Facile surface functionalization of multiwalled carbon nanotubes by soft dielectric barrier discharge plasma: Generate compatible interface for lipase immobilization

• MWCNTs was surface-functionalized by simple, easy and fast DBD plasma treatment.
• The functionalized molecular species were confirmed by FTIR and XPS analyses.
• Adsorption of CRL on different functionalized MWCNTs displayed different patterns.
• Immobilization of CRL on functionalized MWCNTs was clearly viewed with AFM imaging.
• Immobilized CRL on alkylamidated MWCNTs showed excellent reusability and stability.

To create compatible interface for enzyme immobilization, the surface of multi-walled carbon nanotubes (MWCNTs) was functionalized using soft technique dielectric barrier discharge plasma (DBDP) for carboxylation and amination; followed by further amidation of carboxyl group with alkylamine. Successful functionalization and enzyme immobilization were structurally confirmed using spectroscopic analysis Fourier-Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS). The immobilization of Candida rugosa lipase (CRL) on functionalized MWCNTs was evidenced by clearly viewing with Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM) imaging. CRL showed more Freundlich equilibrium behavior upon immobilization on annealed and octadecylamidated MWCNTs, which suggested a multilayer adsorption; while upon physical adsorption on aminated and carboxylated MWCNTs, CRL, to more extent, demonstrated a Langmuir equilibrium property, producing an enzyme monolayer. It was proven that DBDP-mediated surface-functionalization could create compatible microenvironments for enzyme immobilization, resulted in improved specific activity and thermostability. The immobilized CRL on octadecylamidated MWCNTs displayed excellent reusability and operation stability, indicating its potential for industrial application.