The preparation of stimulus-responsive Pickering emulsion and its application in preparing microspheres

In this paper, we report a novel redox responsive water-in-oil Pickering emulsion stabilized by negatively charged SiO2 nanoparticles hydrophobized with a trace amount of cationic surfactant 3-pyridyl-5-ferrocenyl-2-pyrazoline (PFP), in which ferrocene serves as a redox-sensitive group. The stability of Pickering emulsion can be modulated by adding oxidant and reducing agent alternatively, which leads to the change of amphiphilicity of SiO2 nanoparticles because of the adsorption of PF+P and desorption of PFP. This destabilization-stabilization behavior can be cycled at least three times, demonstrating that the Pickering emulsion is switchable. At the same time, polyacrylamide@SiO2-PF+P microspheres are prepared using Pickering emulsion as template, which can be used for the detection of Fe3+. Interestingly, when extremely small amounts of microspheres are placed in Fe3+ solution and left overnight, the limit of detection (LOD) decreases significantly because of the synergistic effect of enrichment and fluorescent probe for polyacrylamide and PF+P respectively. Moreover, the fluorescence intensity increased when EDTA was added to the solution containing microspheres and Fe3+, and a decrease of fluorescence intensity was observed when Fe3+ was added again, indicating that the composite microspheres could be reused. This work provides a promising way to construct novel fluorescent probes.