Synthesis, Surface Modification, and Characterization of Metal Oxide Nanoparticles : Nanoprobes for Signal Enhancement in Biomedical Imaging

In this thesis we investigate crystalline metal oxide nanoparticles of our own design to obtain nanoprobes for signal enhancement and bioimaging purposes. We report fabrication, surface modification and characterization of nanoparticles based on zinc (Zn), and rare earths (i.e. gadolinium (Gd) and europium (Eu)) singly and in combination. Our ZnO nanoparticles show high potential as fluorescent probes and Gd2O3 nanoparticles are promising as nanoprobes for MR signal enhancement. A combined Zn, Gd material is investigated as a potential dual probe. Interestingly, this nanoprobe shows, compared to the pure oxides, both increased fluorescent quantum yield and do induce improved relaxivity and by that enhanced MR signal. Nanoparticles composed of Eu doped Gd2O3 are also investigated in terms of their ability to interact with silicon surfaces. The presence of nanoparticles shows a catalytic effect on the annealing procedure of SiOx. Surface modification of Gd and Zn based nanoparticles is performed, in a first step to improve stabilization of the nanoparticle core. Both carboxylic acids (paper I) and a thiol terminated silane (paper II and III) are used for this purpose. In a second step, a polyethylene glycol (PEG) is used for surface modification, to increase the biocompatibility of the nanoparticles. The Mal PEG NHS is chemically linked to thiol terminated silane groups via a maleimide coupling (Paper II). The presence of free NHS functional groups is intended to enable further linking of specific molecules for targeting purposes. The fluorescent dye rhodamine was, as a proof of concept, linked via the NHS functional group to the PEGylated Gd2O3 nanoparticles (Paper II). In Paper III, an alternative linking strategy is investigated, using iodized PEG2-Biotin for coupling via the iodide unit to the thiol terminated silane on ZnO nanoparticles. The resulting surface modified nanoparticles are investigated by means of coordination chemistry and coupling efficiency using X-ray photoelectron spectroscopy, near edge X-ray absorption fine structure  spectroscopy and infrared spectroscopy

Step by step rare-earth catalyzed SiOx annealing and simultaneous formation of Europium- silicide by low coverage of Eu doped Gd2O3 nanoparticles

We report the formation of silicide by annealing of a SiOx surface, with low coverage of Eu doped Gd2O3 nanoparticles. The annealing temperature required for removal of native oxide from the Si substrate decreases with close to 200 °C in presence of the nanoparticles. X-ray photoemission electron microscopy, low-energy electron microscopy and mirror electron microscopy are used to monitor the silicide formation and SiOx removal. Fragmentation of the nanoparticles is observed, and the SiOx layer is gradually removed. Eu migrates to clean Si areas during the annealing process, while Gd is found in areas where oxide is still present. This annealing process is clearly facilitated in the presence of rare-earth based nanoparticles, where nanoparticles are suggested to function as reaction sites to catalyze the oxygen removal and simultaneously form Eu based silicide. Reduction of the annealing temperature of SiOx substrates is also observed in presence of pure Eu3+ and Gd3+ ions. Simultaneous oxygen removal and EuSi formation enable this new rare-earth catalyzed annealing and silicide formation to find applications both within optoelectronics and processing microelectronic industry

The Influence of Sonication Processing Conditions on Electrical and Mechanical Properties of Single and Hybrid Epoxy Nanocomposites Filled with Carbon Nanoparticles

