Carbon nanotube-plasma polymer-based amperometric biosensors: Enzyme-friendly platform for ultrasensitive glucose detection

An amperometric enzyme biosensor fabricated with carbon nanotubes (CNTs) and plasma-polymerized thin films (PPFs) is reported. A mixture of the enzyme glucose oxidase (GOD) and a CNT film is sandwiched with 10-nm-thick acetonitrile PPFs. Under PPF layer was deposited onto a sputtered gold electrode. To facilitate the electrochemical communication between the CNT layer and GOD, CNT was treated with oxygen plasma. The device with single-walled CNTs showed a sensitivity higher than that of multimalled CNTs. The glucose biosensor showed ultrasensitivity (a sensitivity of 40 mu A mM(-1) cm(-2), a correlation coefficient of 0.992, a linear response range of 0.025-1.9 mM, a detection limit of 6.2 mu M at S/N = 3, +0.8 V vs Ag/AgCl), and a rapid response (< 4 s in reaching 95% of maximum response). This high performance is attributed to the fact that CNTs have excellent electrocatalytic activity and enhance electron transfer, and that PPFs and/or the plasma process for CNTs are the enzyme-friendly platform, i.e., a suitable design of the interface between GOD and CNTs.