Enzyme biosensor based on an N-doped activated carbon fiber electrode prepared by a thermal solid-state reaction

The sensitivity of a biosensor electrode was increased by introducing hydrophilic N-groups onto the surface of a polyacrylonitrile (PAN) based activated carbon fiber. The electrospun carbon fiber was activated using KOH to improve the adsorption of glucose oxidase (GOx) enzymes through pore production and the introduction of oxygen functional groups. The activated carbon fibers (ACFs) were then reacted with urea to increase their hydrophilicity by doping their nitrogen groups. The sensor sensitivity and the Michaelis-Menten constant, Km, were altered by varying the percentages of functional groups on the electrode surfaces. Whereas the value of Km was affected by the kind of functional groups, the sensitivity of the biosensor electrode was chiefly affected by the amount of functional groups introduced urea modification because the enzyme was better immobilized onto urea-modified activated carbon fibers. Quantitatively, the sensitivity was two- to three-fold higher for the biosensors based on urea-treated ACFs than those based on untreated ones. This increased sensitivity is attributed to the nitrogen and oxygen functional groups on the urea-modified ACFs.