Structural, Optical and Catalytic Properties of Bimetallic and Metal-Semiconductor Nanorods

Metal and semiconductor nanomaterials exhibit highly tunable electric, magnetic, optical and catalytic properties. To obtain desired properties, structure and composition of the nanomaterials must be fine-tuned, which requires fundamental understanding of the growth mechanism. In the thesis research, we study Au-Cu alloy nanorods (NRs) growth mechanism using single particle scattering spectroscopy. From electrodynamics simulations, it was revealed that the unusual features of the single particle scattering spectra were due to atomic level structural defects made up of few atoms on the surface of NRs, caused by galvanic replacement reaction (GRR). NRs are further explored as templates for GRR using HAuCl4. Interestingly, NRs transformed into hollow rods or break into nanospheres via a hollow junction dumbbell shaped intermediate, at different concentrations of HAuCl4. The hollow rods showed enhanced catalytic activity for p-nitrophenol reduction, while dumbbell shaped intermediates displayed junction dependent optical properties. Later plasmon-exciton interactions in Ag-CdS hybrid nanorods were explored. The absorption studies revealed mixed electronic states at the metal semiconductor interface while the CdS length dependent photoluminescence displayed by hybrid nanorods was trap state emission. Our detailed studies of the structural transformation mechanisms and corresponding optical properties provide guidance to fabricate nanomaterials with tunable structure and compositions for exciting applications

Padronização da pesquisa de linfonodos sentinelas em estômago por métodos combinados

Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Ciências Médicas, Pós-Graduação em Ciências da Cirurgia, Campinas, 2012.Introdução - Com os estudos de Gould et al. (1960), Cabanas (1977) e Morton et al. (1992), estabeleceu-se o conceito da pesquisa do linfonodo sentinela. Esse se baseia na teoria de que ao identificar a presença ou ausência de metástase no primeiro linfonodo que recebe a drenagem linfática a partir do tumor (sentinela), poderia representar o estado de acometimento dos outros linfonodos. Isto evitaria a realização desnecessária de linfadenectomias. Com o passar dos anos, foi consagrada para ser aplicada em casos de melanoma e câncer de mama. Nesta última década, tenta-se estender os princípios da utilização da pesquisa de linfonodo sentinela para os cânceres do aparelho digestivo. Entretanto, no caso do estômago, existem algumas dificuldades, como: presença de sistema de drenagem linfática multidirecional, ocorrência de metástases saltatórias e identificação de mais de um linfonodo sentinela por indivíduo. Objetivo - Criar e padronizar um modelo animal para o treinamento de pesquisa de linfonodos sentinelas em estômago. Método - Trinta e dois coelhos, saudáveis, foram submetidos à anestesia exclusivamente intramuscular. Por meio de laparotomia, foi injetado na subserosa da parede anterior do corpo gástrico, 0,1 ml de fitato marcado com tecnécio-99m (0,2 mCi), em seguida pelo mesmo orifício, de 0,2 ml de Azul Patente V® 2,5%. A cavidade abdominal foi avaliada, in vivo , para pesquisa de suspeitas de linfonodos azuis (corados em azul) e com detector manual de radiação gamma aos 5, 10 e 20 minutos para detecção de suspeitas de linfonodos radioativos (radioatividade identificada superior a 10X o valor apresentado pelo fundo). Após 20 minutos, realizou-se ressecção e exérese total do estômago, baço e suspeitas de linfonodos, para posterior avaliação da radioatividade ex vivo . A seguir, encaminharam-se as suspeitas de linfonodos para estudo histológico para identificação de tecido linfóide. Resultados - Foram identificados linfonodos em 30 coelhos (93,75%) com média de 2,2 por animal. Das 90 suspeitas de linfonodos detectadas, em 70 casos (77,77%) obteve-se confirmação histológica para tecido linfóide. Dessas, a maioria foi identificada e localizada na região entre o esôfago e o fundo gástrico durante a avaliação in vivo aos 5 minutos. Dois coelhos faleceram durante os experimentos (Taxa de mortalidade = 6,25%). Conclusão - O modelo experimental em coelhos para pesquisa de linfonodos sentinelas em estômago por métodos combinados foi factível, de fácil execução e baixa mortalidade, podendo ser usado para treinamento.Abstract : Introduction - The concept of sentinel lymph node was established by the studies of Gould et al. (1960), Cabanas (1977) and Morton et al. (1992). It is based on the theory that, whenever the presence or absence of metastasis is identified in the first lymph node that receives the lymphatic drainage from the tumor (sentinel) the status of involvement of other lymph nodes might be infered. This could avoid the performance of unnecessary lymphadenectomies. Over the years, its use was consecrated by its application in melanoma and breast cancer. In the last decade, attempts have been made to extend the principles of sentinel lymph node investigation to cancers of the digestive tract. In the case of stomach cancer, additional difficulties were found, such as multiple and aberrant lymphatic routes, the occurrence of skip metastasis and the possible identification of more than one sentinel lymph node in the same patient. Aim - To develop and evaluate an animal model for training sentinel lymph node navigation in the stomach. Methods - Thirtytwo healthy rabbits, were prepped and given intramuscular anesthesia. Through a formal laparotomy, they received a subserosal injection of 0.1 ml of phytate labeled with technetium-99m (0.2 mCi) in the anterior wall of the gastric corpus, followed by 0.2 ml of Blue Patent ® V 2.5%, through the same puncture site. Suspicious lymph nodes were searched in-vivo at 5, 10 and 20 minutes, both visually (Blue Patent stained lymph nodes) and with a manual gamma radiation detector (to detect suspected radioactive lymph nodes, displaying radioactivity levels over 10X the value displayed by the background). En-block resection of the stomach, spleen, visible limph nodes and local fat tissue was then performed and the specimen was assessed "ex vivo" for radioactivity. Suspected lymph nodes were sent for histological study to evaluate the presence of lymphoid tissue. Results Radiolabeled or stained lymph nodes were identified in 30 rabbits (93.75%) with an average of 2.2 specimens per animal; of the 90 suspicious lymph nodes detected, histology confirmed lymphoid tissue in 70 cases (77.77%). Most lymph nodes were identified at the 5-minute in-vivo evaluation and their most common location was found to be in the region between the esophagus and the gastric fundus. Two rabbits died during the procedure resulting in a 6.25% mortality. Conclusion - The rabbit model proved adequate for training in sentinel node navigation in the stomach by combined methods (dye and radiocolloid) being easy to execute and associated with low mortality

Plasmonic Coupling In Single Silver Nanosphere Assemblies By Polarization-Dependent Dark-Field Scattering Spectroscopy

In this paper, we present an experimental and theoretical study of the plasmonic properties of single Ag nanospheres and the plasmon interactions in assemblies of Ag nanosphere dimers and trimers. High-quality Ag nanospheres with small size distribution are synthesized by etching prefabricated Ag nanocubes. We perform a 360° polarization-resolved scattering study on silver nanosphere dimers and trimers, and correlate the scattering anisotropy with nanoparticle structure through correlated dark-field spectroscopy and scanning electron microscopy (SEM) characterization. The polarization-resolved dimer scattering shows a dipolar pattern aligned with the long axis of the dimer. For single Ag nanosphere trimers assembled in an equilateral triangle geometry, we also observe the dipolar scattering pattern to a certain degree, although the dipolar pattern is not preferentially aligned with any sides of the triangle. Theoretical studies using the T-matrix method reveal that if the Ag nanospheres are perfectly spherical and are assembled in a trimer with D3h symmetry, the scattering spectra should be polarization independent, in contrast to the observed experimental results. The same phenomena are demonstrated in Ag nanopshere assemblies in D4h, D5h, and D6h symmetry as well. Using the discrete dipole approximation method, we find that slight elongation (5%) in one of the three axes of the Ag nanospheres can induce a significant anisotropy in the scattering pattern. We here have shown that even small variations in the nanoparticle geometry that are difficult to resolve with SEM can lead to significant effects in the plasmonic coupling, therefore affecting the scattering spectra of the assembled nanostructures

