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1.
Phys Chem Chem Phys ; 24(2): 1183-1190, 2022 Jan 04.
Artículo en Inglés | MEDLINE | ID: mdl-34931633

RESUMEN

This work reports a classification analysis method based on the vibrational Raman spectra of 38 quinones and related structures, spectrally ordering and classifying the compounds. The molecular systems are relevant for chemical and biological processes, with applications in pharmacology, toxicology and medicine. The classification strategy uses a combination of principal component analysis with K-means clustering methods. Both theoretical simulations and experimental data are analysed, thus establishing their spectral characteristics, as related to their chemical structures and properties. The protocol introduced here should be broadly applicable in other molecular and solid state systems.

2.
Phys Chem Chem Phys ; 23(41): 23428-23444, 2021 Oct 27.
Artículo en Inglés | MEDLINE | ID: mdl-34651627

RESUMEN

Raman spectroscopy has been established as a valuable tool to study and characterize two-dimensional (2D) systems, but it exhibits two drawbacks: a relatively weak signal response and a limited spatial resolution. Recently, advanced Raman spectroscopy techniques, such as coherent anti-Stokes spectroscopy (CARS), stimulated Raman scattering (SRS) and tip-enhanced Raman spectroscopy (TERS), have been shown to overcome these two limitations. In this article, we review how useful physical information can be retrieved from different 2D materials using these three advanced Raman spectroscopy and imaging techniques, discussing results on graphene, hexagonal boron-nitride, and transition metal di- and mono-chalcogenides, thus providing perspectives for future work in this early-stage field of research, including similar studies on unexplored 2D systems and open questions.

3.
Analyst ; 146(19): 6014-6025, 2021 Sep 27.
Artículo en Inglés | MEDLINE | ID: mdl-34505596

RESUMEN

The deposition of amyloid plaques is considered one of the main microscopic features of Alzheimer's disease (AD). Since plaque formation can precede extensive neurodegeneration and it is the main clinical manifestation of AD, it constitutes a relevant target for new treatment and diagnostic approaches. Micro-Raman spectroscopy, a label-free technique, is an accurate method for amyloid plaque identification and characterization. Here, we present a high spatial resolution micro-Raman hyperspectral study in transgenic APPswePS1ΔE9 mouse brains, showing details of AD tissue biochemical and histological changes without staining. First we used stimulated micro-Raman scattering to identify the lipid-rich halo surrounding the amyloid plaque, and then proceeded with spontaneous (conventional) micro-Raman spectral mapping, which shows a cholesterol and sphingomyelin lipid-rich halo structure around dense-core amyloid plaques. The detailed images of this lipid halo relate morphologically well with dystrophic neurites surrounding plaques. Principal Component Analysis (PCA) of the micro-Raman hyperspectral data indicates the feasibility of the optical biomarkers of AD progression with the potential for discriminating transgenic groups of young adult mice (6-month-old) from older ones (12-month-old). Frequency-specific PCA suggests that plaque-related neurodegeneration is the predominant change captured by Raman spectroscopy, and the main differences are highlighted by vibrational modes associated with cholesterol located majorly in the lipid halo.


Asunto(s)
Enfermedad de Alzheimer , Placa Amiloide , Envejecimiento , Enfermedad de Alzheimer/diagnóstico , Péptidos beta-Amiloides , Animales , Encéfalo , Lípidos , Ratones , Ratones Transgénicos , Espectrometría Raman
4.
J Phys Chem Lett ; 12(31): 7625-7631, 2021 Aug 12.
Artículo en Inglés | MEDLINE | ID: mdl-34351150

RESUMEN

Understanding the impact of doping variations on the physical properties of two-dimensional materials is important for their application in electronic and optoelectronic devices. Here we report a nano-optical study on graphene and MoS2 homojunctions by placing these two materials partly on top of a layered talc substrate, partly on top of an SiO2 substrate. By analyzing the nano-Raman scattering from graphene and the nanophotoluminescense emission from MoS2, two different doping zones are evident with sub-100 nm wide charge oscillations. The oscillations occur abruptly at the homojuction and extend over longer distances away from the interface, indicating imperfect deposition of the two-dimensional layer on the substrate. These results evidence fine and unexpected details of the homojuctions, important to build better electronic and optoelectronic devices.

