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

Abstract

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.