of charge transport within the nanohybrids, which is also detected by Raman scattering. It is shown that the 5,10,15,20-tetrakis(4-trimethylammoniumphenyl)porphyrin [H2TTMAPP(OTs)4] and E-SWCNT form very efficient nanohybrids for PDT applications in the visible spectral range.

Erratum: Symmetry-Dependent Exciton-Phonon Coupling in 2D and Bulk MoS_{2} Observed by Resonance Raman Scattering [Phys. Rev. Lett. 114, 136403 (2015)].

This corrects the article DOI: 10.1103/PhysRevLett.114.136403.

Biopersistence of PEGylated Carbon Nanotubes Promotes a Delayed Antioxidant Response after Infusion into the Rat Hippocampus.

Carbon nanotubes are promising nanomaterials for the diagnosis and treatment of brain disorders. However, the ability of these nanomaterials to cross cell membranes and interact with neural cells brings the need for the assessment of their potential adverse effects on the nervous system. This study aimed to investigate the biopersistence of single-walled carbon nanotubes functionalized with polyethylene glycol (SWCNT-PEG) directly infused into the rat hippocampus. Contextual fear conditioning, Y-maze and open field tasks were performed to evaluate the effects of SWCNT-PEG on memory and locomotor activity. The effects of SWCNT-PEG on oxidative stress and morphology of the hippocampus were assessed 1 and 7 days after infusion of the dispersions at 0.5, 1.0 and 2.1 mg/mL. Raman analysis of the hippocampal homogenates indicates the biopersistence of SWCNT-PEG in the hippocampus 7 days post-injection. The infusion of the dispersions had no effect on the acquisition or persistence of the contextual fear memory; likewise, the spatial recognition memory and locomotor activity were not affected by SWCNT-PEG. Histological examination revealed no remarkable morphological alterations after nanomaterial exposure. One day after the infusion, SWCNT-PEG dispersions at 0.5 and 1.0 mg/mL were able to decrease total antioxidant capacity without modifying the levels of reactive oxygen species or lipid hydroperoxides in the hippocampus. Moreover, SWCNT-PEG dispersions at all concentrations induced antioxidant defenses and reduced reactive oxygen species production in the hippocampus at 7 days post-injection. In this work, we found a time-dependent change in antioxidant defenses after the exposure to SWCNT-PEG. We hypothesized that the persistence of the nanomaterial in the tissue can induce an antioxidant response that might have provided resistance to an initial insult. Such antioxidant delayed response may constitute an adaptive response to the biopersistence of SWCNT-PEG in the hippocampus.

Symmetry-dependent exciton-phonon coupling in 2D and bulk MoS2 observed by resonance Raman scattering.

This work describes a resonance Raman study performed on samples with one, two, and three layers (1L, 2L, 3L), and bulk MoS2, using more than 30 different laser excitation lines covering the visible range, and focusing on the intensity of the two most pronounced features of the Raman scattering spectrum of MoS2 (E2g(1) and A1g bands). The Raman excitation profiles of these bands were obtained experimentally, and it is found that the A1g feature is enhanced when the excitation laser is in resonance with A and B excitons of MoS2, while the E2g1 feature is shown to be enhanced when the excitation laser is close to 2.7 eV. We show from the symmetry analysis of the exciton-phonon interaction that the mode responsible for the E2g(1) resonance is identified as the high energy C exciton recently predicted [D. Y. Qiu, F. H. da Jornada, and S. G. Louie, Phys. Rev. Lett. 111, 216805 (2013)].

Comparative study of Raman spectroscopy in graphene and MoS2-type transition metal dichalcogenides.