5.
Analyst ; 146(9): 2945-2954, 2021 May 04.
Artículo en Inglés | MEDLINE | ID: mdl-33949418

RESUMEN

Given the long subclinical stage of Alzheimer's disease (AD), the study of biomarkers is relevant both for early diagnosis and the fundamental understanding of the pathophysiology of AD. Biomarkers provided by Amyloid-ß (Aß) plaques have led to an increasing interest in characterizing this hallmark of AD due to its promising potential. In this work, we characterize Aß plaques by label-free multimodal imaging: we combine two-photon excitation autofluorescence (TPEA), second harmonic generation (SHG), spontaneous Raman scattering (SpRS), coherent anti-Stokes Raman scattering (CARS), and stimulated Raman scattering (SRS) to describe and compare high-resolution images of Aß plaques in brain tissues of an AD mouse model. Comparing single-laser techniques images, we discuss the origin of the SHG, which can be used to locate the plaque core reliably. We study both the core and the halo with vibrational microscopy and compare SpRS and SRS microscopies for different frequencies. We also combine SpRS spectroscopy with SRS microscopy and present two core biomarkers unexplored with SRS microscopy: phenylalanine and amide B. We provide high-resolution SRS images with the spatial distribution of these biomarkers in the plaque and compared them with images of the amide I distribution. The obtained spatial correlation corroborates the feasibility of these biomarkers in the study of Aß plaques. Furthermore, since amide B enables rapid imaging, we discuss its potential as a novel fingerprint for diagnostic applications.


Asunto(s)
Enfermedad de Alzheimer , Enfermedad de Alzheimer/diagnóstico por imagen , Péptidos beta-Amiloides , Animales , Ratones , Microscopía , Placa Amiloide/diagnóstico por imagen , Espectrometría Raman
6.
Nat Commun ; 12(1): 2980, 2021 05 20.
Artículo en Inglés | MEDLINE | ID: mdl-34016995

RESUMEN

Near field scanning Microwave Impedance Microscopy can resolve structures as small as 1 nm using radiation with wavelengths of 0.1 m. Combining liquid immersion microscopy concepts with exquisite force control exerted on nanoscale water menisci, concentration of electromagnetic fields in nanometer-size regions was achieved. As a test material we use twisted bilayer graphene, because it provides a sample where the modulation of the moiré superstructure pattern can be systematically tuned from Ångstroms up to tens of nanometers. Here we demonstrate that a probe-to-pattern resolution of 108 can be obtained by analyzing and adjusting the tip-sample distance influence on the dynamics of water meniscus formation and stability.

7.
Nature ; 590(7846): 405-409, 2021 02.
Artículo en Inglés | MEDLINE | ID: mdl-33597759

RESUMEN

Twisted bilayer graphene is created by slightly rotating the two crystal networks in bilayer graphene with respect to each other. For small twist angles, the material undergoes a self-organized lattice reconstruction, leading to the formation of a periodically repeated domain1-3. The resulting superlattice modulates the vibrational3,4 and electronic5,6 structures within the material, leading to changes in the behaviour of electron-phonon coupling7,8 and to the observation of strong correlations and superconductivity9. However, accessing these modulations and understanding the related effects are challenging, because the modulations are too small for experimental techniques to accurately resolve the relevant energy levels and too large for theoretical models to properly describe the localized effects. Here we report hyperspectral optical images, generated by a nano-Raman spectroscope10, of the crystal superlattice in reconstructed (low-angle) twisted bilayer graphene. Observations of the crystallographic structure with visible light are made possible by the nano-Raman technique, which reveals the localization of lattice dynamics, with the presence of strain solitons and topological points1 causing detectable spectral variations. The results are rationalized by an atomistic model that enables evaluation of the local density of the electronic and vibrational states of the superlattice. This evaluation highlights the relevance of solitons and topological points for the vibrational and electronic properties of the structures, particularly for small twist angles. Our results are an important step towards understanding phonon-related effects at atomic and nanometric scales, such as Jahn-Teller effects11 and electronic Cooper pairing12-14, and may help to improve device characterization15 in the context of the rapidly developing field of twistronics16.

