Here's why:
* Diffraction Limit: Light microscopes are limited by the diffraction of light. This means that light waves bend around small objects, blurring the image. The diffraction limit determines the minimum distance between two objects that can be distinguished as separate entities. This limit is approximately half the wavelength of light used.
* Visible Light: Visible light has wavelengths ranging from 400 to 700 nm.
* Super-Resolution Microscopy: Techniques like stimulated emission depletion (STED) microscopy and single-molecule localization microscopy (SMLM) have pushed the resolution limit of light microscopy beyond the diffraction limit, allowing visualization of structures down to ~20 nm. However, these techniques are more specialized and not as widely used as traditional light microscopy.
Therefore, while 200 nm is the approximate limit for standard light microscopy, super-resolution techniques can achieve much higher resolution, enabling the visualization of even smaller structures.
