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Figure 1: Cyclic Voltammetry comparing a glassy carbon electrode with one that was functionalized with NR. The substrate bears two nitrogroups so two reductive waves are observed. These are strongly enhanced by the presence of the enzyme, that accelerates electron transfer from the compound to the electrode. The test compound was dinitrotoluene, a model for the insecticide and fungicide dinoseb.
 

Figure 2: Depiction of Layer-by-Layer entanglement of laccase within pores of PVDF membrane, resuling in conversion of vanillyl alcohol to vanillin as solution passes through the membrane. LbL immobilization involves initial deposition of negatively charged PAA (polyacrylic acid) then positively charged PAH (blue, polyallylamine hydrochloride) and laccase. The exposed Lys side chains of laccase are attracted to negatively charged PAA and adhere to it to become entangled in PAH that also adheres to PAA.
 

Figure 3: Cartoon of experiment in which an electrode that has been functionalized with lumiflavin evolves O2 and demonstrates the associated photocurrent (lower inset), whereas bare glassy C electrode does neither. Upper inset: Illumination of flavin-functionalized electrode in water.

Smart Devices for a Cleaner Leaner World: Membranes and Elelectrodes functionalized with Enzymes and Cofactors. 
 

Nitroreductase in Bioremediation.

Nitroreductase (NR) is able to transform diverse nitrated aromatics and quinone-related compounds. This makes it a useful tool for remediation of polluting dyes, herbicides, pesticides, antibiotics and even high explosives (TNT) [22]. High school students in our lab have immobilized NR on inexpensive graphite and glassy carbon electrodes, and documented accelerated conversion of various xenobiotics (Figure 1). Thus, enzyme functionalized electrodes can serve as electrical sensors of such compounds and means to remediate them. We are working to produce NR-functionalized membranes which will transform dissolved nitroaromatics as a solution passes through, providing a continuous flow system for efficient one-pass decontamination.

Enzyme-functionalized Membranes for value-added conversions.

We are employing the layer-by-layer technology to immobilize NR on membranes, as this method not only enables recharging of the membranes with fresh enzyme, but also extends the life time of bound enzymes due to their isolation and entanglement in stabilizing matrix [89]. Such membranes have been used successfully to transform lignin waste streams and conversion a monomer found in lignin waste streams to the value-added food additive vanillin.

Photostimulated Electrochemistry of the Simplest Flavoenzyme: A Flavin.

Flavins strongly absorb visible light forming a photoexcited state that is a strong oxidant due to the hole in the HOMO as well as a strong reductant due to the excited electron in the LUMO. Indeed we showed that lumiflavin immobilized on glassy carbon electrodes acts as a photosensitiser extracting electrons from water and passing a catalytic current to the electrode (Figure 3) [84]. The slow increase in the photocurrent indicates slow but reversible formation of a species with higher water oxidizing activity than lumiflavin itself. Most water-oxidizing catalysts to date have been inorganic complexes. These pose a pollution risk and can be costly to generate and properly dispose of. In contrast, flavins are composed of only H, C, O and N, and can be synthesized in modified forms to tune the reactivity and optimize the electrode for desired chemistry. Their ability to capture energy from light also enables them to minimize the energy cost of water oxidation and paves the way for photoelectrocatalytic mediation and other reactions as well.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Updated: Oct. 2017                                                                                               

Copyright 2017 A.-F. Miller     

Comments: A.-F. Miller