Nano-Assembled Enzymatic Bioanodes and Its Application toirect Glucose Fuel Cells

In this study, we developed a highly stable and biocompatible bioanode based on biomaterials with a simple, fast and cost-effective process, and enhanced we its catalytic activity for glucose by carbon nanotubes (CNT). In our research, glucose oxidase (GOx) and laccase were chosen as biocatalysts for the oxidation of glucose and the reduction of oxygen, respectively, in biofuel cells. The chosen mediators for the bioanodes were 1,4-benzoquinone or 2,5-dihydroxybenzaldehyde (DHB) depending on the immobilizing methods, and ABTS was the mediator for cathode. To develop a reliable enzymatic biofuel cell, we prepared enzymatic electrodes by adsorption method first, which is an easier and faster way. A biofuel cell assembled by such a bioelectrode can generate energy with a maximum power density of ca. 16 μW/cm2 for a two- compartment system, and ca. 9 μW/cm2 for a membraneless system. However, there is a serious leaching problem of enzymes and mediators, and it caused the unstability of bioelectrodes. A highly stable nano-assembled bioanode, SPCE/CNT/BSA-GOx-DHB, was developed by covalent immobilization of GOx and DHB with a cross-linked bovine serum albumin matrix. The bioanode showed reversible redox activity of DHB, and the amount of immobilized DHB on the electrode was evaluated ca. 3.82×10-9 mole/cm2. The catalytic response of glucose increased more than 100 times when we modified the bioanode with CNT, and it’s further improved by optimizing the crosslinking process. In flow inject mode, the bioanode showed steady and reproducible responses to glucose oxidation under continuous detection. The KM of bioanode was determined to be 130.1 ± 23.60 mM, which indicates that the activity of glucose oxidase is kept after crosslinking. And the bioanode also showed high storage stability, where more than 85% of activity after storage in PBS solution for 7 days. To construct the glucose/O2 biofuel cell, we assembled the SPCE/CNT/BSA-GOx-DHB anode with a laccase solution cathode. The cell’s open circuit voltage was 0.68 V and its maximum power density was 16.13 μW/cm2 at 0.2 V in pH 7 PBS at 25 ℃ with 100 mM glucose. CNT and gold nanoparticles (Au-NP) were added in the crosslinking mixture, respectively, to improve the conductivity, and it increased 10 % of the maximum power density.