Systematically investigations of conformation and thermodynamics of HSA adsorbed to different sizes of CdTe quantum dots

Fluorescent quantum dots (QDs) have attracted great attention in biological and biomedical fields. In particular, for any potential application, the interaction of QDs with some biomolecules is much important. Herein, the interactions between QDs with different sizes and human serum albumin (HSA) were systematically investigated by UV–vis absorption spectra, fluorescence spectra and circular dichroism (CD) spectra under the physiological conditions. Four sizes of CdTe QDs with maximum emission of 520 nm (green QDs, GQDs), 568 nm (yellow QDs, YQDs), 620 nm (red QDs, RQDs) and 680 nm (crimson QDs, CQDs) were tested. The fluorescence spectra results indicated that QDs could quench the fluorescence intensity of HSA effectively with a size-dependent relationship. The binding of QDs and HSA is a result of the formation of QDs–HSA complex and the electrostatic interaction plays a major role in stabilizing the complex. The modified Stern–Volmer quenching constants Ka at different temperatures and corresponding thermodynamic parameters ΔH, ΔG and ΔS were calculated. The conformational changes of HSA induced by QDs have been analyzed by CD spectra, and the results indicated that the biological activity of HSA was weakened in the present of QDs with bigger size.