Redox-Responsive Pickering Emulsions Based on Silica Nanoparticles and Electrochemical Active Fluorescent Molecules

In this paper, we report a novel redox-responsive water-in-oil Pickering emulsion stabilized by negatively charged silica nanoparticles in combination with a trace amount of redox switchable fluorescent molecule ferrocene azine (FcA), in which ferrocene serves as a redox-sensitive group and anthryl unit serves as a fluorescence emission center. By alternately adding oxidants and reducing agents at a moderate condition, the amphiphilicity of silica nanoparticles changes because of the adsorption of Fc⁺A and the desorption of FcA on the silica surface. On the one hand, the stability of emulsions can be transformed between stable and unstable at ambient temperature via redox trigger and the regulation process can be cycled at least three times. On the other hand, the fluorescent intensity of the FcA molecule can be regulated by redox stimuli; thus, the change in fluorescent behavior of the emulsion droplets is observed upon redox cycles, which makes it useful in the fluorescent label of stimuli-responsive Pickering emulsions. This work provides a deep understanding of the regulation mechanism of Pickering emulsions upon redox stimuli and opens the new way for in situ fluorescent label of stimulus-responsive Pickering emulsions without introducing additional fluorescent molecules.