Direct electron transfer kinetics of histamine dehydrogenase at air plasma-treated graphite nanofibers

•Electron transfer kinetics at exposed edge planes of graphite nanofibers.•Improvement of direct electrochemical communication between enzymes and electrodes.•Application to 3rd generation biosensors. As histamine is one of the important mediators for allergic reactions, its efficient detection methods and real-time monitoring systems are required for food analyses and drug discoveries to suppress allergic reactions. Although histamine dehydrogenase (HmDH) is a promising candidate for developing enzyme-based electrochemical biosensors, some electron mediators are frequently employed to observe electrocatalytic currents for histamine oxidation. Here, direct electrochemistry of HmDH was studied at the surface of graphite nanofibers (GNFs), which provide active reaction sites for redox species. Air plasma-treated GNFs were used for constructing a three-dimensional network that works both as an electrical nanowire and an enzyme support. Even though the amount of oxygen-containing functional groups didn’t significantly increase at the GNF surface with increase in the air plasma treatment time, direct electron transfer from reduced HmDH by histamine to the GNFs was improved probably due to capped and curvature of the graphite edge sites with oxygen-containing functional groups, which were generated by the air plasma treatment. The air plasma-treated GNFs also allowed enhancement of the complex-formation reaction rate of HmDH with histamine, as the air plasma treatment time increased.