Why an optical microscope is not used to measure the size of a molecule?

Size of molecule ranges from ${{10}^{-8}}$ m to ${{10}^{-10}}$ m. An optical microscope uses visible light of average wavelength 6000 $A\overset{0}{\mathop{{}}},$, i.e., 6000 x ${{10}^{-10}}$ m to measure the sizes. Since size of molecule is smaller than the wavelength of light used, so optical microscope cannot resolve a molecule