In theory, yes. To achieve this resolution would require an objective with a high numerical aperature (NA ~1.4), and visualization with lower wavelengths of light -- for example a fluorescent tag emitting in the low 400 nm range. Take a look at a site called Microscopy U for more details
http://www.microscopyu.com/
Newer generation microscopes can exceed this resolution limit using (a lot of) computing power to deconvolute and reconstruct images based on variations in light coming from the sample.
Here is a detailed article about the limit of resolution in optical microscopy, and the various methods used to obtain resolution below the diffraction limit:
http://zeiss-campus.magnet.fsu.edu/articles/superresolution/introduction.html
Yes, ~200nm is generally the diffraction limit of light microscopy as proposed by Abbe. However, in addition to Marc's response there are super-resolution microscopy methods which are able to bypass this traditional limit physically, separate to deconvolution.
For instance, STED microscopy functions by using a donut-shaped STED laser beam surrounding the excitation laser beam to redshift the fluorophores around the excited area. Additionally you can further resolve individual fluorophore molecules by their differing lifetimes with a pulsed STED beam in gated STED.
You can read up more about STED and other super-resolution fluorescence techniques in the attached review.
Article The Principles of Super-Resolution Fluorescence Microscopy (Review)
It is true that the best light microscope has a resolution of 0.2 micrometers which is equivalent to 200 nanometers, The resolution of a microscope takes into consideration it,s wavelength of light , refractive index, and angular aperture.
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