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1.
Nano Lett ; 24(14): 4072-4081, 2024 Apr 10.
Artigo em Inglês | MEDLINE | ID: mdl-38557078

RESUMO

Given the binary nature of nanoalloy systems, their properties are dependent on their size, shape, structure, composition, and chemical ordering. When energy and entropic factors for shapes and structure variations are considered in nanoparticle growth, the spectra of shapes become so vast that even metastable arrangements have been reported under ambient conditions. Experimental and theoretical variations of multiply twinned particles have been observed, from the Ino and Marks decahedra to polyicosahedra and polydecahedra with comparable energetic stability among them. Herein, we report the experimental production of a stable doubly truncated double-icosahedron structure (TdIh) in Au-Ag nanoparticles, in which a twinned Ag-rich alloyed shell is reconstructed on a Au-Ag alloyed Ino-decahedral core. The structure, chemical composition, and growth pathway are proposed on the basis of high-angle annular dark-field scanning transmission electron microscopy analysis and excess energy calculations, while its structural stability is estimated by large-scale atomic molecular dynamics simulations. This novel nanostructure differs from other structures previously reported.

2.
Int J Mol Sci ; 23(22)2022 Nov 11.
Artigo em Inglês | MEDLINE | ID: mdl-36430385

RESUMO

Extensive burns represent a significant challenge in biomedicine due to the multiple systemic and localized complications resulting from the major skin barrier loss. The functionalization of xenografts with nanostructured antibacterial agents proposes a fast and accessible application to restore barrier function and prevent localized bacterial contamination. Based on this, the objective of this work was to functionalize a xenograft by electrospray deposition with silver nanoparticles (AgNPs) and to evaluate its antibiofilm and cytotoxic effects on human fibroblasts. Initially, AgNPs were synthesized by a green microwave route with sizes of 2.1, 6.8, and 12.2 nm and concentrations of 0.055, 0.167, and 0.500 M, respectively. The AgNPs showed a size relationship directly proportional to the concentration of AgNO3, with a spherical and homogeneous distribution determined by high-resolution transmission electron microscopy. The surface functionalization of radiosterilized porcine skin (RPS) via electrospray deposition with the three AgNP concentrations (0.055, 0.167, and 0.500 M) in the epidermis and the dermis showed a uniform distribution on both surfaces by energy-dispersive X-ray spectroscopy. The antibiofilm assays of clinical multidrug-resistant Pseudomonas aeruginosa showed significant effects at the concentrations of 0.167 and 0.500 M, with a log reduction of 1.3 and 2.6, respectively. Additionally, viability experiments with human dermal fibroblasts (HDF) exposed to AgNPs released from functionalized porcine skin showed favorable tolerance, with retention of viability more significant than 90% for concentrations of 0.05 and 0.167 M after 24 h exposure. Antibacterial activity combined with excellent biocompatibility makes this biomaterial a candidate for antibacterial protection by inhibiting bacterial biofilms in deep burns during early stages of development.


Assuntos
Queimaduras , Nanopartículas Metálicas , Humanos , Suínos , Prata/química , Nanopartículas Metálicas/uso terapêutico , Nanopartículas Metálicas/química , Antibacterianos/farmacologia , Antibacterianos/uso terapêutico , Antibacterianos/química , Biofilmes , Bactérias , Queimaduras/tratamento farmacológico
3.
Nanotechnology ; 32(9): 095705, 2021 Feb 26.
Artigo em Inglês | MEDLINE | ID: mdl-33202386

RESUMO

Antimony selenide (Sb2Se3) is a material widely used in photodetectors and relatively new as a possible material for thermoelectric applications. Taking advantage of the new properties after nanoscale fabrication, this material shows great potential for the development of efficient low temperature thermoelectric devices. Here we study the synthesis, the crystal properties and the thermal and thermoelectric transport response of Sb2Se3 hexagonal nanotubes (HNT) in the temperature range between 120 and 370 K. HNT have a moderate electrical conductivity ∼102 S m-1 while maintaining a reasonable Seebeck coefficient ∼430 µV K-1 at 370 K. The electrical conductivity in Sb2Se3 HNT is about 5 orders of magnitude larger and its thermal conductivity one half of what is found in bulk. Moreover, the calculated figure of merit (ZT) at room temperature is the largest value reported in antimony selenide 1D structures.

