Preparation of Chitosan-Based Enzyme Inks for Paper-Based Screen-Printed Biofuel Cells
Authors: Oda Kanako , Yoshihara Yuko , Hoshi Yoshinao , Watanabe Hikari , Shitanda Isao , Abdelkader Zebda , Mikawa Tsutomu , Tsujimura Seiya , Itagaki Masayuki 
Published: December 2020

We have developed paper-based screen-printed biofuel cells using MgO-templated carbon (MgOC) as an electrode material1) in which a mediator and an enzyme were immobilized by dropping the solutions on the MgOC surface. However, the immobilization scheme should be shortened for practical applications. In this study, we newly prepare an enzyme-modified carbon ink using chitosan, which has high bio-affinity as a binder. By preparing chitosan-based enzyme ink, it becomes possible to immobilize the enzyme on the electrode by a simple printing process. A paper-based glucose/O2 biofuel cell was fabricated by screen printing with the enzyme-modified carbon inks. In this abstract, we describe the results of the glucose anode.
Firstly, a glucose oxidase (GOx) and 1,2-naphthoquinone (1,2-NQ) were physically adsorbed in the pores of the MgOC. Then a chitosan-based enzyme ink was prepared by mixing the GOD and 1,2-NQ immobilized MgOCwith chitosan, and then cross-linked with genipin. A commercially available carbon ink and the as-prepared chitosan-based enzyme ink were successively printed on a water-repellent Japanese paper and dried overnight in a refrigerator to prepare a bioanode. In this study, we used two kinds of carbon. One is an untreated MgOC (normal MgOC). Another is a “washed MgOC”, which were washed with 0.25M NaOH and pure water before the chitosan-based enzyme ink was prepared.
Anodes prepared with chitosan-based enzyme inks using normal MgOC and washed MgOC were evaluated by chronoamperometry (measurement potential: 0.2 V) in phosphate buffer containing 100 mM glucose (Fig.1 (a)).
The catalytic oxidation reaction was not observed in the anode using normal MgOC, whereas the catalytic oxidation current of about 0.5 mA/cm2 was obtained after 500 seconds in the anode using the washed MgOC. From the SEM (accelerating voltage: 15.0 kV) of the anode using washed MgOC, a structure with many macroporesof about 5 to 10 µm was observed clearly. (Fig. 1(b)). On the other hand, no such macropores were observed in the anode using normal MgOC.
The surface of normal MgOC has many functional groups such as -COOH, and it shows acidity when mixed with water. The cross-linking reaction does not occur sufficiently in between genipin and chitosan under acidic condition. On the other hand, in the neutral condiiton, the cross-linking reaction that accompanies the self-polymerization of genipin proceeds enough to form long and flexible chains 2). Therefore, the neutralization of the MgOC surface by the washing treatment forms an electrode with macropores between carbons, resulting in increase of glucose supply to the GOD immobilized in the mesopore of MgOC.

References

1) Isao Shitanda et al., J. Electrochem. Soc, 166(12) (2019) B1063-B1068.
2) Elí Emanuel Esparza Floreset et al., Process Biochemistry, 84, (2019) 73-80.

Acknowledgements

This work was partially supported by JST-ASTEP Grant Number JPMJTS1513, JSPS Grant Number 17H02162 and Private University Research Branding Project (2017-2019) from Ministry of Education, Culture, Sports, Science and Technology, and Tokyo University of Science Grant for President's Research Promotion．

Figure 1