Enzymatic Biofuel Cell with Self-regulating Enzyme-Nanotube Ensemble Films
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Enzymatic Biofuel Cell with Self-regulating Enzyme-Nanotube Ensemble Films TAKEO MIYAKE1,2, SYUHEI YOSHINO1, TAKEO YAMADA2,3, KENJI HATA2,3, MATSUHIKO NISHIZAWA1, 2 1
Department of Bioengineering and Robotics, Graduate school of Engineering,Tohoku University,
6-6-1 Aramaki Aoba, Aoba-ku, Sendai 980-8579, Japan. 2
JST-CREST, Sanbancho, Chiyodaku, Tokyo, 102-0075, Japan
3
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 5,
1-1-1 Higashi, Tsukuba, Ibaraki 308-8565, Japan.
ABSTRACT Nanostructured carbons have been widely used for fabricating enzyme-modified electrodes due to their large specific surface area. However, because they are random aggregates of particular or tubular nanocarbons, the post-modification of enzymes to their intra-nanospace is generally hard to control. Here, we describe a free-standing film of carbon nanotube forest (CNTF) that can form a hybrid ensemble with enzymes through liquid-induced shrinkage. This provides in-situ regulation of its intra-nanospace (inter CNT pitch) to the size of enzymes, and eventually serves as a highly active electrode. The CNTF ensemble with fructose dehydrogenase (FDH) showed the oxidation current density of 16 mA cm-2 in stirred 200 mM fructose solution. The power density of a biofuel cell using the FDH-CNTF anode and the Laccase-CNTF cathode reached 1.8 mW cm-2 (at 0.45 V) in the stirred oxygenic fructose solution, more than 80 % of which could be maintained after continuous operation for 24 h. Application of the free-standing, flexible character of the enzyme-CNTF ensemble electrodes is demonstrated via their use in the patch or wound form.
INTRODUCTION Enzyme-modified electrodes are core components of bioelectronic devices such as biofuel cells, which have attracted attention as safe power sources, generating electricity from natural fuels like sugars and alcohols [1,2]. A variety of nanoengineered carbon electrodes for biofuel cells have recently been developed in rapid succession [3,4]. However, all attempts to incorporate nanoengineered carbon electrodes have focused on pre-structuring electrodes before enzyme modification. This is because the process for engineering carbon is bio-incompatible due to the use of organic solvents or heating. If the nanostructure of the electrode can be regulated in response to the enzyme to be immobilized, the resultant enzymatic ensemble would avoid the difficulty in post-modification of enzymes. We present here a method to achieve ideal enzyme electrodes having suitable intra-nanospace automatically regulated to the size of enzymes [5]. We utilize a carbon nanotube forest (CNTF) consisting of extremely long (~1 mm) single-walled CNTs [6], which can be
handled with tweezers, as a 100% binder-free carbon film. When liquids are introduced into the as-grown CNTF (CNTs with a pitch of 16 nm) and dried, the CNTF shrinks to a near-hexagonal close-packed structure (CNTs with a pitch of 3.7 nm) because of the surface tension of the liquids [7,8]. By using an enzyme solution as the liqui
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