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, is loaded with a pH-insensitive fluorescent dye, rhodamine-B isothiocyanate, as a model payload species. Then, the MOF species are immobilized at an electrode surface. The local (interfacial) pH value is 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 allows to return the local pH to the neutral/basic pH, then stopping rapidly the release process. The developed method allows electrochemical control over stimulated or inhibited payload release processes from the MOF. The pH variation proceeds in a thin film of the solution near the electrode surface. The switchable release process is realized in a buffer solution and undiluted human serum. As the second option, the pH decrease stimulating the release process is 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 switchable features for delivering (bio)molecules within biomedical applications. A metal-organic framework (MOF), ZIF-8, which is stable at neutral pH in aqueous solutions and dissolves under acidic conditions, is loaded with a fluorescent dye as a model payload species. The pH is decreased by electrochemical or biocatalytic reactions resulting in the MOF dissolution and the payload release. The studied systems represent signal-responding materials for delivering (bio)molecules within biomedical applications.image

Automated summary

This study investigates a metal-organic framework (MOF) called ZIF-8, which remains stable in neutral pH aqueous solutions but dissolves under acidic conditions. By electrochemical or enzymatic reactions, the pH can be decreased to induce MOF dissolution and payload release. The results suggest that signal-responsive materials with switchable features can be used to deliver biomolecules in biomedical applications.