Single particle analysis

Single particle analysis is a group of related computerized image processing techniques used to analyze images from transmission electron microscopy (TEM).^[1] These methods were developed to improve and extend the information obtainable from TEM images of particulate samples, typically proteins or other large biological entities such as viruses. Individual images of stained or unstained particles are very noisy, making interpretation difficult. Combining several digitized images of similar particles together gives an image with stronger and more easily interpretable features. An extension of this technique uses single particle methods to build up a three-dimensional reconstruction of the particle. Using cryo-electron microscopy it has become possible to generate reconstructions with sub-nanometer resolution and near-atomic resolution^[2][3] first in the case of highly symmetric viruses, and now in smaller, asymmetric proteins as well.^[4] Single particle analysis can also be performed by inductively coupled plasma mass spectrometry (ICP-MS).