Electrochemical and Biocatalytic Signal-Controlled Payload Release from a Metal-Organic Framework.

A metal-organic framework (MOF), ZIF-8, which is stable at neutral and slightly basic pH values in aqueous solutions and destabilized/dissolved under acidic conditions w as loaded with a pH-insensitive fluorescent dye, rhodamine-B isothiocyanate, as a model payload species. Then, the MOF species w ere immobilized at an electrode surface. The local (interfacial) pH value w as rapidly decreased by means of an electrochemically stimulated ascorbate oxidation at +0.4 V (Ag/AgCl/KCl). Oxygen reduction upon switching the applied potential to -0.8 V, allowed to return the local pH to the neutral/basic pH, then stopping rapidly the release process. The developed method allowed electrochemical control over stimulated or inhibited payload release processes from the MOF. The pH variation proceeded in a thin film of the solution near the electrode surface. The switchable release process w as realized in a buffer solution and undiluted human serum. As the second option, the pH decrease stimulating the release process w as achieved upon an enzymatic reaction using esterase and ester substrate. This approach potentially allows the release activation controlled by numerous enzymes assembled in complex biocatalytic cascades. It is expected that related electrochemical or biocatalytic systems can represent novel signal-responding materials with the switchable features for delivering (bio)molecules within biomedical applications. This article is protected by copyright. All rights reserved.