Climbing the steps of viral atomic force microscopy: visualization of Dengue virus particles.

In recent years, the application of atomic force microscopy (AFM) to biological systems has highlighted the potential of this technology. AFM provides insights into studies of biological structures and interactions and can also identify and characterize a large panel of pathogens, including viruses. The Flaviviridae family contains a number of viruses that are important human and animal pathogens. Among them, Dengue virus causes epidemics with fatal outcomes mainly in the tropics. In this study, Dengue virus is visualized for the first time using the in air AFM technique. Images were obtained from a potassium-tartrate gradient-purified virus. This study enhances the application of AFM as a novel tool for the visualization and characterization of virus particles. Because flavivirus members are closely related, studies of the morphologic structure of the Dengue virus can reveal strategies that may be useful to identify and study other important viruses in the family, including the West Nile virus.

Use of atomic force microscopy as a diagnostic tool to identify orthopoxvirus.

Atomic force microscopy (AFM) is a versatile technique that permits the imaging of surfaces and generates topographical images from a variety of materials. Due to the fact that AFM requires minimum sample manipulation, it is a valuable tool for studying biological materials such as cells, DNA, bacteria and viruses. The aim of the present study was to standardize the AFM technique as a diagnostic tool for detection of naturally occurring orthopoxviruses. The samples analyzed were collected during natural outbreaks of Vaccinia virus (VACV) in dairy cattle in Brazil. These viruses are zoonotic infections; and therefore safe manipulation of all samples is required. The AFM technique would provide a more secure way to diagnose infection. By using the "in air" AFM technique after purification and inactivation process, relatively crude preparations of viruses were visualized rapidly. Details for efficient sample preparation and AFM imaging are described. The AFM technique provides a rapid and biosecure tool for the diagnosis of emerging orthopoxviruses and has potential as a tool for screening bioterrorism samples.

Structural and optical characterization of strained free-standing InP nanowires.

The structural and optical properties of high-quality crystalline strained InP nanowires are reported in this article. The nanowires were produced by the vapor-liquid-solid growth method in a chemical-beam epitaxy reactor, using 20 nm gold nanoparticles as catalysts. Polarization-resolved photoluminescence experiments were carried out to study the optical properties of the InP nanowires. These experiments revealed a large blue shift of 74 meV of the first electron-to-heavy hole optical transition in the nanowires, which cannot be solely explained by quantum size effects. The blue shift is mainly attributed to the presence of biaxial compressive strain in the inward radial direction of the InP nanowires. High-resolution transmission electron microscopy Electron and selected area electron diffraction experiments show that the nanowires have high crystal quality and grow along a [001] axes. These experiments also confirmed the presence of 1.8% compressive radial strain and 2% tensile longitudinal strain in the nanowires. A simple theoretical model including both quantum confinement and strain effects consistently describes the actual energy position of the InP nanowires optical emission.