Examining the resistance and resilience of anode-respiring Shewanella oneidensis biohybrid using microsensors.

Immobilizing electro-active microbes within polymer matrices (thereby forming biohybrids) is a promising approach to accelerate microbial attachment to electrodes and increase the biofilm robustness. However, little is known on the fine scale chemical environment that develops within the electro-active biohybrids. Herein, we develop a biohybrid by immobilizing a culture of Shewanella oneidensis MR1 in agar matrix on the surface of a graphite electrode poised at +0.25 V. The resulting bioanode (3-6 mm thick) was grown under anoxic conditions and produced a steady current of 40 µA. Oxygen and pH distribution within the biohybrid were characterized in-situ using microsensors. As Shewanella is a facultative aerobe, it will halt the current production in the presence of oxygen. Thus, in addition, we investigated the alteration of the microenvironment during and after aeration of the medium to evaluate the oxygen tolerance of the system. During aeration, oxygen was effectively consumed in the top layers of the biofilm, leaving a 400-900 µm thick anoxic zone on the anode surface, that sustained >60% of the initial current. Current production recovered to pre-oxic condition within 5 h after the aeration was stopped, showing that immobilization can promote both high resistance and resilience of the system. Despite the absence of strong buffering conditions, pH profiles indicated a maximum drop of 0.2 units across the biohybrid. Characterizing the chemical microenvironment helps to elucidate the mechanistic functioning of artificial biofilms and hold a great potential for the designing of future, more effective biohybrid electrodes.

A flexible and disposable battery powered by bacteria using eyeliner coated paper electrodes.

Herein, an environment friendly paper-based biobattery is demonstrated that yields a power of 12.5W/m3. Whatman filter papers were used not only as support for electrode fabrication but also as separator of the biobattery. To provide electrical conductivity to the paper-based cathode and anode, commercially available eyeliner containing carbon nanoparticles and Fe3O4 was directly employed as conductive ink without any binder. With an instant start-up, the as-fabricated biocompatible electrodes could hold bacteria in an active form at the anode allowing chemical oxidation of organic fuel producing current. The facile process delineated here can be employed for the tailored electrode fabrication of various flexible energy harnessing devices.

Instant power generation from an air-breathing paper and pencil based bacterial bio-fuel cell.

We present a low-cost, disposable microbial fuel cell fabricated on a paper based platform, having a start-up time of 10 s. The platform deploys ordinary pencil strokes for graphite electrode deposition. The device uses a membrane-less design in a one-time injection (OTI) mode or a continuous capillary driven flow mode (CPF), where oxygen from the atmosphere is used up at the cathode for water formation, leading to the generation of bioelectricity. The performance of the fuel cell is evaluated using two bacterial strains, namely, Pseudomonas aeruginosa IIT BT SS1 and Shewanella putrefaciens. This flexible device is shown to retain bacteria for a period of at least one hour, resulting in the generation of almost 0.4 V using P. aeruginosa and a maximum current of 18 µA using S. putrefaciens without the use of any additional catalysts.