Electromagnetic surface waves propagate along the interface between a thin metallic film and a dielectric medium and then are highly sensitive to changes in the properties of the involved media. In this paper, we will give a brief outline of the principles of the optical technique based upon Attenuated Total Reflexion (ATR). Tin nanoparticles, mean sizes ranging down to 1 nm, are embedded in a dielectric medium deposited onto the metallic film which guides the surface waves. We present some results showing that melting and freezing of such small particles can be studied with ATR. The influence of the distance between the particles and the interface will be discussed.