8.
J Environ Manage ; 279: 111685, 2021 Feb 01.
Artículo en Inglés | MEDLINE | ID: mdl-33321351

RESUMEN

In this work, chemical and structural properties of various biochars were analyzed and compared with those from a highly stable anthropic soil, Terra Preta de Índio (TPI). TPI is believed to be responsible for the fertility of Amazonian soils and their stability; therefore, the production of a synthetic TPI would be of great interest for agricultural applications. Biochar produced from different raw biomasses were comprehensively characterized and, based on the obtained results, a preliminary study was performed testing three different routes of chemical activation using nitric acid, phosphoric acid, and potassium hydroxide as activating agents. After chemical activations, metal contents in the biochars decreased, as expected, and high degrees of carbonization were observed. In the case of the activation performed with HNO3, intense signals related to carboxylic groups in TG-MS analysis and in potentiometric titrations point out to a highly oxygenated biochar. Structural analysis showed that activations generated point defects in sp2-carbon structures of biochar, with the material obtained after KOH activation showing a high surface area (569 m2 g-1), an important feature for the use as soil amendment.


Asunto(s)
Carbón Orgánico , Suelo , Agricultura , Biomasa
9.
Beilstein J Nanotechnol ; 11: 1801-1808, 2020.
Artículo en Inglés | MEDLINE | ID: mdl-33335824

RESUMEN

Folds naturally appear on nanometrically thin materials, also called "2D materials", after exfoliation, eventually creating folded edges across the resulting flakes. We investigate the adhesion and flexural properties of single-layered and multilayered 2D materials upon folding in the present work. This is accomplished by measuring and modeling mechanical properties of folded edges, which allows for the experimental determination of the bending stiffness (κ) of multilayered 2D materials as a function of the number of layers (n). In the case of talc, we obtain κ ∝ n 3 for n ≥ 5, indicating no interlayer sliding upon folding, at least in this thickness range. In contrast, tip-enhanced Raman spectroscopy measurements on edges in folded graphene flakes, 14 layers thick, show no significant strain. This indicates that layers in graphene flakes, up to 5 nm thick, can still slip to relieve stress, showing the richness of the effect in 2D systems. The obtained interlayer adhesion energy for graphene (0.25 N/m) and talc (0.62 N/m) is in good agreement with recent experimental results and theoretical predictions. The obtained value for the adhesion energy of graphene on a silicon substrate is also in agreement with previous results.

10.
Nanotechnology ; 31(49): 495702, 2020 Dec 04.
Artículo en Inglés | MEDLINE | ID: mdl-32990274

RESUMEN

Phonons play a fundamental role in the electronic and thermal transport of 2D materials which is crucial for device applications. In this work, we investigate the temperature-dependence of A[Formula: see text] and A[Formula: see text] Raman modes of suspended and supported mechanically exfoliated few-layer gallium sulfide (GaS), accessing their relevant thermodynamic Grüneisen parameters and anharmonicity. The Raman frequencies of these two phonons soften with increasing temperature with different [Formula: see text] temperature coefficients. The first-order temperature coefficients θ of A[Formula: see text] mode is ∼ -0.016 cm-1/K, independent of the number of layers and the support. In contrast, the θ of A[Formula: see text] mode is smaller for two-layer GaS and constant for thicker samples (∼ -0.006 2 cm-1 K-1). Furthermore, for two-layer GaS, the θ value is ∼ -0.004 4 cm-1 K-1 for the supported sample, while it is even smaller for the suspended one (∼ -0.002 9 cm-1 K-1). The higher θ value for supported and thicker samples was attributed to the increase in phonon anharmonicity induced by the substrate surface roughness and Umklapp phonon scattering. Our results shed new light on the influence of the substrate and number of layers on the thermal properties of few-layer GaS, which are fundamental for developing atomically-thin GaS electronic devices.

