Comprehensive studies on the interaction of copper nanoparticles with bovine serum albumin using various spectroscopies.

Copper nanoparticles (NPs) of average size of ~7.5nm were synthesized by chemical reduction method. Fluorescence spectroscopy in synchronous and polarization modes were used to examine the nature of interaction between Cu NPs and bovine serum albumin (BSA) at different temperatures. Fluorescence quenching results suggest that Cu NPs interact with BSA molecule through static mechanism, as inferred from the quenching of BSA fluorophore. The calculated thermodynamic parameters (ΔG°, ΔH°, and ΔS°) hint that the binding process occurs spontaneously by involving hydrophobic forces. Synchronous fluorescence spectra reveal that the interaction of Cu NPs with BSA mostly changes the microenvironment of tryptophan and not of tyrosine residues. The formation of BSA-Cu NPs ground state complex was also confirmed from the resonant light scattering and fluorescence polarization spectra. Circular dichroism and Raman spectra indicate that α-helicity of the BSA decreases due to the interaction with Cu NPs. It was also found that Cu NPs are located in the close proximity of BSA molecule, which transfer energy efficiently from the excited state of BSA fluorophore to the Cu NPs.