Chemically reduced electrospun polyacrilonitrile–carbon nanotube nanofibers hydrogels as electrode material for bioelectrochemical applications
Introduction
Electrospinning is a powerful tool to form in high quantities well defined fibers with submicron diameters from many different types of organic or inorganic polymers [1]. Within these polymers, polyacrylonitrile (PAN) is one of the most used due to its high tensile strength, thermal and mechanical stability, and resistance toward solvent and abrasion [2]. Such nanosized fibers have great potentials for various types of applications like tissue or membrane engineering, or as high surface area support in biosensors [3], [4] or fuel cell devices [5]. In order to use these insulating nanofibers as electrode materials, the necessary conductivity can be obtained via carbonization after annealing processes [6], [7], [8], metallic coatings [9] or by choosing appropriate conductive fillers like metal particles or nanostructured carbon [10]. However, high loadings of such conductive materials can prevent fiber formation of homogeneously distributed diameters or can even short circuit the electrospinning setup. These limitations generally lead to poorly conductive fibers. Beside the possibility to form stable nanosized fibers, PAN has also the capacity to form hydrogels in water and became an important compound in biomedical electrophoresis [11]. Furthermore, the chemical transformation of the nitrile groups into NH2 functions can improve water absorption [12].
Here, we investigated the effect of hydrogel formation reduced PAN fibers on improved diffusion of small molecules like electroactive species. Carbon nanotube doped PAN (PAN–CNT) fibers were chemically reduced and the resulting amine groups served for both, anchor points for biomolecule immobilization and improved hydrogel formation. The potential of these fibers for the development of electroactive biomaterials in biosensors or biofuel cells was exemplified by a standard biosensor setup. Polyphenol oxidase (PPO) was used as bioreceptor unit model for the detection of catechol to evaluate the electroactivity of the CNT–Hydrogel fibers and the diffusion of the enzymatically formed o-quinone to the conductive CNT network.
Section snippets
Materials
Polyacrilonitrile (PAN, Mw = 150.000), N,N-dimethylformamide (DMF), (LiAlH4), diethyl ether (DET), glutaraldehyde, catechol, PPO (120 U mg−1), were purchased from Sigma–Aldrich and used without further purification. Commercial-grade thin multi-walled carbon nanotubes (MWCNT, 9.5 nm diameter, purity > 95%), obtained from nanocyl were used as received. Phosphate buffer solutions at different pH values were prepared with mono and dibasic phosphate (pH 6.5; 0.1 M).
Apparatus
All electrochemical experiments were
Morphology of the fibers
A photograph of each prepared fibers is shown in Fig. 1. As produced PAN fibers are shaped as a white tissue. In presence of CNT in these fibers, the tissue becomes dark gray but has the same macroscopic morphology as pure PAN fibers. It should be noted that various CNT loadings within the PAN fibers were examined. Taking into account that at CNT concentration higher than 0.5 wt%, no homogeneous fiber deposits were formed and even led to a short circuits during electrospinning, the formation of
Conclusion
Nanosized PAN–CNT composite fibers were electrospun in order to form an electroactive support with high surface area for applications in the field of biological sensors or enzymatic biofuel cells. The nitrile groups of fibers were chemically reduced into amines that were then activated by glutaraldehyde allowing thus the post-functionalization by a protein via its covalent binding.
In dry state all obtained and modified fibers are insulants. When immersed in aqueous solutions, these fibers swell
Acknowledgments
The authors would like to thank the platform ‘functionalization of surfaces and transduction’ of the scientific structure ‘Nanobio’ for providing facilities and Arielle Le Pellec for assistance. The authors also thank the PHC Utique program n° 30583QD (CMCU n° 14G1206), the “Bourse Alternance du Ministère de l’Enseignement Supérieur de la Recherche Scientifique”, and the EGIDE scholarship for financial support. The present work was also partially supported by the Labex ARCANE (
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