11.
J Chem Phys ; 153(11): 114201, 2020 Sep 21.
Artículo en Inglés | MEDLINE | ID: mdl-32962365

RESUMEN

Plasmon-tunable tip pyramids (PTTPs) are reproducible and efficient nanoantennas for tip-enhanced Raman spectroscopy (TERS). Their fabrication method is based on template stripping of a segmented gold pyramid with a size-adjustable nanopyramid end, which is capable of supporting monopole localized surface plasmon resonance (LSPR) modes leading to high spectral enhancement when its resonance energy is matched with the excitation laser energy. Here, we describe in detail the PTTP fabrication method and report a statistical analysis based on 530 PTTPs' and 185 ordinary gold micropyramids' templates. Our results indicate that the PTTP method generates probes with an apex diameter smaller than 30 nm on 92.4% of the batch, which is a parameter directly related to the achievable TERS spatial resolution. Moreover, the PTTPs' nanopyramid edge size L, a critical parameter for LSPR spectral tuning, shows variability typically smaller than 12.5%. The PTTP's performance was tested in TERS experiments performed on graphene, and the results show a spectral enhancement of up to 72-fold, which is at least one order of magnitude higher than that typically achieved with gold micropyramids. Imaging resolution is in the order of 20 nm.

12.
Nano Lett ; 20(2): 953-962, 2020 Feb 12.
Artículo en Inglés | MEDLINE | ID: mdl-31869233

RESUMEN

While various electronic components based on carbon nanotubes (CNTs) have already been demonstrated, the realization of miniature electromagnetic coils based on CNTs remains a challenge. Coils made of single-wall CNTs with accessible ends for contacting have been recently demonstrated but were found unsuitable to act as electromagnetic coils because of electrical shorting between their turns. Coils made of a few-wall CNT could in principle allow an insulated flow of current and thus be potential candidates for realizing CNT-based electromagnetic coils. However, no such CNT structure has been produced so far. Here, we demonstrate the formation of few-wall CNT coils and characterize their structural, optical, vibrational, and electrical properties using experimental and computational tools. The coils are made of CNTs with 2, 3, or 4 walls. They have accessible ends for electrical contacts and low defect densities. The coil diameters are on the order of one micron, like those of single-wall CNT coils, despite the higher rigidity of few-wall CNTs. Coils with as many as 163 turns were found, with their turns organized in a rippled raft configuration. These coils are promising candidates for a variety of miniature devices based on electromagnetic coils, such as electromagnets, inductors, transformers, and motors. Being chirally and enantiomerically pure few-wall CNT bundles, they are also ideal for fundamental studies of interwall coupling and superconductivity in CNTs.

13.
Analyst ; 144(23): 7049-7056, 2019 Nov 18.
Artículo en Inglés | MEDLINE | ID: mdl-31657367

RESUMEN

The global prevalence of Alzheimer's disease (AD) points to endemic levels, especially considering the increase of average life expectancy worldwide. AD diagnosis based on early biomarkers and better knowledge of related pathophysiology are both crucial in the search for medical interventions that are able to modify AD progression. In this study we used unsupervised spectral unmixing statistical techniques to identify the vibrational spectral signature of amyloid ß aggregation in neural tissues, as early biomarkers of AD in an animal model. We analyzed spectral images composed of a total of 55 051 Raman spectra obtained from the frontal cortex and hippocampus of five bitransgenic APPswePS1ΔE9 mice, and colocalized amyloid ß plaques by other fluorescence techniques. The Raman signatures provided a multifrequency fingerprint consistent with the results of synthesized amyloid ß fibrils. The fingerprint obtained from unmixed analysis in neural tissues is shown to provide a detailed image of amyloid plaques in the brain, with the potential to be used as biomarkers for non-invasive early diagnosis and pathophysiology studies in AD on the retina.


Asunto(s)
Enfermedad de Alzheimer/diagnóstico por imagen , Amiloide/análisis , Placa Amiloide/diagnóstico por imagen , Enfermedad de Alzheimer/patología , Secretasas de la Proteína Precursora del Amiloide/genética , Animales , Lóbulo Frontal/patología , Hipocampo/patología , Ratones Transgénicos , Presenilina-1/genética , Espectrometría Raman/métodos
14.
Nano Lett ; 19(10): 7357-7364, 2019 10 09.
Artículo en Inglés | MEDLINE | ID: mdl-31469281

