Inverse Pickering Emulsion Stabilized by Binary Particles with Contrasting Characteristics and Functionality for Interfacial Biocatalysis.

Water-in-oil (w/o) Pickering emulsions have received considerable attention in biphasic enzymatic catalysis for their advantages of good stability, large interfacial area, and ease of product separation. However, enzymes are commonly encapsulated in the interior of aqueous droplets, which inevitably increases the diffusional resistance to catalysis. Alternatively, enzymes are immobilized or trapped into Pickering stabilizers. Often, however, these approaches suffer from leaching and a decrease of enzyme activity during the chemical treatments. We report here a new Pickering interfacial biocatalysis platform with efficient enzyme encapsulation, binary particle composition, and high catalytic performance. Our approach is based on w/o Pickering emulsions stabilized by binary particles consisting of hard silica and soft, pH-responsive microgel particles. We demonstrate that pH-responsive microgels can simultaneously stabilize a w/o Pickering emulsion, encapsulate enzymes, and catalyze reactions at the water/oil interface. In addition, we show that the coordination with rigid silica nanoparticles as additional stabilizers markedly improves the emulsion structure and will provide a new avenue for the preparation of w/o Pickering emulsion and concept of biphasic catalysis.