Electron microscopy of nanoparticle superlattice formation at a solid-liquid interface in nonpolar liquids.

Nanoparticle superlattice films form at the solid-liquid interface and are important for mesoscale materials, but are notoriously difficult to analyze before they are fully dried. Here, the early stages of nanoparticle assembly were studied at solid-liquid interfaces using liquid-phase electron microscopy. Oleylamine-stabilized gold nanoparticles spontaneously formed thin layers on a silicon nitride (SiN) membrane window of the liquid enclosure. Dense packings of hexagonal symmetry were obtained for the first monolayer independent of the nonpolar solvent type. The second layer, however, exhibited geometries ranging from dense packing in a hexagonal honeycomb structure to quasi-crystalline particle arrangements depending on the dielectric constant of the liquid. The complex structures formed by the weaker interactions in the second particle layer were preserved, while the surface remained immersed in liquid. Fine-tuning the properties of the involved materials can thus be used to control the three-dimensional geometry of a superlattice including quasi-crystals.

Comparison of plaque reduction neutralisation test (PRNT) and measles virus-specific IgG ELISA for assessing immunogenicity of measles vaccination.

BACKGROUND: Plaque reduction neutralisation test (PRNT) is a gold standard assay for measles antibodies. PRNT, however, is time-consuming and more difficult to standardise than ELISA. METHODS: PRNT results were obtained on pre- and post-vaccination sera from 501 measles-vaccinated infants. From this cohort a sub-set of 210 infants were selected for testing by ELISA, which was performed either manually or by an automated processor. Results were corrected for sampling proportion before comparing the assays. RESULTS: Seroconversion was detected by PRNT in 454 infants of whom 324 were estimated to have seroconverted by manual ELISA and 191 by automated ELISA It is recommended that ELISA negative post-vaccination samples are re-tested by PRNT to detect all seroconversions.

Measles immunity testing: comparison of two measles IgG ELISAs with plaque reduction neutralisation assay.

Two commercial IgG ELISAs, one based on recombinant nucleocapsid antigen and one based on cell culture grown native virus antigens, were evaluated for measles immunity testing by comparison with plaque reduction neutralisation test (PRNT). Qualitative results of the two ELISAs showed 92% agreement with those of PRNT. The sensitivity of the two ELISAs was 89.6%. False negative ELISA results were obtained in 10% of sera, mainly sera containing low levels of neutralising antibody. The specificity of both ELISAs was 100%. Measles IgG ELISAs perform adequately for immunity testing, correctly identifying seronegative individuals for vaccination.