Influence of bovine serum albumin (BSA) on photodynamic properties of meso-tetrakis(sulfonatophenyl) porphyrin (TPPS4) for picosecond pulse trains

Due to the special interest and unique advantage of bovine serum albumin among various proteins, we carried out researches into effects of bovine serum albumin on photophysical characters of meso-tetrakis(sulfonatophenyl) porphyrin. The laser source we chose is picosecond pulse trains containing 20 subpulses of 70 picoseconds width separating by 13 nanoseconds at 532 nanometers. The theoretical analysis was carried out with a generalized five-level model representing the molecular populating structure. The two-dimensional paraxial field combined with the rate equations was solved by Crank-Nicholson numerical method. The nonlinear optical absorption mechanism in porphyrin is mainly two-step two-photon absorption. We found meso-tetrakis(sulfonatophenyl) porphyrin always shows prominent optical limiting effects binding with or without bovine serum albumin. In the presence of bovine serum albumin, the photophysical parameters of porphyrin get certain influence and cause slight weakening of optical limiting for porphyrin.