Electrochemical methods for generation of a biological proton motive force and pyridine nucleotide cofactor regeneration

Abstract

Disclosed are methods using neutral red to mediate the interconversion of chemical and electrical energy. Electrically reduced neutral red has been found to promote cell growth and formation of reduced products by reversibly increasing the ratio of the reduced:oxidized forms of NAD(H) or NADP(H). Electrically reduced neutral red is able to serve as the sole source of reducing power for microbial cell growth. Neutral red is also able to promote conversion of chemical energy to electrical energy by facilitating the transfer of electrons from microbial reducing power to a fuel cell cathode.

We claim:  
     
         1 . A method for generating electricity using a biological system comprising the steps of: 
 (a) providing an electrochemical fuel cell system comprising an anode compartment and a cathode compartment separated by a cation-selective membrane, wherein each compartment is equipped with an electrode, wherein the electrodes are connected by a wire to a multimeter;    (b) placing an anolyte in the anode compartment, the anolyte comprising a suitable concentration of neutral red and a biological catalyst selected from the group consisting of resting cells, growing cells, and anaerobic sludge comprising cells, or a combination thereof;    (c) placing a suitable catholyte in the cathode compartment; and    (d) allowing the neutral red-mediated conversion of chemical reducing power to electricity.    
     
     
         2 . The method of  claim 1 , wherein the biological catalyst comprises photosynthetic bacteria.  
     
     
         3 . The method of  claim 1 , wherein the biological catalyst comprises lithotrophic bacteria.  
     
     
         4 . The method of  claim 1 , wherein the biological catalyst comprises organotrophic cells.  
     
     
         5 . The method of  claim 1 , further comprising the step of supplementing the anolyte with an energy source that can be used by the biological catalyst.  
     
     
         6 . The method of  claim 1 , wherein the energy source comprises light, organic compounds, or molecular hydrogen (H 2 ).  
     
     
         7 . A method for detecting the presence of a specific organic or inorganic test compound in a sample comprising: 
 (a) providing biosensor comprising an electrochemical fuel cell system having an anode compartment and a cathode compartment separated by a cation-selective membrane, wherein each compartment is equipped with an electrode, wherein the electrodes are connected by a wire to a multimeter;    (b) placing an anolyte in the anode compartment, the anolyte comprising the sample, a suitable concentration of neutral red, and a biological catalyst selected from the group consisting of whole cells and an enzyme, wherein the biological catalyst is able to oxidize the test compound;    (c) placing a suitable catholyte in the cathode compartment;    (d) allowing oxidation of at least a portion of any test compound present in the sample and reduction of at least a portion of oxidized neutral red;    (e) allowing the transfer of electrons from reduced neutral red to the cathode; and    (f) detecting the generation of an electrical current.    
     
     
         8 . The method of  claim 7 , further comprising the step of determining the concentration of the test compound in the sample.  
     
     
         9 . A method for measuring the chemical oxygen demand in waste water comprising the steps of: 
 (a) providing an electrochemical fuel cell system comprising an anode compartment and a cathode compartment separated by a cation-selective membrane, wherein each compartment is equipped with an electrode, wherein the electrodes are connected by a wire to a multimeter;    (b) placing an anolyte in the anode compartment, the anolyte comprising a suitable concentration of neutral red and waste water comprising or supplemented with a biological catalyst;    (c) placing a suitable catholyte in the cathode compartment;    (d) allowing the neutral red-mediated conversion of chemical reducing power to electricity; and    (e) measuring the electrical current generated by the fuel cell system.