Light induced toxicity of merocyanine 540-silica nanoparticle complex

The electrostatic binding between the negatively charged lipophilic dye Merocyanine 540 and silica nanoparticles having 3-amino propyl groups at the surface has been characterized using absorption and fluorescence spectroscopy. The binding of the dye with the nanoparticle resulted in significant changes in its absorption spectra. Further the fluorescence intensity and lifetime gets enhanced by more than an order of magnitude. The results obtained suggest that this is due to the reduced photoisomerization rate of the dye bound to the nanoparticle. Consistent with the expectation that a reduction in the photoisomerization rate should enhance the singlet oxygen yield of the dye via intersystem crossing, the light induced toxicity of the dye-nanoparticle complex (tested with MCF cells) was observed to be higher compared to the free dye.