The effects of surface potential on the binding and fluorescence of 1 anilinonaphthalene 8 sulfonate (ANS) in suspensions of bacteriorhodopsin are investigated. The ANS binding depends on the surface potential which modulates the apparent binding constant of ANS on the bR membrane. The surface potential of the binding ANS measured in energized is larger than in nonenergized bR membrane. In the laser four wave mixing experiment, the saturation density and the length of exitons are obtained under the one-dimensional exciton phase space filling model. The values result in improving the highly efficient energy transfer from the aromatic amino acids of bR to the bound ANS and in raising the density of the surface charge of the energized bR so that the non radiation resonant transfer is made to be exciton transfer, and the surface potential of energized bR has its nonlinear optical mechanism.