Using hydrogel microparticles to transfer hydrophilic nanoparticles and enzymes to organic media via stepwise solvent exchange.

We present a simple and versatile approach of using hydrogel microparticles to transfer both inorganic hydrophilic nanoparticles (NPs) such as CdTe quantum dots and enzymes such as lipase B from Candida antarctica (CalB) to organic media and eventually encapsulate them in the gel microparticles by consecutive exchange of the water swollen in the hydrogel microparticles with water-miscible organic solvents and water-immiscible solvents. The entrapment of hydrophilic nanoparticles is due to their incompatibility with water-immiscible organic solvents soaked in the gel matrices and in the surrounding environment, so the present approach obviates the need for any chemical modification to the NP surface or to the hydrogel and furthermore does not require any size matching or chemical affinity of the NPs for the hydrogel networks. The solvent exchange process causes little change of the intrinsic properties of hydrophilic nanoparticles; CdTe quantum dots encapsulated in hydrogel microparticles, dispersed in water-immiscible organic solvents, remain strongly fluorescent, and CalB retains high catalytic activity. Of importance is that the hydrophilic nanoparticles encapsulated in the gel microparticles in organic media can be completely recovered in aqueous media via reversed solvent exchange. As a consequence, the present approach should hold immense promise for technical applications, especially in catalysis.