Interaction of gold nanoparticles with protein: A spectroscopic study to monitor protein conformational changes

Gold nanoparticles (GNPs) conjugated with biomolecules are promising building blocks for assembly into nanostructured functional materials for developing biomarker platforms because of their size dependent optical and electrical properties. Biocompatible GNPs were synthesized using glutamic acid as a reducing agent and the interaction between bovine serum albumin (BSA) and GNPs was investigated using fluorescence and circular dichroism (CD) spectroscopies. The binding constant (Kb) of protein (BSA) to GNPs was determined by measuring the quenching of the fluorescence intensity of tryptophan residues of the protein molecules after conjugation. The conformational change in BSA at its native form after conjugation with GNPs confirmed that protein undergoes a more flexible conformational state on the boundary surface of GNPs after bioconjugation. The CD studies further showed a decrease in the α-helical content after conjugation. The results confirmed that the change in conformation was larger at higher concentrations of GNPs.