ABSTRACT
Understanding the structural organization of cells is essential for learning how they function. Animal cells are not only tiny, but they are also colorless and translucent. The discovery of their main internal features, therefore, depended on the development, in the late nineteenth century, of a variety of stains that provided sufficient contrast to make those features visible. For well over 100 years, all microscopes were constrained by a fundamental limitation: that a given type of radiation cannot be used to probe structural details much smaller than its own wavelength. Because of its wave nature, light does not follow the idealized straight ray paths that geometrical optics predicts. Although no amount of refinement of the lenses can overcome the diffraction limit imposed by the wavelike nature of light, other ways of cleverly bypassing this limit have emerged, creating so-called super-resolution imaging techniques that can even detect the position of single molecules.
