Electronically\nType-Sorted Carbon Nanotube-Based Electrochemical\nBiosensors with Glucose Oxidase and Dehydrogenase

Abstract

An electrochemical enzyme biosensor\nwith electronically type-sorted\n(metallic and semiconducting) single-walled carbon nanotubes (SWNTs)\nfor use in aqueous media is presented. This research investigates\nhow the electronic types of SWNTs influence the amperometric response\nof enzyme biosensors. To conduct a clear evaluation, a simple layer-by-layer\nprocess based on a plasma-polymerized nano thin film (PPF) was adopted\nbecause a PPF is an inactive matrix that can form a well-defined nanostructure\ncomposed of SWNTs and enzyme. For a biosensor with the glucose oxidase\n(GOx) enzyme in the presence of oxygen, the response of a metallic\nSWNT-GOx electrode was 2 times larger than that of a semiconducting\nSWNT-GOx electrode. In contrast, in the absence of oxygen, the response\nof the semiconducting SWNT-GOx electrode was retained, whereas that\nof the metallic SWNT-GOx electrode was significantly reduced. This\nindicates that direct electron transfer occurred with the semiconducting\nSWNT-GOx electrode, whereas the metallic SWNT-GOx electrode was dominated\nby a hydrogen peroxide pathway caused by an enzymatic reaction. For\na biosensor with the glucose dehydrogenase (GDH; oxygen-independent\ncatalysis) enzyme, the response of the semiconducting SWNT-GDH electrode\nwas 4 times larger than that of the metallic SWNT-GDH electrode. Electrochemical\nimpedance spectroscopy was used to show that the semiconducting SWNT\nnetwork has less resistance for electron transfer than the metallic\nSWNT network. Therefore, it was concluded that semiconducting SWNTs\nare more suitable than metallic SWNTs for electrochemical enzyme biosensors\nin terms of direct electron transfer as a detection mechanism. This\nstudy makes a valuable contribution toward the development of electrochemical\nbiosensors that employ sorted SWNTs and various enzymes.