4.
Nanotechnology ; 30(1): 014001, 2019 Jan 04.
Artigo em Inglês | MEDLINE | ID: mdl-30277886

RESUMO

Semiconductors with magnetic response at room temperature are sought for spintronics in solid-state devices. Among possible materials for this applications, the magnetic response of FeSi and doped FeSi have produced contradictory results at the nanoscale and more precise measurements and deeper studies are needed to clarify its potential capabilities. For that reason, in this work, single nanowire measurements of ferromagnetic semiconducting FeSi and Mn-doped FeSi nanostructures have been performed using magnetic force microscopy and electron holography. Results obtained confirm the presence of magnetic domains at room temperature with a magnetic moment per Fe atom of [Formula: see text] Spin polarized density functional calculations confirm a net magnetic moment between [Formula: see text] in Fe surface atoms with an estimated Curie temperature of 417 K by means of the molecular field approximation. The nanowires present a crystalline B20 cubic structure as confirmed by x-ray diffraction and high-resolution electron microscopy. Their electrical transport measurements confirm p-type nature and thermal activation. A remanent magnetization of 1.5 × 10-5 emu and 0.5 × 10-5 emu was measured at room temperature for FeSi and Mn-doped FeSi respectively, with spin freezing behavior around 30 K for the Mn-doped nanowires.

5.
Nanotechnology ; 30(42): 425701, 2019 Oct 18.
Artigo em Inglês | MEDLINE | ID: mdl-31174202

RESUMO

The idea that shape and structure determines functionality is one of the leiv-motifs that drives research and applications on fields such as catalysis and plasmonics. The growth and stability of metallic clusters is extensively discussed through faceting and energy minimization mechanisms, respectively. Facet truncations on the regular Mackay-icosahedron (m-Ih) give rise to two sub-families exhibiting five-fold symmetry and external decahedral shape. Such successive truncations made to the regular m-Ih, led to a decahedral motif called 'Decmon' (Montejano's decahedron). This structure expose facets (111) and (100), that after a total energy minimization through molecular dynamics simulations using the embedded atom model, proved to be thermally stable. This result has been confirmed by using nano-thermodynamics. The surface energy competition between the (111) and (100) facets explains its stability at some given cluster sizes, and this truncation path permits to glimpse the potential energy surface in the growth path of nanoparticles from the decahedral (s-Dh) to icosahedral (m-Ih) structures.

6.
Nanotechnology ; 30(20): 205701, 2019 May 17.
Artigo em Inglês | MEDLINE | ID: mdl-30673656

RESUMO

Anisotropic gold nanoparticles offer potential applications due to their functionalities and shape-dependent properties. Reshaping noble metal nanoparticles is an interesting field with optical, surface-enhanced Raman spectroscopy, catalytic applications and potential application as a photothermic therapy. This work comprises a structural study on gold nano bipyramids (Au NBPs) and nanodumbbells, and the evolution of Au NBPs capped with cetyltrimethylammonium bromide and dodecanethiol through an in situ and ex situ heating process in high vacuum. Also, we study the reshaping of Au NBPs by the addition of Pt to study the surface modification and the strain generated on a single particle by geometric phase analysis.

7.
Phys Chem Chem Phys ; 21(44): 24731-24739, 2019 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-31681939

RESUMO

We report a combined experimental/theoretical approach to study the connection of S-vacancies and wrinkling on MoS2 layers, and how this feature produces significant changes in the electronic structure and reactivity of this 2D material. The MoS2 material, when used as a catalyst in operative conditions, was found to be mainly composed of thin and short 1-5 layer sheets instead of a poorly crystalline structure, as it was previously assumed. Notably wrinkled structures with S-vacancies were also found through transmission electron microscopy. Atomistic simulations revealed a natural connection between sulfur-vacancies, wrinkling and folding. Density functional calculations further revealed that such curved structures present a lower electronic band-gap and a higher reactivity towards thiophene compared to the planar MoS2 counterpart.

