Spectroscopic studies on the interaction between CdTe nanoparticles and lysozyme

Nanoparticles of cadmium telluride (CdTe) coated with thioglycolic acid (TGA) were prepared in the water phase. The interaction between CdTe nanoparticles (NPs) and lysozyme (Lyz) was investigated by fluorescence and circular dichroism (CD) spectroscopy at pH 7.40. It was proved that the fluorescence quenching of Lyz by CdTe NPs was mainly a result of the formation of CdTe–Lyz complex. By the fluorescence quenching results, the Stern–Volmer quenching constant (KSV), binding constant (Ka) and binding sites (n) were calculated. The binding distance (r) between Lyz (the donor) and CdTe NPs (the acceptor) was obtained according to fluorescence resonance energy transfer (FRET). Gradual addition of CdTe NPs to the solution of Lyz led to a marked increase in fluorescence polarization (P) of Lyz, which indicated that CdTe NPs were located in a restricted environment of Lyz. The effect of CdTe NPs on the conformation of Lyz has been analyzed by means of synchronous fluorescence spectra and CD spectra, which provided the evidence that the secondary structure of Lyz has been changed by the interaction of CdTe NPs with Lyz.