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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

Carbon nanotubes (CNTs) arranged in 3 dimensional structures represent an interesting material for the development of biocatalytic electrodes. Due to their architecture they can provide docking places for enzymes and after modification of the surface properties often a direct electrochemistry can be observed. The direct electron transfer where the catalytic starts near the E0 of the enzymes redox center can avoid a loss of in cell potential and allows the development of efficient enzymatic biofuel cells (EBFC). Also the membrane-less construction of the EBFCs is advantageous for high power output. With this respect the pyrroloquinoline quinone dependent glucose dehydrogenase ((PQQ) GDH) is an interesting enzyme since it is insensitive towards oxygen which is the terminal electron acceptor at the cathode. Here two types of carbon nanotubes materials - bucky paper (BP) and vertically aligned carbon nanotubes (vaCNTs) - are used for the development of glucose/oxygen biofuel cells. For the anode development these materials are modified with poly(3-aminobenzoic acid-co-2-methoxyaniline-5-sulfonic) acid (PABMSA) for covalent coupling of the glucose oxidizing (PQQ) GDH. The cathode is based on the oxygen reducing Bilirubin oxidase (BOD) which is covalently coupled to PQQ modified BP and vaCNTs electrodes. For the electrochemical characterisation of the individual electrodes voltammetric measurements are performed. The voltammograms for the different anode preparations show that the modification of both carbon nanotube materials with an aniline-based polymer film (PABMSA) and covalent enzyme coupling result in an direct enzyme-electrode contact. The influence of the polymer concentration during the electrode preparation and the impact of the buffer composition on the current density are investigated. Both electrode materials show the highest current density in 100 mM citrate phosphate (CiP) buffer containing 10 mM glucose and applying 5 mg/ml PABMSA for CNTs modification. For the BP-based anode current densities up to 0.75 mA/cm2 can be detected while electrodes made of vaCNTs reveal a maximum current density of 1.3 mA/cm2 at +0.1 V vs. Ag/AgCl. The cathode construction with PQQ as interlayer and a covalent attachment of the BOD to the carboxylic groups shows the highest electrocatalytic activity under air saturated conditions – for bucky paper about 1 mA/cm2 at 0.1 V vs. Ag/AgCl. Applying vaCNTs for the BOD-cathode development a local maximum current of 1.3 mA/cm2 and a steady-state catalytic current of 0.55 mA/cm2 at +0.1 V vs. Ag/AgCl can be obtained. A combination of the BP-based  (PQQ)GDH/PABMSA and BOD/PQQ electrodes in a biofuel cell application achieves a power output of 107 µW/cm2 at a cell potential of 490 mV. The same modification procedures and enzymes applied in a vaCNTs fuel cell lead to a power density of 122 µW/cm2 at cell potential of 540 mV. The separate evaluation of both carbon nanotubes based materials reveal a better stability of the vaCNTs-based enzyme electrodes.