8.
Oral Dis ; 25(6): 1627-1633, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31177594

RESUMO

OBJECTIVES: To compare the sialic acid (SA) levels in saliva among periodontitis-affected, gingivitis and control patients. METHODS: The study involved 93 subjects. The participants were divided into three groups: (1) 30 subjects without periodontal disease (control group); (2) 30 subjects with gingivitis; and (3) 33 subjects with periodontitis. The oral parameters examined were as follows: (a) Simplified Oral Hygiene Index; (b) Calculus Index; (c) Gingival Index; (d) probing pocket depth; and (e) level of epithelial attachment. SA levels in saliva were measured by means of surface-enhanced Raman spectroscopy (SERS). This method has demonstrated the capacity to detect extremely low concentrations of molecules. The spectrum was calibrated using analytical reagent SA. RESULTS: The obtained median values for SA concentrations were 5.98, 7.32, and 17.12 mg/dl for control, gingivitis, and periodontitis patients, respectively. CONCLUSIONS: Our measurements by SERS corroborate that in periodontitis-affected patients, the SA concentration is larger than their concentrations in either control or gingivitis patients. This confirms previous reports and opens the possibility of using SERS as a diagnostic tool.


Assuntos
Ácido N-Acetilneuramínico/análise , Periodontite/diagnóstico , Saliva/química , Adulto , Feminino , Gengivite , Humanos , Masculino , Pessoa de Meia-Idade , Ácido N-Acetilneuramínico/química , Índice Periodontal , Saliva/metabolismo , Análise Espectral Raman
9.
Langmuir ; 34(32): 9394-9401, 2018 08 14.
Artigo em Inglês | MEDLINE | ID: mdl-30011365

RESUMO

We report the efficient wet-chemical production of self-assembled gold-copper bimetallic nanoparticles (diameter of ∼2 nm) into two-dimensional flexible ribbonlike nanostructures. The direct observation of a layered arrangement of particles into nanoribbons was provided through high-resolution transmission electron microscopy and electron tomography. These nanoribbons showed photoluminesce and efficient photocatalytic activity for the conversion of 4-nitrophenol. The thermal stability of the nanoribbons was also measured by in situ heat treatment in the electron microscope, confirming that the self-assembled gold-copper nanoribbons efficiently supported up to 350 °C. The final morphology of the nanoparticles and their ability to self-assemble into flexible nanoribbons were dependent on concentration and the ratio of precursors. Therefore, these experimental factors were discussed. Remarkably, the presence of copper was found to be critical to triggering the self-assembly of nanoparticles into ordered layered structures. These results for the synthesis and stability of self-assemblies of metallic nanoparticles present a potential extension of the method to producing materials with catalytic applications.

14.
Nanotechnology ; 29(12): 125607, 2018 03 23.
Artigo em Inglês | MEDLINE | ID: mdl-29431153

RESUMO

We report the synthesis of MWNT/ZnO hybrid nanostructures. A simple, affordable, chemical procedure to functionalize MWNTs with ZnO nanoparticles was performed. A significant portion of the surface of MWNTs was covered with ZnO nanoparticles; these particles formed highly porous spherical nodules of 50-150 nm in diameter, sizes that are an order of magnitude larger than similar ZnO nanonodules reported in the literature. Hence, the self-assembled nanocomposite the ZnO exhibited a large surface-to-volume ratio, which is a very advantageous property for potential catalytic applications. The resultant MWNT/ZnO nanocomposites were characterized by x-ray diffraction, scanning and high-resolution transmission electron microscopy, and UV-vis and Raman spectroscopy. The temperature coefficient of resistance (TCR) of the nanocomposites was measured and reported. The average TCR value goes from -5.6%/K up to -18%/K, over temperature change intervals from 10 K to 1 K. Based on these TCR results, the nanocomposite MWNT/ZnO prepared in this work is a promising material, with potential application as a bolometric sensor.

15.
Nano Lett ; 16(3): 1568-73, 2016 Mar 09.
Artigo em Inglês | MEDLINE | ID: mdl-26849249

RESUMO

In this work, we report the synthesis and detailed structural characterization of novel helical gold-copper nanowires. The nanowires possess the Boerdijk-Coxeter-Bernal structure, based on the pile up of octahedral, icosahedral, and/or decahedral seeds. They are self-assembled into a coiled manner as individual wires or into a parallel-ordering way as groups of wires. The helical nanowires are ultrathin with a diameter of less than 10 nm and variable length of several micrometers, presenting a high density of twin boundaries and stacking faults. To the best of our knowledge, such gold-copper nanowires have never been reported previously.