CONSPECTUS: Raman spectroscopy is one of the most powerful experimental tools to study graphene, since it provides much useful information for sample characterization. In this Account, we show that this technique is also convenient to study other bidimensional materials beyond graphene, and we will focus on the semiconducting transition metal dichalcogenides (MX2), specifically on MoS2 and WS2. We start by comparing the atomic structure of graphene and 2H-MX2 as a function of the number of layers in the sample. The first-order Raman active modes of each material can be predicted on the basis of their corresponding point-group symmetries. We show the analogies between graphene and 2H-MX2 in their Raman spectra. Using several excitation wavelengths in the visible range, we analyze the first- and second-order features presented by each material. These are the E2g and 2TO(K) bands in graphene (also known as the G and 2D bands, respectively) and the A1', E', and 2LA(M) bands in 2H MX2. The double-resonance processes that originate the second-order bands are different for both systems, and we will discuss them in terms of the different electronic structure and phonon dispersion curves presented by each compound. According to the electronic structure of graphene, which is a zero band gap semiconductor, the Raman spectrum is resonant for all the excitation wavelengths. Moreover, due to the linear behavior of the electronic dispersion near the K point, the double-resonance bands of graphene are dispersive, since their frequencies vary when we change the laser energy used for the sample excitation. In contrast, the semiconducting MX2 materials present an excitonic resonance at the direct gap, and consequently, the double-resonance Raman bands of MX2 are not dispersive, and only their intensities depend on the laser energy. In this sense, resonant Raman scattering experiments performed in transition metal dichalcogenides using a wide range of excitation energies can provide information about the electronic structure of these materials, which is complementary to other optical spectroscopies, such as absorption or photoluminescence. Raman spectroscopy can also be useful to address disorder in MX2 samples in a similar way as it is used in graphene. Both materials exhibit additional Raman features associated with phonons within the interior of the Brillouin zone that are activated by the presence of defects and that are not observed in pristine samples. Such is the case of the well-known D band of graphene. MX2 samples present analogous features that are clearly observed at specific excitation energies. The origins of these double-resonance Raman bands in MX2 are still subjects of current research. Finally, we discuss the suitability of Raman spectroscopy as a strain or doping sensor. Such applications of Raman spectroscopy are being extensively studied in the case of graphene, and considering its structural analogies with MX2 systems, we show how this technique can also be used to provide strain/doping information for transition metal dichalcogenides.

Excited excitonic states in 1L, 2L, 3L, and bulk WSe2 observed by resonant Raman spectroscopy.

Resonant Raman spectroscopy (RRS) is a very useful tool to study physical properties of materials since it provides information about excitons and their coupling with phonons. We present in this work a RRS study of samples of WSe2 with one, two, and three layers (1L, 2L, and 3L), as well as bulk 2H-WSe2, using up to 20 different laser lines covering the visible range. The first- and second-order Raman features exhibit different resonant behavior, in agreement with the double (and triple) resonance mechanism(s). From the laser energy dependence of the Raman intensities (Raman excitation profile, or REP), we obtained the energies of the excited excitonic states and their dependence with the number of atomic layers. Our results show that Raman enhancement is much stronger for the excited A' and B' states, and this result is ascribed to the different exciton-phonon coupling with fundamental and excited excitonic states.

Biodistribution and toxicological study of PEGylated single-wall carbon nanotubes in the zebrafish (Danio rerio) nervous system.

Nanotechnology has been proven to be increasingly compatible with pharmacological and biomedical applications. Therefore, we evaluated the biological interactions of single-wall carbon nanotubes functionalized with polyethylene glycol (SWNT-PEG). For this purpose, we analyzed biochemical, histological, behavioral and biodistribution parameters to understand how this material behaves in vitro and in vivo using the fish Danio rerio (zebrafish) as a biological model. The in vitro results for fish brain homogenates indicated that SWNT-PEG had an effect on lipid peroxidation and GSH (reduced glutathione) content. However, after intraperitoneal exposure, SWNT-PEG proved to be less biocompatible and formed aggregates, suggesting that the PEG used for the nanoparticle functionalization was of an inappropriate size for maintaining product stability in a biological environment. This problem with functionalization may have contributed to the low or practically absent biodistribution of SWNT-PEG in zebrafish tissues, as verified by Raman spectroscopy. There was an accumulation of material in the abdominal cavity that led to inflammation and behavioral disturbances, as evaluated by a histological analysis and an open field test, respectively. These results provide evidence of a lack of biocompatibility of SWNTs modified with short chain PEGs, which leads to the accumulation of the material, tissue damage and behavioral alterations in the tested subjects.