Furthermore, there is an overlap between N 1s and Cd 3d. However, the quantitative analysis ensures the presence of a high concentration of Cu in Cu_CdS/CTS due to the replacement with Cd in CdS and the coordination with the functional groups of CTS (Figure ). The mechanism can be explained due to the strong binding of Cu 2+ onto the surface of CdS and the functional groups of CTS, resulting in the formation of CuS on the external surface of the CdS QDs . The elemental analysis and mapping for Cu_CdS/CTS are characterized further using EDX analysis and mapping (Figure ). EDX analysis (Figure ) confirms the presence of Cu, Cd, and S in Cu_CdS/CTS, which agrees with XPS analysis data (Figure ). The elemental mapping of C, N, S, Cd, and Cu ensures the well dispersion of Cu_CdS inside CTS (Figure ). STEM images indicate the homogenous distribution of Cu_CdS inside CTS frameworks (Figure ). Chitosan offers several advantages of being a suitable biopolymer to synthesize CdS-based QDs. It formed complexes with Cd 2+ ions via coordination during the in-situ growth of CdS QDs. Chitosan's functional groups, such as amino and hydroxyl, serve as influential capping functional groups for CdS QDs. The viscosity of CTS solution during the in-situ growth of CdS prevents the aggregation and agglomeration of QDs offering high dispersion of QDs into the CTS matrix. The functional groups of CTS can be selectively bound to Cu 2+ ions offering selective sensing compared to other heavy metal ions. CTS plays several roles; 1) modulator during the in-situ growth of CdS QDs; 2) stabilizer for CdS; and chelator for heavy metal ions with high selectivity toward Cu 2+ ions. The prepared materials, i.e., CdS/CTS or Cu_CdS/CTS, seem promising for further biosensing, photocatalysis, and energy-based applications.