Luminescent cadmium sulfide quantum dots based on calix[4]arene supramolecular structures: optical, fluorescent, and antibacterial properties

Abstract Water-soluble luminescent cadmium sulfide quantum dots (CdS QDs) capped with thioglycolic acid were synthesized in an aqueous medium. The hydrodynamic diameter of the produced CdS QDs in aqueous solution was measured to be 5.16 nm using dynamic light scattering techniques, which closely aligns with high-resolution transmission electron microscopy. The optical band gap of the synthesized CdS QDs was determined to be 4.39 eV, which is greater than that of bulk CdS. Structural analyzes were conducted utilizing powder x-ray diffraction, which validated the cubic phase of CdS. A unique hybrid organic–inorganic molecular assembly (CdS@PBCD and CdS@PSC) has been synthesized by integrating CdS QDs with supramolecular compounds, specifically p-tert-butyl calix[4]arene di acid (PBCD) and p-sulfonatocalix[4]arene (PSC). Furthermore, we investigated how interactions with amino acids influenced the fluorescence characteristics of the CdS@PSC and CdS@PBCD molecular complexes. A significant enhancement in fluorescence was noted for the tryptophan CdS@PSC composite upon interaction with all tested amino acids. The synergistic assembly of these structures led to a marked increase in fluorescence emission, facilitating the measurement of DL-tryptophan over a broad concentration range. This resulted in a calibration curve exhibiting high linearity ( R 2 ≈ 0.99). The Stern–Volmer plot indicated that the limit of detection and limit of quantification were determined to be 19.2 ppm and 58.4 ppm, respectively. Furthermore, the antibacterial properties of CdS QDs, CdS@PBCD and CdS@PSC were assessed against microorganisms, revealing that CdS@PBCD exhibited lower toxicity.