Graphene nanoplatelets (GNP) and carbon nanotubes (CNT) are used to enhance electrical and mechanical properties of epoxy-based nanocomposites. Despite the evidence of synergetic effects in the hybrid GNP-CNT-epoxy system, there is still a lack of studies that focus on the influence of different dispersion methods on the final properties of these ternary systems. In the present work, direct and indirect ultrasonication methods were used to prepare single- and hybrid-filled GNP-CNT-epoxy nanocomposites, varying the amplitude and time of sonication in order to investigate their effect on electrical and thermomechanical properties. Impedance spectroscopy was combined with rheology and electron microscopy to show that high-power direct sonication tends to degrade electrical conductivity in GNP-CNT-epoxy nanocomposites due to damage caused in the nanoparticles. CNT-filled samples were mostly benefitted by low-power direct sonication, achieving an electrical conductivity of 1.3 × 10−3 S·m−1 at 0.25 wt.% loading, while indirect sonication was not able to properly disperse the CNTs and led to a conductivity of 1.6 ± 1.3 × 10−5. Conversely, specimens filled with 2.5 wt. % of GNP and processed by indirect sonication displayed an electrical conductivity that is up to 4 orders of magnitude higher than when processed by direct sonication, achieving 5.6 × 10−7 S·m−1. The introduction of GNP flakes improved the dispersion state and conductivity in hybrid specimens processed by indirect sonication, but at the same time impaired these properties for high-power direct sonication. It is argued that this contradictory effect is caused by a selective localization of shorter CNTs onto GNPs due to strong π-π interactions when direct sonication is used. Dynamic mechanical analysis showed that the addition of nanofillers improved epoxy’s storage modulus by up to 84%, but this property is mostly insensitive to the different processing parameters. Decrease in crosslinking degree and presence of residual solvent confirmed by Fourier-transform infrared spectroscopy, however, diminished the glass transition temperature of the nanocomposites by up to 40% when compared to the neat resin due to plasticization effects

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A simple polyol-free synthesis route to Gd2O

A simple polyol-free synthesis route to Gd2O3 nanoparticles for MRI applications: an experimental and theoretical study

Chelated gadolinium ions, e. g., GdDTPA, are today used clinically as contrast agents for magnetic resonance imaging (MRI). An attractive alternative contrast agent is composed of gadolinium oxide nanoparticles as they have shown to provide enhanced contrast and, in principle, more straightforward molecular capping possibilities. In this study, we report a new, simple, and polyol-free way of synthesizing 4-5-nm-sized Gd2O3 nanoparticles at room temperature, with high stability and water solubility. The nanoparticles induce high-proton relaxivity compared to Gd-DTPA showing r(1) and r(2) values almost as high as those for free Gd3+ ions in water. The Gd2O3 nanoparticles are capped with acetate and carbonate groups, as shown with infrared spectroscopy, near-edge X-ray absorption spectroscopy, X-ray photoelectron spectroscopy and combined thermogravimetric and mass spectroscopy analysis. Interpretation of infrared spectroscopy data is corroborated by extensive quantum chemical calculations. This nanomaterial is easily prepared and has promising properties to function as a core in a future contrast agent for MRI.Funding Agencies|VINNOVA|2008-03011|Centre in Nanoscience and Technology at LiTH (CeNano)||Swedish research council|621-2010-5014|SERC (Swedish e-Science Research Center)||</p

Fabrication of multi-layer CoSnO3@carbon-caged NiCo2O4 nanobox for enhanced lithium storage performance

Mixed transition metal oxides (MTMOs) are deemed as promising anode materials for lithium-ion batteries (LIBs) because of the high theoretical capacity and low cost. However, the low electrical conductivity, agglomeration effects, and huge volume variation during discharging/charging still seriously restrict the actual applications of MTMOs as anode materials. Herein, a novel core-shell structure of CoSnO3@carbon-caged NiCo2O4 nanobox (CNC) is rationally designed. It starts from the preparation of CoSnO3@ZIF-67 core-shell nanocubes, followed by chemical etching/anion exchange, dopamine coating and carbonization at high temperature in sequence. It is shown that the CNC achieves high activities from the applied MTMOs components, excellent relief of volume variation from the unique double hollow structure, improved conductivity and inhabited aggregations from the uniform-coated outmost carbon shell, and effective ion/electron transfer rates from the synergetic effects. As a result, the CNC exhibits a discharge capacity of 1548 mA h g(-1) at the first cycle and a retention capacity of 992 mA h g(-1) after 100 cycles at 0.1 A g(-1). In addition, it exhibits a high reversible capacity of about 670 mA h g(-1) after 500 cycles at a current density of 1 A g(-1). The improved Li+ storage performances of CNC demonstrates that such rational design of double hollow structure could be a novel strategy to apply MTMOs as anode materials of LIBs.Funding Agencies|National Natural Science Foundation of ChinaNational Natural Science Foundation of China (NSFC) [21601120]; Science and Technology Commission of Shanghai MunicipalityScience &amp; Technology Commission of Shanghai Municipality (STCSM) [17ZR1410500, 19ZR1418100]; Swedish Government strategic faculty grant in material science (SFO, MATLIU) in Advanced Functional Materials (AFM) (VR) [5.1-2015-5959]; Swedish Foundation for Strategic Research (SSF)Swedish Foundation for Strategic Research [SM17-0026]</p