RESUMEN

The knowledge of the phonon coherence length is of great importance for two-dimensional-based materials since phonons can limit the lifetime of charge carriers and heat dissipation. Here we use tip-enhanced Raman spectroscopy (TERS) to measure the spatial correlation length Lc of the A1g1 and A1g2 phonons of monolayer and few-layer gallium sulfide (GaS). The differences in Lc values are responsible for different enhancements of the A1g modes, with A1g1 always enhancing more than the A1g2, independently of the number of GaS layers. For five layers, the results show an Lc of 64 and 47 nm for A1g1 and A1g2, respectively, and the coherence lengths decrease when decreasing the number of layers, indicating that scattering with the surface roughness plays an important role.

15.
Phys Rev Lett ; 119(19): 193603, 2017 Nov 10.
Artículo en Inglés | MEDLINE | ID: mdl-29219533

RESUMEN

The microscopic theory of superconductivity raised the disruptive idea that electrons couple through the elusive exchange of virtual phonons, overcoming the strong Coulomb repulsion to form Cooper pairs. Light is also known to interact with atomic vibrations, as, for example, in the Raman effect. We show that photon pairs exchange virtual vibrations in transparent media, leading to an effective photon-photon interaction identical to that for electrons in the BCS theory of superconductivity, in spite of the fact that photons are bosons. In this scenario, photons may exchange energy without matching a quantum of vibration of the medium. As a result, pair correlations for photons scattered away from the Raman resonances are expected to be enhanced. An experimental demonstration of this effect is provided here by time-correlated Raman measurements in different media. The experimental data confirm our theoretical interpretation of a photonic Cooper pairing, without the need for any fitting parameters.

16.
Nat Nanotechnol ; 12(12): 1176-1182, 2017 12.
Artículo en Inglés | MEDLINE | ID: mdl-28967894

RESUMEN

Double-walled carbon nanotubes (DWCNTs) consist of two coaxially aligned single-walled carbon nanotubes (SWCNTs), and previous sorting methods only achieved outer-wall electronic-type selectivity. Here, a separation technique capable of sorting DWCNTs by semiconducting (S) or metallic (M) inner- and outer-wall electronic type is presented. Electronic coupling between the inner and outer wall is used to alter the surfactant coating around each of the DWCNT types, and aqueous gel permeation is used to separate them. Aqueous methods are used to remove SWCNT species from the raw material and prepare enriched DWCNT fractions. The enriched DWCNT fractions are then transferred into either chlorobenzene or toluene using the copolymer PFO-BPy to yield the four inner@outer combinations of M@M, M@S, S@M and S@S. The high purity of the resulting fractions is verified by absorption measurements, transmission electron microscopy, atomic force microscopy, resonance Raman mapping and high-density field-effect transistor devices.

17.
Nano Lett ; 17(6): 3447-3451, 2017 06 14.
Artículo en Inglés | MEDLINE | ID: mdl-28541053

RESUMEN

In this work we probe the third-order nonlinear optical property of graphene and hexagonal boron nitride and their heterostructure by the use of coherent anti-Stokes Raman spectroscopy. When the energy difference of the two input fields matches the phonon energy, the anti-Stokes emission intensity is enhanced in h-BN, as usually expected, while for graphene an anomalous decrease is observed. This behavior can be understood in terms of a coupling between the electronic continuum and a discrete phonon state. We have also measured a graphene/h-BN heterostructure and demonstrate that the anomalous effect in graphene dominates the heterostructure nonlinear optical response.

