A new enzyme catalyst consisting of pyrenecarboxaldehyde (PCA) and glucose oxidase (GOx) immobilized on polyethyleneimine (PEI) and a carbon nanotube supporter (CNT/PEI/[PCA/GOx]) is suggested, and the performance and stability of an enzymatic biofuel cell (EBC) using the new catalyst are evaluated. Using PCA, the amount of immobilized GOx increases (3.3 U mg − 1 ) and the electron transfer rate constant of the CNT/PEI/[PCA/GOx] is promoted (11.51 s − 1 ). Also, the catalyst induces excellent EBC performance (maximum power density (MPD) of 2.1 mW cm − 2 ), long-lasting stability (maintenance of 93% of the initial MPD after 4 weeks) and superior catalytic activity (flavin adenine dinucleotide redox reaction rate of 0.62 mA cm − 2 and Michaelis-Menten constant of 0.99 mM). These characteristics are ascribed to effects of (i) electron collection due to hydrophobic interactions, (ii) electron transfer pathways due to π-conjugated bonds and (iii) enzyme stabilization due to π-hydrogen bonds that are newly induced by the PCA/GOx composite. The existence of such positive interactions is properly verified using X-ray photoelectron spectroscopy and enzyme activity measurements. NPG Asia Materials (2017) 9, e386; doi:10.1038/am.2017.75; published online 2 June 2017
INTRODUCTIONThe demand for clean electrical energy is increasing as a result of weather changes caused by the greenhouse effect and depletion of fossil fuels. 1 To meet this demand, related research and development efforts are being eagerly pursued. As one of the efforts, enzymatic biofuel cells (EBCs) that convert bioenergy into electrical energy are being considered. 2,3 In particular, EBC systems employing glucose oxidase (GOx) as a biocatalyst have emerged because of their advantageous properties, such as biocompatibility, excellent selectivity toward specific substrates and strong activity near neutral pH and room temperature. 2 In addition, because EBC systems use human body-friendly fuels, such as glucose, glycerol, water and oxygen, for electricity generation, they can be embedded as power generators for the operation of artificial internal organs, such as artificial hearts and brains, insulin pumps or bone stimulators. [4][5][6][7][8] However, in spite of such promising facets of EBC systems, the commercialization of EBCs using GOx has been limited because of their low EBC performance and poor durability. 9 The disadvantages are attributed to the low immobilization ratio of GOx molecules, slow GOx-related reaction rate, low GOx activity and easy GOx denaturation. Of them, low GOx immobilization has been considered the main problem.