Assuntos
Cobre/química , Ouro/química , Nanofios/ultraestrutura , Aminas/química , Glucose/química , Modelos Moleculares , Nanotecnologia/métodos , Nanofios/química
16.
Cell Immunol ; 295(2): 83-91, 2015 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-25863744

RESUMO

The human pathogen Chlamydia pneumoniae has been implicated in chronic inflammatory diseases including type 2 diabetes. Therefore, we designed a study to evaluate pancreatic beta cells and mast cells during chlamydial infection. Our study revealed that C. pneumoniae infected mast cells significantly (p<0.005) decreased beta cell ATP and insulin production, in contrast to uninfected mast cells co-cultured with beta cells. Infected mast cells exhibited pyknotic nuclei and active caspase-3 and caspase-1 expression. Additionally, ex vivo analyses of tissues collected from C. pneumoniae infected mice showed increased interleukin-1ß production in splenocytes and pancreatic tissues as was observed with in vitro mast cell-beta cell co-cultures during C. pneumoniae infection. Notably, infected mast cells promoted beta cell destruction. Our findings reveal the negative effect of C. pneumoniae on mast cells, and the consequential impact on pancreatic beta cell function and viability.


Assuntos
Infecções por Chlamydia/imunologia , Chlamydophila pneumoniae/imunologia , Diabetes Mellitus Tipo 2/microbiologia , Células Secretoras de Insulina/microbiologia , Mastócitos/microbiologia , Animais , Caspase 1/análise , Caspase 3/análise , Sobrevivência Celular/imunologia , Infecções por Chlamydia/microbiologia , Técnicas de Cocultura , Diabetes Mellitus Tipo 2/imunologia , Citometria de Fluxo , Células Secretoras de Insulina/imunologia , Interleucina-1beta/análise , Fígado/citologia , Mastócitos/imunologia , Camundongos Endogâmicos C57BL , Camundongos Obesos , Microscopia Confocal , Microscopia Eletrônica de Varredura , Organismos Livres de Patógenos Específicos , Baço/citologia
17.
Opt Express ; 23(19): 25111-7, 2015 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-26406710

RESUMO

Nanoantennas have been fabricated by scaling down traditional antenna designs using nanolithographic techniques and testing them at different optical wavelengths, these particular nanoantennas have shown responses in a broad range of frequencies going from visible wavelengths to the range of the terahertz. Some self-assembled nanostructures exist that exhibit similar shapes and properties to those of traditional antenna structures. In this work the emission and absorption properties of self-assembled nanostructures made of zinc oxide nanorods on silver nanowires, which resemble traditional dipole antennas, were measured and simulated in order to test their antenna performance. These structures show resonant properties in the 10-120 THz range, with the main resonance at 60 THz. The radiation pattern of these nanostructures was also obtained by numerical simulations, and it is shown that it can be tailored to increase or decrease its directivity as a function of the location of the energy source of excitation. Experimental measurements were performed by Raman spectroscopy and Fourier Transform Infrared Spectroscopy (FTIR) in order to show existing vibrational frequencies at the resonant frequencies of the nanostructures, measurements were made from ~9 to 103 THz and the results were in agreement with the simulations. These characteristics make these metal-semiconductor Ag/ZnO nanostructures useful as self-assembled nanoantennas in applications such as terahertz spectroscopy and sensing at terahertz frequencies.


Assuntos
Teste de Materiais , Metais/química , Nanotecnologia/métodos , Optometria/métodos , Óxido de Zinco/química , Nanoestruturas/química , Tamanho da Partícula , Semicondutores , Análise Espectral Raman , Vibração
18.
Langmuir ; 31(11): 3527-36, 2015 Mar 24.
Artigo em Inglês | MEDLINE | ID: mdl-25742562

RESUMO

Gold nanoparticles with anisotropic structures have tunable absorption properties and diverse bioapplications as image contrast agents, plasmonics, and therapeutic-diagnostic materials. Amino acids with electrostatically charged side chains possess inner affinity for metal ions. Lysine (Lys) efficiently controlled the growing into star-shape nanoparticles with controlled narrow sizes (30-100 nm) and produced in high yields (85-95%). Anisotropic nanostructures showed tunable absorbance from UV to NIR range, with extraordinary colloidal stability (-26 to -42 mV) and surface-enhanced Raman scattering properties. Advanced electron microscopy characterization through ultra-high-resolution SEM, STEM, and HR-TEM confirmed the size, nanostructure, crystalline structure, and chemical composition. Molecular dynamics simulations revealed that Lys interacted preferentially with Au(I) through the -COOH group instead of their positive side chains with a binding free energy (BFE) of 3.4 kcal mol(-1). These highly monodisperse and colloidal stable anisotropic particles prepared with biocompatible compounds may be employed in biomedical applications.


