Spectroscopic studies on the interactions of capped CdS quantum dots with human serum albumin (HSA) and bovine serum albumin (BSA)

A polyacrylamide grafted onto kappa-carrageenan biopolymer (κC-g-PAAm) was successfully synthesized and employed for coating of CdS quantum dots (QDs) in aqueous solutions. The as-obtained QDs were characterized by Fourier transform infrared (FT-IR), transmission electron microscopy (TEM), UV-visible (UV–vis), and fluorescence spectroscopy. The average size of CdS-κC-g-PAAm QDs was about 2.5 nm. After that, the interaction of coated QDs with human serum albumin (HSA) and bovine serum albumin (BSA) was investigated under the simulative physiological conditions (Tris-HCl buffer, pH 7.4). Fluorescence analysis at different temperatures revealed the gradual quenching of both proteins by titration with coated QDs. The results showed a single class of binding site and a static quenching mechanism between coated QDs and the proteins. The distance between coated QDs and the proteins was evaluated according to the theory of Föster energy transfer. The thermodynamic parameters, free energy change(ΔG), enthalpy change (ΔH), and entropy change (ΔS) for coated QDs-HSA (or BSA) were calculated according to van't Hoff equation, and the results indicated the major roles of van der Waals forces and hydrogen bonds in these interactions. The results of cyclic voltammograms (CVs) and FT-IR spectra affirmed the complex formation between the synthesized QDs and HSA (or BSA).