Thermal mapping in biological membranes could unlock and help us understand many chemical and physical processes that do not only pertain to localized membrane phenomena but also extend to many other intra- and extracellular pathways. In this manuscript, we report the development of a ratiometric thermal fluorescent probe based on the Forster resonance energy transfer between a lipid-embedded conjugated polyelectrolyte and a lyophilic acceptor dye. We showed that the Forster resonance energy transfer (FRET) pair is sensitive within the relevant physiological temperature window (20.0-50.0 degrees C). The signal was also shielded from an external pH and stable when cycled multiple times. The probe was also sensitive to the membrane composition and could, therefore, be further developed to probe the membrane composition and viscosity.