AbstractThe fluorescence quenching spectrum of bovine serum albumin (BSA) was investigated in the presence of felodipine (FLD) by spectroscopic methods including fluorescence spectroscopy and UV–Vis absorption spectroscopy. Stern–Volmer quenching was successfully applied and the corresponding thermodynamic parameters, namely enthalpy change (ΔH), free energy change (ΔG) and entropy change (ΔS) at different temperatures (304, 314 and 324 K) were calculated according to the Van't Hoff relation. This revealed that the hydrophobic interaction plays a major role in stabilizing the complex. The fluorescence spectrum of BSA was studied in presence of various concentrations of SDS surfactant. The distance (r) between donor (BSA) and acceptor (FLD) was obtained according to fluorescence resonance energy transfer (FRET). The synchronous fluorescence spectroscopy was used to investigate the effect of FLD on BSA molecule. The result shows that the conformation of BSA was changed in the presence of felodipine. Copyright © 2009 John Wiley & Sons, Ltd.