Formation Of Bimetallic Dumbbell Shaped Particles With A Hollow Junction During Galvanic Replacement Reaction

The galvanic replacement reaction (GRR) has been shown to be an effective method to fine tune the structure of monometallic nanoparticles by controlling the precursor concentration and surface ligands. However, the structural evolution of nanoparticles is not well understood in multimetallic systems, where along with oxidation, dealloying and diffusion occur simultaneously. Here, we demonstrate that by controlling the rate of GRR in AuCu alloy nanorods, they can be transformed into either AuCu hollow rods or AuCu@Au core-shell spheroids. Interestingly, the transformation of rods into spheroids involved a critical intermediate state with a hollow junction and dumbbell shape. The formation of a hollow junction region was attributed to preferential diffusion of Cu atoms to the tips caused by the polycrystallinity and high curvature of the tips of the initial template. This structural transformation was also monitored in situ by single particle scattering spectroscopy. The coupling between the two ends of the dumbbell-shaped intermediate connected with a hollow metallic junction gives rise to additional plasmonic features compared with regular rods. Electrodynamic simulations showed that varying the dimensions of the hollow part by even one nanometer altered the plasmon resonance wavelength and lineshape drastically. This study shows that single particle plasmon resonance can be used as an exquisite tool to probe the internal structure of the nanoscale junctions

Structural Defect Induced Peak Splitting In Gold-Copper Bimetallic Nanorods During Growth By Single Particle Spectroscopy

A single particle level study of bimetallic nanoparticle growth provides valuable information that is usually hidden in ensemble measurements, helping to improve the understanding of a reaction mechanism and overcome the synthetic challenges. In this study, we use single particle spectroscopy to monitor the changes in the scattering spectra of Au-Cu alloy nanorods during growth. We found that the unique features of the single particle scattering spectra were due to atomic level geometric defects in the nanorods. Electrodynamics simulations have demonstrated that small structural defects of a few atomic layers split the scattering peaks, giving rise to higher order modes, which do not exist in defect-free rods of similar geometry. The study shows that single particle scattering technique is as sensitive as high-resolution electron microscopy in revealing atomic level structural defects

Blue-Shifted Narrow Localized Surface Plasmon Resonance From Dipole Coupling In Gold Nanoparticle Random Arrays

In this work, we develop a simple method to produce highly uniform localized surface plasmon resonance (LSPR) substrates based on self-assembly of colloidal gold nanoparticles onto pretreated glass substrates. The LSPR wavelength of the gold nanoparticle arrays is blue-shifted from that of the gold nanoparticles in solution and the single gold nanoparticles on glass substrate. The LSPR width is narrower than that of the single gold nanoparticles. The blue-shifted LSPR is due to the long-range dipole coupling in the gold nanoparticle random arrays indicated from simulations using the T-matrix method. In addition to the popularly used LSPR wavelength dependence on the dielectric environment, we have found that the LSPR width of the gold nanoparticle random arrays is also sensitive to the change in the dielectric environment. The LSPR substrates are reproducible, uniform, and robust with potential applications in LSPR sensing and imaging

Plasmonic Coupling in Single Silver Nanosphere Assemblies by Polarization-Dependent Dark-Field Scattering Spectroscopy

