Two dimensional dipolar coupling in monolayers of silver and gold nanoparticles on a dielectric substrate

The dimensionality of assembled nanoparticles plays an important role in their optical and magnetic properties, via dipolar effects and the interaction with their environment. In this work we develop a methodology for distinguishing between two (2D) and three (3D) dimensional collective interactions on the surface plasmon resonance of assembled metal nanoparticles. Towards that goal, we elaborate different sets of Au and Ag nanoparticles as suspensions, random 3D arrangements and well organized 2D arrays. Then we model their scattering cross-section using effective field methods in dimension n, including interparticle as well as particle-substrate dipolar interactions. For this modelling, two effective field medium approaches are employed, taking into account the filling factors of the assemblies. Our results are important for realizing photonic amplifier devices

Difficult tracheal intubation in neonates and infants. NEonate and Children audiT of Anaesthesia pRactice IN Europe (NECTARINE): a prospective European multicentre observational study

Background: Neonates and infants are susceptible to hypoxaemia in the perioperative period. The aim of this study was to analyse interventions related to anaesthesia tracheal intubations in this European cohort and identify their clinical consequences. Methods: We performed a secondary analysis of tracheal intubations of the European multicentre observational trial (NEonate and Children audiT of Anaesthesia pRactice IN Europe [NECTARINE]) in neonates and small infants with difficult tracheal intubation. The primary endpoint was the incidence of difficult intubation and the related complications. The secondary endpoints were the risk factors for severe hypoxaemia attributed to difficult airway management, and 30 and 90 day outcomes. Results: Tracheal intubation was planned in 4683 procedures. Difficult tracheal intubation, defined as two failed attempts of direct laryngoscopy, occurred in 266 children (271 procedures) with an incidence (95% confidence interval [CI]) of 5.8% (95% CI, 5.1e6.5). Bradycardia occurred in 8% of the cases with difficult intubation, whereas a significant decrease in oxygen saturation (SpO2<90% for 60 s) was reported in 40%. No associated risk factors could be identified among comorbidities, surgical, or anaesthesia management. Using propensity scoring to adjust for confounders, difficult anaesthesia tracheal intubation did not lead to an increase in 30 and 90 day morbidity or mortality. Conclusions: The results of the present study demonstrate a high incidence of difficult tracheal intubation in children less than 60 weeks post-conceptual age commonly resulting in severe hypoxaemia. Reassuringly, the morbidity and mortality at 30 and 90 days was not increased by the occurrence of a difficult intubation event. Clinical trial registration: NCT02350348

Variation in Structure and Process of Care in Traumatic Brain Injury: Provider Profiles of European Neurotrauma Centers Participating in the CENTER-TBI Study.

INTRODUCTION: The strength of evidence underpinning care and treatment recommendations in traumatic brain injury (TBI) is low. Comparative effectiveness research (CER) has been proposed as a framework to provide evidence for optimal care for TBI patients. The first step in CER is to map the existing variation. The aim of current study is to quantify variation in general structural and process characteristics among centers participating in the Collaborative European NeuroTrauma Effectiveness Research in Traumatic Brain Injury (CENTER-TBI) study. METHODS: We designed a set of 11 provider profiling questionnaires with 321 questions about various aspects of TBI care, chosen based on literature and expert opinion. After pilot testing, questionnaires were disseminated to 71 centers from 20 countries participating in the CENTER-TBI study. Reliability of questionnaires was estimated by calculating a concordance rate among 5% duplicate questions. RESULTS: All 71 centers completed the questionnaires. Median concordance rate among duplicate questions was 0.85. The majority of centers were academic hospitals (n = 65, 92%), designated as a level I trauma center (n = 48, 68%) and situated in an urban location (n = 70, 99%). The availability of facilities for neuro-trauma care varied across centers; e.g. 40 (57%) had a dedicated neuro-intensive care unit (ICU), 36 (51%) had an in-hospital rehabilitation unit and the organization of the ICU was closed in 64% (n = 45) of the centers. In addition, we found wide variation in processes of care, such as the ICU admission policy and intracranial pressure monitoring policy among centers. CONCLUSION: Even among high-volume, specialized neurotrauma centers there is substantial variation in structures and processes of TBI care. This variation provides an opportunity to study effectiveness of specific aspects of TBI care and to identify best practices with CER approaches

