2008 NSTI Nanotechnology Conference and Trade Show - Nanotech 2008 - 11th Annual

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Clean Technology 2008

Fabrication of Highly Dispersible Single Wall Carbon Nanoubes-Polymer Composite for Bioanalytical Devices

P. Zhang, D.B. Henthorn
University of Missouri-Rolla, US

Keywords:
carbon nanotube, polymer, enzyme

Abstract:
A considerable amount of research has been devoted to carbon nanotubes because of their unique electrical and chemical properties. One of the most promising applications for carbon nanotubes is as a support material for bioanalytical devices. Immobilization of enzymes or other proteins on single wall carbon nanotubes allow researchers to couple the molecular recognition ability of these biomolecules with the unique optical and electrical properties of CNTs. We aim to develop a novel method that maximizes enzyme loading and retains enzymatic activity while simultaneously adding to the biocompatibility and dispersability of the nanotube structures. In this work, we successfully used an ultraviolet light initiated “graft from” polymerization method to fabricate single wall carbon nanotubes with pendant polymer chains of various functionalities, including poly(ethylene glycol) chains to boost dispersability, and pendant epoxy groups as protein conjugation sites. Polyethylene glycol monomethacrylate (PEGMA) and glycidyl methacrylate (GMA) monomers were copolymerized directly from the sidewall of carbon nanotubes after the surface immobilization of photoinitiator. The use of the PEGMA monomer greatly enhanced dispersability, while the epoxide group belonging to GMA can be used as a reactive site for coupling with various species (enzymes, proteins, macromolecules, etc.) through a number of different reactions. A model enzyme, alkaline phosphatase, was used to study the loading efficiency as well as the retention of enzymatic activity. Samples with various ratios of the two monomers were fabricated to optimize their use in aqueous environments, and an optimum formula of the composition was developed. While significant loading occurred on nanotubes with grafted polymer chains rich in the GMA monomer, dispersability was poor. Addition of pendant PEG chains boosted dispersability in aqueous media. Enzyme loading amount and retention activity were improved compared to the work done by other groups [1] and recent work in our laboratory. More importantly, no enzyme precipitation was observed from the carbon nanotube-enzyme complex [2]. Thermogravimetric analysis (TGA) confirmed the efficiency of the polymerization process (Figure 1) and showed that significant mass is added during the graft polymerization. Atomic force microscopy (AFM) was used to image enzyme-nanotube conjugates, with the ease of dispersability readily seen in images (Figure 2).


Nanotech 2008 Conference Program Abstract