Assuntos
Ouro/química , Nanopartículas Metálicas/química , Anisotropia , Coloides/química
19.
J Nanobiotechnology ; 13: 91, 2015 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-26666378

RESUMO

BACKGROUND: Candida albicans is the most common pathogenic fungus isolated in bloodstream infections in hospitalized patients, and candidiasis represents the fourth most common infection in United States hospitals, mostly due to the increasing numbers of immune- and medically-compromised patients. C. albicans has the ability to form biofilms and morphogenetic conversions between yeast and hyphal morphologies contribute to biofilm development and represent an essential virulence factor. Moreover, these attached communities of cells are surrounded by a protective exopolymeric matrix that effectively shelters Candida against the action of antifungals. Because of dismal outcomes, novel antifungal strategies, and in particular those targeting biofilms are urgently required. As fungi are eukaryotic, research and development of new antifungal agents has been difficult due to the limited number of selective targets, also leading to toxicity. RESULTS: By microwave-assisted techniques we obtained pure 1 nm spherical silver nanoparticles ideal for their potential biological applications without adding contaminants. A phenotypic assay of C. albicans demonstrated a potent dose-dependent inhibitory effect of silver nanoparticles on biofilm formation, with an IC50 of 0.089 ppm. Also silver nanoparticles demonstrated efficacy when tested against pre-formed C. albicans biofilms resulting in an IC50 of 0.48 ppm. The cytotoxicity assay resulted in a CC50 of 7.03 ppm. The ultrastructural differences visualized under SEM with silver nanoparticles treatment were changes in the surface appearance of the yeast from smooth to rough thus indicating outer cell wall damage. On the fungal pre-formed biofilm true hyphae was mostly absent, as filamentation was inhibited. TEM measurement of the cell-wall width of C. albicans after treatment resulted in significant enlargement (206 ± 11 nm) demonstrating membrane permeabilization. CONCLUSIONS: Our results demonstrate that silver nanoparticles are potent inhibitors of C. albicans biofilm formation. SEM observations are consistent with an overall loss of structure of biofilms mostly due to disruption of the outer cell membrane/wall and inhibition of filamentation.TEM indicates the permeabilization of the cell wall and subsequent disruption of the structural layers of the outer fungal cell wall. The anti-biofilm effects are via cell wall disruption.


Assuntos
Biofilmes/efeitos dos fármacos , Candida albicans/fisiologia , Candida albicans/ultraestrutura , Nanopartículas Metálicas/química , Nanopartículas Metálicas/ultraestrutura , Prata/farmacologia , Candida albicans/efeitos dos fármacos , Fenótipo , Plâncton/efeitos dos fármacos , Plâncton/ultraestrutura , Espectrometria por Raios X , Temperatura
20.
Nano Lett ; 14(11): 6718-26, 2014 Nov 12.
Artigo em Inglês | MEDLINE | ID: mdl-25338111

RESUMO

Gold-copper (Au-Cu) phases were employed already by pre-Columbian civilizations, essentially in decorative arts, whereas nowadays, they emerge in nanotechnology as an important catalyst. The knowledge of the phase diagram is critical to understanding the performance of a material. However, experimental determination of nanophase diagrams is rare because calorimetry remains quite challenging at the nanoscale; theoretical investigations, therefore, are welcomed. Using nanothermodynamics, this paper presents the phase diagrams of various polyhedral nanoparticles (tetrahedron, cube, octahedron, decahedron, dodecahedron, rhombic dodecahedron, truncated octahedron, cuboctahedron, and icosahedron) at sizes 4 and 10 nm. One finds, for all the shapes investigated, that the congruent melting point of these nanoparticles is shifted with respect to both size and composition (copper enrichment). Segregation reveals a gold enrichment at the surface, leading to a kind of core-shell structure, reminiscent of the historical artifacts. Finally, the most stable structures were determined to be the dodecahedron, truncated octahedron, and icosahedron with a Cu-rich core/Au-rich surface. The results of the thermodynamic approach are compared and supported by molecular-dynamics simulations and by electron-microscopy (EDX) observations.


Assuntos
Cobre/química , Ligas de Ouro/química , Nanopartículas Metálicas/química , Nanopartículas Metálicas/ultraestrutura , Simulação de Dinâmica Molecular , Nanotecnologia , Tamanho da Partícula , Transição de Fase , Termodinâmica
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