Microbial Fuel Cells
An Organic Way of Energy
A biosensor is a device that uses a living organism or biological molecules, especially enzymes or antibodies, to detect the presence of chemicals.
A biosensor is a device that uses a living organism or biological molecules, especially enzymes or antibodies, to detect the presence of chemicals.
BIOSENSOR
HOW MFCs ARE USED AS BIOSENSORS
The electrical current generated from a microbial fuel cell is proportional to the energy content of wastewater used as fuel. An MFC can be defined as a biosensor system because it is used to measure the solute concentration of wastewater (1). Biochemical oxygen demand (BOD) are values of the strength of wastewater meaning, the amount of dissolved oxygen needed by the microbial fuel cells to break down organic material in the solution (2).
In the video to the left is an more in depth explaination of what a biosensor is, by explaining the components of a biosensor (5.2)
Advantages of MFC Biosensors
In the fabrication of biosensors, enzymes are the most widely used biological sensing element. Because of tedious, time consuming and costly enzyme purification, purified enzymes in the application in biosensor construction is not ideal. A normal biosensor has a requirement of multiple enzymes to generate the measurable product of the cofactor/coenzyme while microorganisms(MFCs) provide an ideal alternative.Because many enzymes and co-factors that co-exist in the cell give the cells the ability to consume, allowing them to detect lar amount of chemicals, however this can compromise the selectivity. Microbial Fuel Cell can be easily manipulated and adapted to consume/degrade new substrate under the cultivating condition. And because of the the progress in recombinant DNA technologies, it has opened endless possibilities of manipulating the microorganisms to improve the activity of an enzyme, making microbes an excellent biosensing element.(3)
Examples of MFC Biosensors
Amperometric Microbial Biosensor
Amperometric microbial biosensor operates at fixed potential with a reference electrode and involves the detection of the current generated from the oxidation of species at the surface of the electrode. Amperometric microbial biosensors have been widely developed for the determination of biochemical oxygen demand for the measurement of biodegradable organic pollutants in aqueous samples. (3)
Colorimetric Biosensor
The colorimetric biosensor is sensitive based on color changes in the toxin sensitive colored living cells. In the presence of toxins produced by microbial pathogens, the cells undergo a color change. This color change, changes in a dose dependant manner. The results suggest the cell-based biosensor’s potential application in the detection and identification of virulence activity is associated with certain air, food, and water-borne bacterial pathogens. (3)
Conductimetric Biosensor
This biosensor contains a microbe-catalyzed reaction which involves a change in ionic species. This is associated with a net change in the conductivity of the reaction solution. Even though the detection of the solution conductance is non-specific, conductance measurements are extremely sensitive. A single use of conductivity and microbial sensor was developed to investigate the effect of both species and concentration of the anions on the metabolic activity of E. coli. This hybrid sensing system combines physico-chemical and biological sensing and greatly increases the ease with which comparative data can be assimilated. (3)
Potentiometric Microbial Biosensor
Potentiometric microbial biosensors consist of an ion-selective electrode or a gas-sensing electrode that is coated with an immobilized microbe layer. The microbe consuming analyte generates a change in potential as a result from the ion accumulation/depletion. Potentiometric transducers measure the difference between a working electrode and a reference electrode, and the signal is correlated to the concentration of the analyte. Due to a logarithmic relationship between the potential generated and analyte concentration, a wide detection range is possible. However, this method requires a very stable reference electrode, which is a limitation of the transducers. (3)