German physicist Gustav Mie played a role in nanotechnology with his theory of light scattering by particles. His theory shows that light scatters from particles more efficiently at short wavelengths than at long wavelengths.
For example, we see the sky as being blue because the molecules in the air (which are extremely small particles) scatter light from the sun more efficiently for blue light than for yellow or red, as blue light has the shorter wavelength. When the sun sets, the sunlight travels through the atmosphere over a longer distance than when it's overhead. The most important scattering in this case arises from dust particles. These particles still scatter light more effectively for blue colors, so the light that is not scattered is a mixture of red and yellow. This produces the characteristic red color of the setting sun.
Mie theory helped scientists to realize that the size of particles determines the colors that we see. Mie went on to develop a way to calculate the size of particles by determining the light scatter. For nanoparticles and larger particles, this theory requires a huge number of calculations, so it was rarely used until about 20 years ago when supercomputers became available. Now, Mie theory (as well as others developed more recently) helps researchers predict and determine the size of nanoparticles.