The changes in the nonlinear absorption of meso-tetrakis (p-sulfonatophenyl) porphyrin (TPPS4) caused by its binding to bovine serum albumin (BSA) were investigated in aqueous solutions. The nonlinear absorption depended on the excitation wavelength and pH. It is noteworthy that, for excitation at 640 nm, saturated absorption was observed in a TPPS4 solution (pH 4.0), whereas reverse saturated absorption occurred for all pH values from 4.0 to 7.0 when BSA was added to TPPS4. The presence of BSA also initiates an increase in the saturation intensity and a reduction of the nonlinear absorption coefficient. The interpretation of the results based on the binding of TPPS4 to BSA is corroborated by linear absorption, fluorescence, light scattering, and flash-photolysis data.
© 2000 Optical Society of America
Original Manuscript: September 19, 1999
Revised Manuscript: April 21, 2000
Published: August 20, 2000
Iouri E. Borissevitch, Nikifor Rakov, Glauco S. Maciel, and Cid B. de Araújo, "Changes in porphyrin nonlinear absorption owing to interaction with bovine serum albumin," Appl. Opt. 39, 4431-4435 (2000)