Films of Tunable ZnO Nanostructures Prepared by a Surfactant-Mediated Soft Synthesis Route

Films of ZnO nanostructures were prepared by a soft chemical synthesis route from ZnO crystal seeds in aqueous medium, in the presence of alkylsulfates of different chain length acting as structure-directing agents. Films of arrayed single crystal ZnO nanorods were formed with short alkyl sulfates, from C6 to C8 alkylene chains, while hybrid lamellar ZnO with a platelike morphology were obtained with C10 to C18 alkyl sulfates. In the case of the short alkyl sulfates, due to the interaction between the sulfate groups and the Zn2+ planes of the ZnO structure, the growth along the c axis is partially inhibited and smaller aspect ratios of the nanorods are obtained than in alkylsulfate-free conditions. In the case of the hybrid lamellar ZnO structures which consist in ZnO layers intercalated with alkylsulfate bilayers, the structural characteristics depend on the alkylene chain length. Basal spacings increase linearly with the chain length, while the plate size decreases dramatically when the chain length exceeds C14. The different characteristics of these ZnO nanostructured films allow modifying their optical properties

Magnetic Properties of Mono- and Multilayer Assemblies of Iron Oxide Nanoparticles Promoted by SAMs

Owing to the wide scope of applications of magnetic nanoparticle assembling, the aim of this study is to evaluate the influence of nanoparticle aggregates on the magnetic properties of 2D assemblies. Magnetic iron oxide nanoparticles (NPs) have been synthesized by the coprecipitation (NPcop) and thermal decomposition (NPdec@OA) methods, and were assembled on self-assembled monolayers of organic molecules decorated by a phosphonic acid terminal group at their surface (SAM-PO3H2). The nanostructure and magnetic properties of assemblies depend directly on the aggregation of NP suspensions. NPcop, result in an unstable suspension and were assembled into a non-homogeneous monolayer of aggregates. The post-functionalization of NPcop with oleic acid after synthesis (NPcop@OA) favors a better stability of the suspension and enhances the nanostructure of the assembly, although smaller NP aggregates remain. In contrast, NPdec@OA which are functionalized in situ by oleic acid during the synthesis step were assembled as individual nanomagnets and result in a dense monolayer. Multi layer assemblies were also prepared from NPcop@OA and NPdec@OA by performing the alternative deposition of these NPs with (1,4-phenylene)bisphosphonic acid. The nanostructure of assemblies has been studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The magnetic properties of monolayer and multilayer assemblies have been studied by using a SQUID magnetometer. While assemblies of individual NPs enhance dipolar interactions in-plane as a result of shape anisotropy, assemblies of NP aggregates favor stronger dipolar interactions with random orientation. The magnetic properties of monolayer and multilayer assemblies have also been compared. The dimensionality (2D vs 3D) has a strong effect on the dipolar interactions when individual NPs are considered in contrast to aggregated nanoparticles

Size dependent dipolar interactions in iron oxide nanoparticle monolayer and multilayer Langmuir-Blodgett films

