A facile synthesis procedure was reported to synthesize homogenous dispersed CdS QDs inside CTS. It requires mild synthesis conditions and is a one-pot synthesis procedure. The functional groups of biopolymer chitosan CTS were potential matrices to grow CdS QDs via an in-situ approach with a narrow size distribution (1-7 nm). The synthesized CdS/CTS exhibits good photophysical properties. Heavy metal ions (Cd after coordination, formation of CdS, and Cu after adsorption into CdS/CTS) improved the thermal properties of pure CTS. CdS/CTS can selectively interact with Cu 2+ ions offering naked-eyes detection. The data analysis provides a comprehensive, in-depth discussion of the interaction between heavy metal ions and CdS/CTS QDs.