Polymers Based on Sulfonated Polyanillines for Direct Electron Transfer with (PQQ)GDH and Application in Carbon Nanostructure-Based Biofuel Cells

Dopant-functionalized anilines with improved electrocatalytic properties are promising building blocks for the construction of bioelectronic devices [1]. The present study is devoted to the use of polyanillines possessing different substitution patterns in the interaction with the enzyme PQQ-GDH (pyrroloquinoline quinone dependent glucose dehydrogenase). The aim is to obtain an electron transfer from the substrate reduced enzyme to the polymer without additional shuttle molecules. This has been first studied in solution and then transferred to a surface in order to build a reagentless enzyme electrode.

6 polymers have been prepared from different mixtures of sulfoxy-, methoxy- and carboxy-substituted aniline by chemical synthesis and characterized by UV/VIS, IR and NMR spectroscopy. The substitution pattern influences the reactivity of the different polymers with the enzyme in solution, however when fixed on electrode surfaces the potential can be effectively used to enforce the reaction [2].

One of the polymers (poly(3-aminobenzoic acid-co-2-methoxyaniline-5-sulfonic acid) has been applied in modifying carbon nanotube based electrode structures and coupling (PQQ)GDH for construction of a bioanode. The first fuel cell uses MWCNT-based bucky paper as electrode material. The PQQ-GDH has been covalently coupled to the polymer. The glucose oxidation of this electrode achieves a current density of 700μA/cm². As cathode PQQ modified bucky paper with covalently bound BOD (bilirubin oxidase) is applied. For this electrode a start potential of about 0.5V vs. Ag/AgCl and a maximum current density of 1mA/cm² can be observed. The biofuel cell resulting from the bucky paper electrodes shows current densities up to about 100μW/cm² in a 10mM glucose solution.

In a second approach vertically aligned carbon nanotubes (vaCNT) have been used for the electrode construction. Both enzymes have been immobilized in a similar way as compared to bucky paper. The vaCNT-based fuel cell achieves a maximum power density of 125µW/cm². Even after three days and several runs of load a power density of more than 110µW/cm² is retained (quiescent solution, 10mM glucose, room temperature). Furthermore it can be shown that this biofuel cell operates in human serum samples.

[1] Wallace GG, Kane-Maguire LAP. Manipulating and monitoring biomolecular interactions with conducting electroactive polymers. Adv Mater 511 2002;14:953–60.

[2] Sarauli D et al. Differently substituted sulfonated polyanilines: The role of polymer compositions in electron transfer with pyrroloquinoline quinone-dependent glucose dehydrogenase Acta Biomater 2013; 9: 8290-8298