The present invention relates to a method and an apparatus for a fast thermo-optical characterisation of particles. In particular, the present invention relates to a method and a device to measure the stability of (bio)molecules, the interaction of molecules, in particular biomolecules, with, e.g. further (bio)molecules, particularly modified (bio)molecules, particles, beads, and/or the determination of the length/size (e.g. hydrodynamic radius) of individual (bio)molecules, particles, beads and/or the determination of length/size (e.g. hydrodynamic radius).