Insight of MOF Environment-Dependent Enzyme Activity via MOFs-in-Nanochannels Configuration

Maintaining the high activity of an enzyme is a fundamental requirement to widen the application of metal-organic frameworks (MOFs) in the biotechnology, biosensor, and biomedicine fields. However, it is still challenging to monitor and understand an MOF environment-related activity for an enzyme. Here, we developed a MOFs-in-nanochannels configuration for broadening the biocatalytic activity of an enzyme in MOFs on demand. ZIF-8 [Zn(mim)₂, Hmim = 2-methylimidazolated] grown in TiO₂ nanochannels is used as the platform, and cytochrome C (CytC) is used as a model enzyme encapsulated in ZIF-8. The enzymatic catalytic process converts 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) to a positively charged product (ABTS⁺). On the basis of current-voltage properties, the change of ion transport characteristics in nanochannels can be monitored with time. The ZIF-8 encapsulating CytC molecules not only exhibit a significantly enhanced enzymatic activity in a wide temperature region (37-80 °C) but also have remarkably long storage stability at room temperature. The results of quantum mechanical calculation indicate that the Fe-S bond of CytC is inclined to break in the environment of ZIF-8 owing to the confinement effect of the MOF structure, favorable for enzymatic catalysis. The MOFs-in-nanochannel configuration provides an innovative and label-free design for the onsite monitoring of catalytic activity of an enzyme in MOFs, which holds great potential in constructing biosensing platforms with remarkable performance and stability.