18.
J Nanobiotechnology ; 15(1): 26, 2017 Apr 04.
Artículo en Inglés | MEDLINE | ID: mdl-28376812

RESUMEN

BACKGROUND: Dengue is the most prevalent arthropod-borne viral disease in the world. In this article we present results on the development, characterization and immunogenic evaluation of an alternative vaccine candidate against Dengue. METHODS: The MWNT-DENV3E nanoconjugate was developed by covalent functionalization of carboxylated multi-walled carbon nanotubes (MWNT) with recombinant dengue envelope (DENV3E) proteins. The recombinant antigens were bound to the MWNT using a diimide-activated amidation process and the immunogen was characterized by TEM, AFM and Raman Spectroscopy. Furthermore, the immunogenicity of this vaccine candidate was evaluated in a murine model. RESULTS: Immunization with MWNT-DENV3E induced comparable IgG responses in relation to the immunization with non-conjugated proteins; however, the inoculation of the nanoconjugate into mice generated higher titers of neutralizing antibodies. Cell-mediated responses were also evaluated, and higher dengue-specific splenocyte proliferation was observed in cell cultures derived from mice immunized with MWNT-DENV3E when compared to animals immunized with the non-conjugated DENV3E. CONCLUSIONS: Despite the recent licensure of the CYD-TDV dengue vaccine in some countries, results from the vaccine's phase III trial have cast doubts about its overall efficacy and global applicability. While questions about the effectiveness of the CYD-TDV vaccine still lingers, it is wise to keep at hand an array of vaccine candidates, including alternative non-classical approaches like the one presented here.


Asunto(s)
Formación de Anticuerpos , Vacunas contra el Dengue/inmunología , Dengue/prevención & control , Nanotubos de Carbono/química , Proteínas del Envoltorio Viral/inmunología , Animales , Anticuerpos Neutralizantes/sangre , Anticuerpos Antivirales/sangre , Antígenos Virales/inmunología , Proliferación Celular , Citocinas/inmunología , Dengue/inmunología , Vacunas contra el Dengue/uso terapéutico , Virus del Dengue/inmunología , Femenino , Inmunidad Celular , Inmunoglobulina G/sangre , Ratones , Ratones Endogámicos BALB C , Microscopía de Fuerza Atómica , Microscopía Electrónica de Transmisión , Nanoconjugados/química , Nanomedicina , Proteínas Recombinantes/química , Proteínas Recombinantes/inmunología , Espectrometría Raman , Bazo/citología , Vacunas de Subunidad/inmunología , Vacunas de Subunidad/uso terapéutico
19.
Phys Rev Lett ; 117(24): 243603, 2016 Dec 09.
Artículo en Inglés | MEDLINE | ID: mdl-28009217

RESUMEN

Water is one of the most prevalent chemicals on our planet, an integral part of both our environment and our existence as a species. Yet it is also rich in anomalous behaviors. Here we reveal that water is a novel-yet ubiquitous-source for quantum correlated photon pairs at ambient conditions. The photon pairs are produced through Raman scattering, and the correlations arise from the shared quantum of a vibrational mode between the Stokes and anti-Stokes scattering events. We confirm the nonclassical nature of the produced photon pairs by showing that the cross-correlation and autocorrelations of the signals violate a Cauchy-Schwarz inequality by over 5 orders of magnitude. The unprecedented degree of violating the inequality in pure water, as well as the well-defined polarization properties of the photon pairs, points to its usefulness in quantum information.

20.
Sci Rep ; 6: 33588, 2016 09 19.
Artículo en Inglés | MEDLINE | ID: mdl-27642034

RESUMEN

The pellucid zone (PZ) is a protective embryonic cells barrier against chemical, physical or biological substances. This put, usual transfection methods are not efficient for mammal oocytes and embryos as they are exclusively for somatic cells. Carbon nanotubes have emerged as a new method for gene delivery, and they can be an alternative for embryos transfection, however its ability to cross the PZ and mediated gene transfer is unknown. Our data confirm that multiwall carbon nanotubes (MWNTs) can cross the PZ and delivery of pDNA into in vitro-fertilized bovine embryos. The degeneration rate and the expression of genes associated to cell viability were not affected in embryos exposed to MWNTs. Those embryos, however, had lower cell number and higher apoptotic cell index, but this did not impair the embryonic development. This study shows the potential utility of the MWNT for the development of new method for delivery of DNA into bovine embryos.


Asunto(s)
Blastocisto/metabolismo , ADN/administración & dosificación , Técnicas de Transferencia de Gen , Nanotubos de Carbono , Animales , Bovinos , Técnicas de Cultivo de Célula , Células Cultivadas , Femenino , Genes Reporteros , Nanotubos de Carbono/química , Nanotubos de Carbono/ultraestructura , Técnicas de Transferencia Nuclear , Plásmidos/administración & dosificación , Plásmidos/genética , Embarazo
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