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3-Dimensional, Enzyme Biohydrogel Electrode for Improved Bioelectrocatalysis Ananta Ghimire, Ajith Pattammattel, Charles Maher, Rajeswari Kasi, and Challa V. Kumar ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b13606 • Publication Date (Web): 15 Nov 2017 Downloaded from http://pubs.acs.org on November 16, 2017
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ACS Applied Materials & Interfaces
3-Dimensional, Enzyme Biohydrogel Electrode for Improved Bioelectrocatalysis
Ananta Ghimirea, Ajith Pattammattela, Charles E. Mahera, Rajeswari M. Kasia,b*, Challa V. Kumara,b,c*
aDepartment bPolymer
of Chemistry, University of Connecticut Storrs, CT 06269-3060
Program, Institute of Materials Science, U-3136, University of Connecticut Storrs, CT 06269
cDepartment
of Molecular and Cellular Biology, University of Connecticut Storrs, CT 06269 *
[email protected], *
[email protected] 860-486-3213 (phone) 860-486-2981 (fax)
KEYWORDS: Mobile mediators, bioelectrocatalysis, high current density, protein network, EDC coupling, glucose oxidase, carbon cloth, biofuel cell
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ABSTRACT Higher loading of enzymes on electrode and efficient electron transfer from the enzyme to the electrode are urgently needed to enhance the current density of biofuel cells. The two-dimensional nature of electrode surface limits the enzyme loading on the surface and unfavorable interaction with electrode surfaces cause inactivation of the enzyme. Benign biohydrogels are designed here to address enzyme degradation and the three-dimensional nature of the biohydrogel enhanced the enzyme density per unit area. A general strategy is demonstrated here using a redox active enzyme glucose oxidase (GOx) embedded in bovine serum albumin (BSA) biohydrogel on flexible carbon cloth (CC) electrodes. In presence of ferricyanide as mediator, this bioelectrode generated a maximum current density (jmax) of 13.2 mA.cm-2 at 0.45 V in the presence of glucose with a sensitivity of 67 μA.mol-1.cm-2 and a half-life of >2 weeks at room temperature. Strong correlation of current density with water uptake by the biohydrogel was observed. Moreover, a soluble mediator (sodium ferricyanide) in the biohydrogel enhanced the current density by ~1000 folds and citrate-phosphate buffer has been found to be the best to achieve the maximum current density. A record 2.2% of the loaded enzyme was electroactive, which is greater than the highest value reported (2 folds)1,2,3,4,5. Stabilization of the enzyme in the biohydrogel resulted in retention of the enzymatic activity over a wide range of pH (4.0-8.0). We showed here that biohydrogels are an excellent
media
for enzymatic electron
transfer reactions
required for
bioelectronics and biofuel cell applications.
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ACS Applied Materials & Interfaces
1.0 Introduction A novel method to interlock bovine serum albumin (BSA) and glucose oxidase (GOx) with water-soluble amino acids (Xaa) using carbodiimide (EDC) chemistry to form a highly electroactive enzyme network around the fibers of carbon cloth is reported here. This method helps overcome three major challenges (i) increasing the loading of electroactive GOx species (ii) increasing the percent GOx electroactive and (iii) increasing the stability of GOx. This BSA-GOx-Arg (Arginine, Arg) coated on carbon cloth anode presents enhanced current densities and increase in percentage of electroactive GOx species when compared to other state-of-the-art bio-electrodes.1,2,3,4,5 This glucose oxidase modified carbon cloth may serve as an anode for sugar-to-power conversion in biofuel cells (BFC). The power output of bioelectrodes depends on the fraction of redox active enzyme on the electrode, its activity, stability and its electrical contact with the electrode. Maximizing the loading of electroactive enzyme on the electrode is challenging because of spontaneous enzyme denaturation on the electrode surface. Several different methods have been developed to improve loading of electroactive enzymes and prevent leaching of the enzyme from the electrode surface. This includes the use of (i) entrapping enzymes within polymer like nafion2,5 and cellulose,1 (ii) covalent immobilization of enzyme onto the functionalized carbon electrode6 and (iii) formation of 3D network of enzymes on the electrode surface7,8,9. The first two methods have been extensively used in sensing while the third method enhanced loading of the enzyme10 for BFC applications, which is the focus of this work.
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Recently, 3D networks with high water content have gained much attention as electrode materials.11,12,25 Compared to other enzyme immobilization techniques, formation of 3D network on the electrode surface not only improves enzyme loading per unit area of the electrode surface, but also protects the enzyme from denaturation by maintaining a crosslinked hydrophilic environment. These crosslinked enzyme networks are often derived from synthetic polymers, carbohydrates 13 , proteins 14 , DNA13, 15 and other water soluble or dispersible systems. These 3D networks on modified electrodes are generally synthesized by (i) drop casting or physical adsorption of the network onto the electrode surface13,16,17, (ii) chemical crosslinking with functionalized electrode surface 18 and (iii) entrapping the network using polymers, like chitosan17. These methods enhanced enzyme loading but electro-active enzymes is still very low (50 mg/mL) were stable and showed
