Behavioral difference of interactions between photosensitizer MC 540 and serum albumins in anionic AOT and cationic CTAB reverse micelles

MC 540 is a very efficient photosensitizer (PS) in photodynamic therapy (PDT) mainly used in the treatment of different types of melanoma cells. It mainly generates singlet oxygen (1O2) as a reactive oxygen species (ROS) during PDT. Application of PDT in deep tissues mainly restricted by limited penetration depth of visible light required for activating the PS. To activate MC 540, either binds it with some other component like upconverting nanoparticles (UCNs) or use some other sources of light like X-ray. So how this efficient PS behaves photochemically in an in vitro environment (HSA and BSA with aerosol-OT (AOT) and cetyltrimethylammonium bromide (CTAB)), studied by different spectroscopic techniques. In AOT RMs, on addition of MC 540 there is no wavelength shift of fluorescence maximum of HSA; however for BSA a red shift occurs. However, in CTAB RMs both the SAs show the red shift with increasing concentration of MC 540. The variation of binding constant with temperature is much more prominent in BSA than HSA may be due to the structural rigidity of BSA. The binding constants are less in RMs than in buffer. All the interactions are spontaneous and entropy driven. The entropy change is significant in AOT RMs. The fluorescence lifetime of MC 540 increases from buffer to RMs. With increasing w0 of RMs the lifetime of MC 540 gradually decreases. The fluorescence lifetime of SAs decreases quite significantly in buffer compared to both cationic and anionic RMs. Dynamic light scattering supports the position of SAs inside RMs in the absence and presence of MC 540.