Au Nanoparticle-Based Surface Energy Transfer Probe for Conformational Changes of BSA Protein

In the present study, Au nanoparticle based surface energy transfer (SET) has been used to measure conformational changes in proteins. A significant photoluminescence (PL) quenching (91−97%) of tryptophan intensities of bovine serum albumin (BSA) protein is observed in the presence of Au nanoparticles, and the measured distances (r) between the donor (tryptophan) and the acceptor (Au nanoparticle) are 27.0, 22.9, and 25.7 Å for E, N, and B forms of BSA protein, respectively. Results indicate that Au nanoparticle quenches BSA fluorescence mainly through a static quenching mechanism. Analysis suggests that binding constant and bound/unbound ratio varies with changing the conformation of protein. The PL quenching of dye varies from 47.2 to 86.6% with changing the conformation of protein without changing the radiative rate of dye. The measured distances (d) between the donor (dye) and the acceptor (Au nanoparticle) are 116.5, 76.1, and 86.4 Å for E, N, and B forms of BSA protein, respectively, using the efficiency of surface energy transfer (SET) which follows 1/d4 distance dependence. The estimated radii of different conformations of the protein nicely match with the reported values of hydrodynamic radii of different conformations of BSA protein. Therefore, such bioconjugated Au nanoparticle based surface energy transfer should have great potentials for optical-based molecular ruler.