Optimization of carbon nanotube layer formation on plasma-polymerized thin film for enzyme biosensor

An electrochemical biosensor based on a carbon nanotube (CNT) layer with glucose oxidase (GQx) enzyme sandwiched between 6-nm-thick acetonitrile plasma-polymerized films (PPFs) was fabricated. The lower PPF was deposited onto a sputtered gold electrode. The optimization of the casting formation of the CNT layer onto the lower PPF is addressed. As a result, the best candidate for the casting solution was a 1:1 mixture of phosphate buffer and ethanol, and the optimized CNT concentration was 7.5 mg ml^-1. The optimized glucose biosensor characteristics exhibited ultrasensitivity (a sensitivity of 11 μA mM^-1 cm^-2 (4.9-19 mM), a detection limit of 6.2 μM at S/N = 3, +0.8 V vs Ag/AgCl), and a rapid response (< 4 s to reach 95% of maximum response). This high performance is attributed to the excellent electrocatalytic activity and enhancement of electron transfer that CNTs provide, and because the PPF and/or plasma process for CNTs are an enzyme-friendly platform.