The electrochemical behavior of core-shell CdSe/CdS magic-sized quantum dots linked to cyclodextrin for studies of the encapsulation of bioactive compounds

Semiconductor nanocrystal quantum dots have been the subject of extensive investigations in different areas of science and technology in the past years. In particular, there are few studies of magic-sized quantum dots (MSQDs), even though they exhibit features such as extremely small size, fluorescence quantum efficiency, molar absorptivity greater than traditional QDs, and highly stable luminescence in HeLa cell cultures, thereby enabling monitoring of biological or chemical processes. The present study investigated the electrochemical behavior of free CdSe/CdS MSQDs using glassy carbon electrode and CdSe/CdS MSQDs immobilized on a gold electrode modified with a self-assembled cyclodextrin monolayer. The MSQDs showed two peaks in aprotic medium. The functionalized film modifier was prepared and characterized by means of cyclic voltammetry and electrochemical impedance spectroscopy using ferricyanide ions as a redox probe. The prepared modified electrode exhibited a stable behavior. The proposed method was successfully applied to encapsulation studies of mangiferin, a natural antioxidant compound, and cyclodextrin associated with the quantum dot, and the response was compared with that of the modified electrode without QD. The fluorescence study revealed that CdSe/CdS quantum dots emit blue light when excited by an optical source of wavelength of 350 nm and a significant increase in fluorescence and absorbance intensity is observed from the core-shell CdSe/CdS MSQDs when quantities of mangiferin are added to the solution containing thiolated cyclodextrin. CdSe/CdS MSQDs are optically and electrochemically sensitive and can be used for the detection and interaction of compounds encapsulated in cyclodextrin.