Bacterial-biofilm enhanced design for improved electrocatalytic reduction of oxygen in neutral medium Weronika A. Lotowska a,c , Iwona A. Rutkowska a , Ewelina Seta a,c , Ewelina Szaniawska a , Anna Wadas a , Slawomir Sek a,c , Adrianna Raczkowska b , Katarzyna Brzostek b , Pawel J. Kulesza a,c, * a University of Warsaw, Faculty of Chemistry, Pasteura 1, PL-02-093 Warsaw, Poland b University of Warsaw, Faculty of Biology, Miecznikowa 1, PL-02-096 Warsaw, Poland c Biological and Chemical Research Center, University of Warsaw, Zwirki i Wigury 101, PL-02-096 Warsaw, Poland A R T I C L E I N F O Article history: Received 4 March 2016 Received in revised form 18 July 2016 Accepted 20 July 2016 Available online 21 July 2016 Keywords: Yersinia enterocolitica bacterial biofilm Multi-walled carbon nanotubes Co-porphyrin Oxygen and hydrogen peroxide reductions Pt nanoparticles A B S T R A C T The specific reactivity and ability of biofilms to form stable polymer-like hydrogel aggregates of microorganisms adhering to common solid (including the glassy carbon electrode) surfaces have been explored here to form systems analogous to electrocatalytic redox-polymer modified electrodes. Growth of biofilms has been demonstrated with use of Yersinia enterocolitica, a robust Gram-negative rod-shaped bacteria known to be resistive to pH changes (4-10) and temperature variations (0–40  C). Charge distribution and propagation within the biofilm have been enhanced by introduction of multi-walled carbon nanotubes. The fact that carbon nanotubes are derivatized with the carboxyl-group containing 4- (pyrrole-l-yl) benzoic acid has facilitated the hybrid material integrity and stability, namely through electrostatic attractive interactions between anionic carboxyl sites and positively charged domains of bacterial aggregates. In neutral media, the biofilm-based composite (hybrid) matrices have exhibited themselves electrocatalytic activity during electroreductions of oxygen and hydrogen peroxide (with possibility of its sensing in a broad range of concentrations). By immobilizing additional catalytic (cobalt porphyrin) sites, a truly bifunctional redox-polymer-like electrocatalytic system capable of significantly enhancing oxygen reduction currents has been produced. Apparently, the reduction of oxygen (to hydrogen peroxide) is initiated at cobalt porphyrin centers, and the second step (decomposition of hydrogen peroxide intermediate to water) is pursued at reactive sites (perhaps c-cytochrome) existing within biofilm matrix. Comparative measurements have been performed with the biofilm-supported platinum nanoparticles as well as with such a model catalytic system as platinized carbon nanotubes. The proposed electrode designs are relevant to biosensing and to the development of alternate cathode materials for biofuel cells or biobatteries. ã 2016 Elsevier Ltd. All rights reserved. 1. Introduction There has been growing interest in fabrication of electro- catalytic systems for oxygen and hydrogen peroxide reductions that would be useful in biological media, i.e. neutral solutions. While stable bioelectrocatalytic systems for efficient (four-electron and preferably with low-overpotential) oxygen reduction are of importance to such technologies as biofuel cells and biobatteries, the well-behaved catalytic electrodes for accurate and reliable voltammetric or amperometric detection and determination of hydrogen peroxide are of interest to the development of both biomedical and environmental sensors. Oxygen biocathodes utilizing fungal laccases or bilirubin oxidases are highly specific and often perform better at ambient temperatures than noble metal (e.g. platinum) based catalysts for the oxygen electroreduction in neutral media. The enzymes belong to a group of proteins with the copper active centers, and they can lower the oxygen reduction reaction overpotential both in the absence [1,2] and presence of mediators [3]. Despite significant progress in their practical utilization, high cost and the complex proteic structure of those enzymes often result in lack of stability and poor reproducibility of operation [4]. * Corresponding author at: University of Warsaw, Faculty of Chemistry, Pasteura 1, Warsaw PL-02-093, Poland. Tel.: +48 22 5526211; fax: +48 22 5526434. E-mail address: pkulesza@chem.uw.edu.pl (P.J. Kulesza). http://dx.doi.org/10.1016/j.electacta.2016.07.117 0013-4686/ã 2016 Elsevier Ltd. All rights reserved. Electrochimica Acta 213 (2016) 314–323 Contents lists available at ScienceDirect Electrochimica Acta journal homepa ge: www.elsev ier.com/locate/electacta