α-amylase binding to thermal plasma synthesized zinc oxide nanosheets: A fluorescence study

Zinc oxide (ZnO) nanosheets were synthesized using thermal plasma method, and characterized by X-ray diffraction and Transmission electron microscopy, to investigate their interaction with α-amylase at different pH, temperature and incubation time. Fluorescence quenching, synchronous and UV-visible spectroscopy were employed to establish the mechanism of interaction between ZnO nanosheets and α-amylase at different experimental condition. The obtained results confirmed that the ZnO nanosheets (≈25 nm) quench the fluorophore of α-amylase by forming ground state complex in the reaction mixture. The thermodynamic parameters were determined by using fluorescence quenching data. The free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) suggest that the binding process occurs spontaneously by involving hydrogen bond and van der Waals interaction. The synchronous spectra reveal that the microenvironment close to both tyrosine and tryptophan residues of α-amylase was perturbed and that the increased in hydrophobicity of both the residues in the presence of ZnO nanosheets. Resonance light scattering phenomenon suggests that α-amylase-ZnO complex are formed and conformational changes occurred in amylase. The changes in microenvironment around tyrosine and tryptophan suggest by synchronous and resonance light scattering spectra at various pH, temperature and incubation time.