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.