Polydiacetylene-coated gold nanoparticles as a novel plasmonic thermosensor based on the phase transition of the outer shell

•A core–shell nanostructure was synthesized and characterized to act as plasmonic thermosensor.•The outer shell made by poly((10,12-pentacosadiynoic acid) undergoes phase transitions that induce significant and reproducible temperature effects.•The response functions in terms of SERS signaling afford temperature sensitivity and a working range suitable for in vivo and in vitro diagnostic applications.•The construction of accurate and transferable calibration curves is demonstrated.•VT-SERS measurements represent a powerful method for the characterization of ultrathin polymer films.