Systematic investigation on the interaction of bovine serum albumin with ZnO nanoparticles using fluorescence spectroscopy

Zinc oxide (ZnO) nanoparticles with average size of ∼7.5 nm were synthesized to investigate their interaction with bovine serum albumin (BSA) at different temperatures. Fluorescence quenching, synchronous and polarization spectroscopy along with UV–vis absorption, circular dichroism and resonance light scattering spectroscopy techniques were used to establish the interaction mechanism between ZnO and BSA. The obtained results confirmed that the ZnO nanoparticles (NPs) quench the fluorophore of BSA by forming ground state complex in the solution. The fluorescence quenching data was also used to determine binding sites and binding constants at different temperatures. The calculated thermodynamic parameters (ΔG°, ΔH°, and ΔS°) suggest that the binding process occurs spontaneously by involving hydrogen bond and van der Waals interactions. The synchronous fluorescence spectra reveal that the microenvironment close to both the tyrosine and tryptophan residues of BSA is perturbed and that the hydrophobicity of both the residues is increased in the presence of ZnO NPs. Resonance light scattering, circular dichroism, and fluorescence polarization spectra suggest the formation of BSA–ZnO complex and conformational changes in BSA. The calculated distance between the BSA and ZnO NPs suggests that the energy transfer from excited state of BSA to ZnO NPs occurs with high efficiency.