Photoactivated localization microscopy (PALM): an optical technique for achieving ~10-nm resolution

The organization of proteins on the scale of a few tens of nanometers, such as in the postsynaptic density and the synaptic vesicles, is a key determinant of their function. However, spatial features on such a fine scale are beyond the resolving power of conventional, diffraction-limited fluorescence light microscopy. In response, several imaging modalities have recently emerged that can surpass the diffraction limit on optically benign samples in which aberration and light scattering are negligible. Although each of these techniques has its own advantages and limitations, photoactivated localization microscopy (PALM) provides the highest shown resolution in biological samples, is the most efficient in utilizing signal photons, and allows for the assessment of individual molecules. This article discusses the basic principles of PALM microscopy, its implementation, and the potential applications in neuroscience.