Binding investigation on the interaction between Methylene Blue (MB)/TiO2 nanocomposites and bovine serum albumin by resonance light-scattering (RLS) technique and fluorescence spectroscopy

The interaction between Methylene Blue (MB)/TiO2 nanocomposites and bovine serum albumin (BSA) was investigated by resonance light scattering (RLS), fluorescence, three-dimension spectra and UV–vis absorbance spectroscopy. Several factors which may influence the RLS intensity were also investigated before characterizing MB/TiO2–BSA complex. It was proved that the mechanism of MB/TiO2 nanocomposites binding to BSA was mainly a result of the formation of MB/TiO2–BSA complex. The binding constant of MB/TiO2–BSA is 0.762 × 10−5 L mol−1 at 298 K. By calculating the binding constant at different temperature, the thermodynamic parameters ΔH, ΔG, and ΔS can be observed and deduced that the hydrophobic interactions played an important role to stabilize the complex. The distance r (3.73 nm) between donor (BSA) and acceptor (MB/TiO2) was obtained according to fluorescence resonance energy transfer (FRET). The binding site for MB/TiO2 on BSA was mainly located in sub-domain IIA. The UV–vis absorbance, circular dichroism and three dimension fluorescence have also been used to investigate the effect of MB/TiO2 on the conformation of BSA.