CdS/CTS QDs were synthesized via mild hydrothermal conditions followed by a freeze-drying procedure. The chitosan solution was prepared via dissolving chitosan (0.1 g) in H2O (20 mL) containing acetic acid (1 wt.%). Cd(NO3)2 (11 mg) was added to the chitosan solution. The solution was subjected to continuous stirring for 24 h to ensure the coordination between Cd 2+ ions and the functional groups of CTS. A fresh solution of Na2S (12 mg, 10 mL H2O) was added dropwise. A solution of NH4OH (40 wt.%) was added to obtain the solution's pH of 10. The solution was stirred at 90 °C until all excess ammonia evaporated from the solution. The prepared CdS/CTS QDs (10 mg) were then dispersed into an aqueous solution (10 mL, 1 mg/mL) using ultrasonication.