Shape controlled iron oxide nanoparticles: inducing branching and controlling particle crystallinity

Anisotropic nanoparticles (NPs) have garnered a great deal of attention for their applications in catalysis, magnetism and biomedicine. However, synthetic strategies to grow such NPs are still limited as their growth mechanisms are poorly understood. This work presents the synthesis of iron oxide nanoparticles (IONPs) based on the decomposition of iron(III) acetylacetonate in organic solvents to form anisotropic IONPs that are branched or multiply branched. We fully explore their growth parameters to understand the effect of varying amounts of oleylamine (OAm), as well as a nitrogen purge on particle morphology. We show here the synthetic relationship between a wide range of sizes and shapes of IONPs that are both isotropic and anisotropic. Of all the parameters, the amount of oleylamine in the reaction is the key to tune the particle size while the effect of a nitrogen gas purge during synthesis was shown to be crucial for the formation of the branched and multiply branched NPs. Two multiply branched NP systems with only a small difference in the synthetic conditions were shown to have radically different magnetic properties, such as heating in an alternating magnetic field. This was attributed to the defects found in the structure of one and not in the other. By following their development during growth, crystal defects were observed in both systems during the early stages of the reaction. However, for the multiply branched structure that became single crystalline, the aggregation of the nuclei occurred earlier in the reaction, allowing more time for growth and crystallite rearrangement to occur. These results have wide ranging implications for controlling the properties of anisotropic nanomaterials with similar structures, including their magnetic behavior

Methods to discriminate primary from secondary dengue during acute symptomatic infection

BACKGROUND: Dengue virus infection results in a broad spectrum of clinical outcomes, ranging from asymptomatic infection through to severe dengue. Although prior infection with another viral serotype, i.e. secondary dengue, is known to be an important factor influencing disease severity, current methods to determine primary versus secondary immune status during the acute illness do not consider the rapidly evolving immune response, and their accuracy has rarely been evaluated against an independent gold standard. METHODS: Two hundred and ninety-three confirmed dengue patients were classified as experiencing primary, secondary or indeterminate infections using plaque reduction neutralisation tests performed 6 months after resolution of the acute illness. We developed and validated regression models to differentiate primary from secondary dengue on multiple acute illness days, using Panbio Indirect IgG and in-house capture IgG and IgM ELISA measurements performed on over 1000 serial samples obtained during acute illness. RESULTS: Cut-offs derived for the various parameters demonstrated progressive change (positively or negatively) by day of illness. Using these time varying cut-offs it was possible to determine whether an infection was primary or secondary on single specimens, with acceptable performance. The model using Panbio Indirect IgG responses and including an interaction with illness day showed the best performance throughout, although with some decline in performance later in infection. Models based on in-house capture IgG levels, and the IgM/IgG ratio, also performed well, though conversely performance improved later in infection. CONCLUSIONS: For all assays, the best fitting models estimated a different cut-off value for different days of illness, confirming how rapidly the immune response changes during acute dengue. The optimal choice of assay will vary depending on circumstance. Although the Panbio Indirect IgG model performs best early on, the IgM/IgG capture ratio may be preferred later in the illness course