Theranostics, i.e. the incorporation of diagnosis and therapy into a single nanoplatform, opens many new possibilities in the battle against cancer, which is one of the main death causes in the EU. In this project, we aim to develop a biodegradable multifunctional hybrid nanostructure that combines cancer detection through temperature measurement in the near-infrared, and treatment through simultaneous photothermal therapy (PTT) and chemotherapy with doxorubicin (DOX). The nanothermometers would also be important for temperature monitoring during PTT, to ensure that healthy cells are not damaged. This designed nanostructure is a sandwich core-shell hybrid nanomaterial, where the K3ZrF7:Nd,Yb nanothermometer core is covered with an intermediate organosilica shell decorated with the CuS nanoheaters. They are covered with thermoresponsive polymers releasing DOX at temperatures above 37 °C. The additional beauty of this novel hybrid nanostructure is that it is composed of biocompatible and biodegradable materials that decompose into non-toxic, easily excretable components, avoiding toxicity issues related to bioaccumulation in organs.