Optical imaging of nanoscale cellular structures.

Visualization of subcellular structures and their temporal evolution is of utmost importance to understand a vast range of biological processes. Optical microscopy is the method of choice for imaging live cells and tissues; it is minimally invasive, so processes can be observed over extended periods of time without generating artifacts due to intense light irradiation. The use of fluorescence microscopy is advantageous because biomolecules or supramolecular structures of interest can be labeled specifically with fluorophores, so the images reveal information on processes involving only the labeled molecules. The key restriction of optical microscopy is its moderate resolution, which is limited to about half the wavelength of light (∼200 nm) due to fundamental physical laws governing wave optics. Consequently, molecular processes taking place at spatial scales between 1 and 100 nm cannot be studied by regular optical microscopy. In recent years, however, a variety of super-resolution fluorescence microscopy techniques have been developed that circumvent the resolution limitation. Here, we present a brief overview of these techniques and their application to cellular biophysics.