Carbon nanotubes (CNTs) are advanced nanoscale platforms for enzyme immobilization and targeted enzyme delivery. Covalently linking enzyme to CNT surfaces is challenged by the potential enzyme modification as well as the controlled release for delivery applications. Physical adsorption of the enzyme to CNT based on electrostatic and other non-bonding interactions avoids these barriers but suffers from leaching. A potential solution is to use Metal-organic framework (MOF) to stabilize enzymes on CNTs which does not require any enzyme chemical modification. MOFs also provide extra stability under harsh environments. A special MOF, Zeolitic Imidazolate Framework (ZIF), is pH-sensitive, making the controlled release of the immobilized enzyme possible. The challenge in using MOF/ZIF to stabilize enzymes on CNTs is to understand and fine-tune the properties of enzymes, such as orientation, conformation, and distribution in the CNT/MOF composites. This is a non-trivial task for most biophysical technique because of the complexities caused by the background signals of CNT and ZIF, as well as the interactions between the enzyme and the platform. In this work, we report, for the first time, the preparation of enzyme/CNT/ZIF nanocomposites. In addition, we utilize a unique technique, Site-Directed Spin Labeling (SDSL) in combination with Electron Paramagnetic Resonance (EPR) spectroscopy, which is immune to aforementioned technical barriers, to probe the structural insights of the enzyme in the composites. For proof-of-concept, we employed two model enzymes, lysozyme, and amylase, for our studies. In comparison to CNT only, we found enhanced restriction and stability of lysozyme on CNT in the presence of ZIF as confirmed by a set of biophysical tools. Activity assays also confirmed that both enzymes are active on CNT/ZIF composites. The results are informative for guiding the rational design of CNT/ZIF combinations to improve stabilization, loading capacity, and catalytic efficiency.

Stabilizing enzyme on carbon nanotubes with metal-organic frameworks for enzyme delivery and biocatalysis applications

2019 Spring National Meeting

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