Electrochemical biosensor for aerobic acetate detection

There is an increasing demand on alternatives methods to animal testing. Numerous health parameters have been already studied using in vitro devices able to mimic the essential functions of the organs, being the real-time monitoring and response to stimuli their main limitations. Regarding the health of the gut, the short chain fatty acids, and particularly acetate, have emerged as key biomarkers to evaluate gut healthiness and disease development, although the number of acetate biosensors is still very low. This article presents a microbial biosensor based on fully biocompatible materials which is able to detect acetate in aerobic conditions in the range between 11 and 50 mM, and without compromising the viability and function of either bacteria (>90% viability) or mammalian cells (>80% viability). The detection mechanism is based on the metabolism of acetate by Escherichia coli bacteria immobilized on the transducer surface. Ferricyanide is used as a redox mediator to transfer electrons from the acetate metabolism in the bacterial cells to the transducer. High bacterial concentrations are immobilized in the transducer surface (109 cfu mL-1) by electrodeposition of conductive alginate hydrogels doped with reduced graphene oxide. The results show successful outcomes to exploit bacteria as a biosensing tool, based on the use of inkjet printed transducers, biocompatible materials and cell entrapment technologies.

Scratching and transplanting of electro-active biofilm in fruit peeling leachate by ultrasound: re-inoculation in new microbial fuel cell for enhancement of bio-energy production and organic matter detection

OBJECTIVE

An electro-active biofilm of Fruit Peeling (FP) leachate was formed onto the Carbon Felt (CF) bio-anode in a Microbial Fuel Cell (MFC), after functioning for a long time. The electro active-biofilm thus formed was then scratched by ultrasound and re-inoculated in a new leachate to be transplanted onto the bio-anode. This procedure allowed the microbial electron charge transfer and therefore the enhancement of the bio-energy production of the fuel cell.

RESULTS

By using the repetitive mechanical biofilm removal, re-suspension and electrochemically facilitated biofilm formation, the voltage was substantially increased. In effect, the voltage of the 1st G of biofilm, rose gradually and reached its maximum value of 65 mV after 10 days. Whilst the 2nd generation allowed to obtain the maximum voltage 276 mV and without any lag time. The DCO abatement using the 1st G biofilm was 68% greater than the 3rd G 26%. Besides, the electrochemical impedance spectroscopy characterization and cyclic voltammetry of bio-anode with 2nd G biofilm confirmed the ability of electro-active biofilm formation on a new support. The biofilm transplanted showed thus greater kinetic performance, with reduced lag time demonstrating the interest of the selection that took place during the formation of successive biofilms.

CONCLUSIONS

Despite the transplantation of the electro-active biofilm onto the bio-anode, the MFC still produced relatively lower power output. Nevertheless, it has been tested successfully for monitoring and detecting the oxidation of sodium acetate substrate in the very wide concentration range 0.0025-35 g/l.