In this paper, we present an experimental and theoretical study of the plasmonic properties of single Ag nanospheres and the plasmon interactions in assemblies of Ag nanosphere dimers and trimers. High-quality Ag nanospheres with small size distribution are synthesized by etching prefabricated Ag nanocubes. We perform a 360° polarization-resolved scattering study on silver nanosphere dimers and trimers, and correlate the scattering anisotropy with nanoparticle structure through correlated dark-field spectroscopy and scanning electron microscopy (SEM) characterization. The polarization-resolved dimer scattering shows a dipolar pattern aligned with the long axis of the dimer. For single Ag nanosphere trimers assembled in an equilateral triangle geometry, we also observe the dipolar scattering pattern to a certain degree, although the dipolar pattern is not preferentially aligned with any sides of the triangle. Theoretical studies using the T-matrix method reveal that if the Ag nanospheres are perfectly spherical and are assembled in a trimer with <i>D</i>_3<i>h</i> symmetry, the scattering spectra should be polarization independent, in contrast to the observed experimental results. The same phenomena are demonstrated in Ag nanopshere assemblies in <i>D</i>_4<i>h</i>, <i>D</i>_5<i>h</i>, and <i>D</i>_6<i>h</i> symmetry as well. Using the discrete dipole approximation method, we find that slight elongation (5%) in one of the three axes of the Ag nanospheres can induce a significant anisotropy in the scattering pattern. We here have shown that even small variations in the nanoparticle geometry that are difficult to resolve with SEM can lead to significant effects in the plasmonic coupling, therefore affecting the scattering spectra of the assembled nanostructures

Comparison between early and delayed facial nerve decompression in traumatic facial nerve paralysis - A retrospective study

ABSTRACT Purpose To study the intraoperative findings in case of early and delayed decompression of facial nerve paralysis and compare their results. Methods Retrospective data analysis of 23 cases of longitudinal temporal bone fracture with House-Brackmann grade V and VI facial nerve paralysis. All cases were thoroughly evaluated and underwent facial nerve decompression through the transmastoid approach. All cases were under regular follow-up till the date of manuscript submission. Results Clinical improvement of the facial nerve function was observed for early vs. delayed facial nerve decompression. In the early decompression group, facial nerve function improved to grade II in eight cases (80%) and grade III in two cases (20%), whereas in the delayed decompression group it improved to grade II in one case (7.70%), grade III in four cases (30.76%), grade IV in seven cases (53.84%), and grade V in one case (7.70%). Conclusions Early decompression of facial nerve provides better results than delayed decompression because it enables early expansion of the nerve

Effect of Gradient Alloying on Photoluminescence Blinking of Single CdS_<i>x</i>Se_1–<i>x</i> Nanocrystals

Alloyed CdS_<i>x</i>Se_1–<i>x</i> semiconductor nanocrystals (NCs) were obtained from a one-pot synthesis at reduced temperature with moderate quantum yield. Comprehensive structural characterizations of the CdSSe NCs reveal that the NCs have gradient alloyed structure, with Cd evenly distributed over the entire NC, Se rich in the center, and S rich in the outer region. This is due to the difference in the nucleation kinetics of S and Se precursors. Optical studies at the single NC level show that the NCs have reduced photoluminescence blinking, increased “on” time fraction, and good photostability, in comparison with CdSe NCs. The incorporation of sulfur composition in the alloy NCs improves surface passivation and in turn protects the NCs from (photo)­oxidation. The gradual change in the NC composition from center to outer regions creates a smooth “interface”, compared to core/shell NCs. These factors lead to reduced nonradiative rates in the NCs, improving their emitting properties

Blue-Shifted Narrow Localized Surface Plasmon Resonance from Dipole Coupling in Gold Nanoparticle Random Arrays

In this work, we develop a simple method to produce highly uniform localized surface plasmon resonance (LSPR) substrates based on self-assembly of colloidal gold nanoparticles onto pretreated glass substrates. The LSPR wavelength of the gold nanoparticle arrays is blue-shifted from that of the gold nanoparticles in solution and the single gold nanoparticles on glass substrate. The LSPR width is narrower than that of the single gold nanoparticles. The blue-shifted LSPR is due to the long-range dipole coupling in the gold nanoparticle random arrays indicated from simulations using the T-matrix method. In addition to the popularly used LSPR wavelength dependence on the dielectric environment, we have found that the LSPR width of the gold nanoparticle random arrays is also sensitive to the change in the dielectric environment. The LSPR substrates are reproducible, uniform, and robust with potential applications in LSPR sensing and imaging