The dipolar interactions in monolayer and multilayer assemblies of iron oxide nanoparticles have been investigated as a function of the nanoparticle size. The magnetic properties of iron oxide nanocrystals of various sizes have been measured for particles as powders and assembled in mono-and multilayers by the Langmuir-Blodgett technique, and compared to the behavior of non-interacting nanoparticles. It is shown that increasing dipolar interactions lead to higher blocking temperatures and to deviation from the Neel-Brown law. Dipolar interactions are found to be stronger for particles assembled in thin films compared to powdered samples. The effect of interactions increases strongly with the nanoparticle size in agreement with simulations, leading to an unusual behaviour for the larger particles assembled in monolayer, which could be a signature of a superferromagnetic state.Financial support was provided by the Agence Nationale pour la Recherche (ANR MAGARRAYS) and the Direction Générale de l’Armement (DGA). The authors thank Cedric Leuvrey for SEM pictures, Dris Ihiawakrim and Corinne Ulhaq for TEM pictures, Christophe Lefevre for XRD refinement, and Alain Derory for technical support with SQUID measurements

Size-dependent properties of magnetic iron oxide nanocrystals

The fine control of iron oxide nanocrystal sizes within the nanometre scale (diameters range from 2.5 to 14 nm) allows us to investigate accurately the size-dependence of their structural and magnetic properties. A study of the growth conditions of these nanocrystals obtained by thermal decomposition of an iron oleate precursor in high-boiling point solvents has been carried out. Both the type of solvent used and the ligand/precursor ratio have been systematically varied, and were found to be the key parameters to control the growth process. The lattice parameters of all the nanocrystals deduced from X-ray diffraction measurements are consistent with a structure of the type Fe(3-x)O(4), i.e. intermediate between magnetite and maghemite, which evolves toward the maghemite structure for the smallest sizes (x = 1/3). The evolution of the magnetic behavior with nanoparticle sizes emphasizes clearly the influence of the surface, especially on the saturation magnetization M(s) and the magneto-crystalline anisotropy K. Dipolar interactions and thermal dependence have been also taken into account in the study on the nanoscale size-effect of magnetic properties

Co-tunneling Enhancement of the Electrical Response of Nanoparticle Networks

A co-tunneling charge-transfer process dominates the electrical properties of a nanometer-sized slice in a nanoparticle network, which results in universal scaling of the conductance with temperature and bias voltage, as well as enhanced spintronics properties. By designing two large (10 mu m) electrodes with short (60 nm) separation, access is obtained to transport dominated by charge transfer involving nanoslices made of three nanoparticles only. Magnetic iron oxide nanoparticle networks exhibit a magnetoresistance ratio that is not reachable by tunneling or hopping processes, thereby illustrating how such a size-matched planar device with dominant co-tunneling charge-transfer process is optimal for realizing multifunctional devices with enhanced change of conductance under external stimulus

Design, synthesis, characterization and properties of magnetic nanoparticle-nanocarbon hybrids

Carbon nanostructured materials such as carbon nanotubes and graphene oxide are attracting much attention due to their outstanding chemical and physical properties. Metal nanoparticle-decoration can provide additional functionalities to these nanocarbons. Many chemical methods are being used for the synthesis of these metal nanoparticle-functionalized nanocarbon hybrids. On the other hand, the outstanding properties of spinelle iron oxide magnetic (MAG) nanoparticles have been efficiently used for a variety of applications such as manipulation of biomolecules and cells, cancer hyperthermia, and medical devices. Therefore, MAG nanoparticle decoration of carbon nanotubes and graphene oxide can provide promising nanohybrid materials for nanobiotechnological applications. In this work, we present a straightforward chemical route for MAG nanopartide decoration of nanocarbon supports including carbon nanotubes and graphene oxide using in situ high-temperature decomposition method. This chemical methodology allows precisely controlling the MAG nanoparticle content, the MAG nanopartide size leading to a uniform coating on the different carbon supports. The properties of these new hybrids have been thoroughly evaluated. Our results show that the MAG nanoparticle decoration process strongly affects the structural and magnetic characteristics of the hybrids. The combination of MAG nanopartide and nanocarbon materials will open the door to their use in different domains including nanocomposites, wastewater treatment, sensors, biomaterials, and cancer therapy. (C) 2015 Elsevier Ltd. All rights reserved