“…11,12 Like Raman spectroscopy, PhI is an all optical method, and it is based on the detection of refractive index variations that are induced by photothermal effect in the local environment of an absorbing nanoparticle. 13,14 A few variants of PhI exist, 13,15,16 and photothermal heterodyne imaging, which is the most sensitive scheme, 13,17 allows detecting several types of nano-objects at a single particle level. These include gold nanoparticles, even within a cell matrix and for membrane receptor dynamics studies in live cells, 18,19 molecules, quantum dots or single walled carbon nanotubes.…”