One of the most-important tools in modern science is the analysis of electromagnetic properties by spectroscopy. The various types of spectroscopy can be classified by the underlying type of interactions between energy and the material. In this paper we demonstrate a class of spectroscopy based on Casimir interactions between a solid investigated object and a reference surface embedded in an environmental liquid medium. Our main example is based on the measurement of Hamaker constants on change of the concentration of an intervening two-component liquid, where we demonstrate a possible reconstruction algorithm to estimate the frequency-dependent dielectric function of the particle investigated.