Individual virus weighed precisely

The masses of individual virus particles and the mass variability of each population of a virus can yield important information about the nature and structure of these genetically diverse biological entities. A group led by Huan-Cheng Chang of Academia Sinica, Taipei, Taiwan, has now developed a method for measuring the mass of a single whole virus to within ±1% precision, compared with typically ±15% precision for previous methods (Angew. Chem. Int. Ed. 2006, 45, 8131). The method uses a "gentle" ionization technique, known as laser-induced acoustic desorption, to generate intact viral ions. The ions are collected in a cylindrical ion trap equipped with transparent electrodes, and they oscillate in the electric field with a frequency that depends on their mass and charge. The frequency is determined by analysis of light scattered from individual particles when laser light is beamed into the trap. The team used the method to measure the masses of three types of viruses with diameters between 80 and 300 nm and masses in the range of 10⁸-10⁹ daltons.