Surfactant-induced fluorescence changes in fluorescein dye

Synopsis Addition of non-ionic surfactants revealed changes in the visible absorbance and fluorescence characteristics of fluorescein dyes. Non-ionic surfactants induced a shift in Delta(max), towards shorter wavelengths along with a decrease in absorbance of the dye. On the other hand, addition of anionic surfactants induced a shift of Delta(max), towards longer wavelengths along with enhancement in absorbance and fluorescence. The absorbance value decreased initially, but increased on further addition of cationic surfactant, whereas fluorescence increased initially but decreased on further addition of cationic surfactant. These changes are attributed to the interaction of surfactant micelle with dye molecules, resulting in change of the coloured quinoid form to the colourless lactone form and vice versa.