Ionic-liquid/NH2-MWCNTs as a highly sensitive nano-composite for catalase direct electrochemistry

A nano-composite material consisting of amine functionalized multi-walled carbon nanotubes and a room temperature ionic-liquid (1-butyl-3-methylimidazolium tetrafluoroborate) was prepared and used to construct a novel catalase (Ct) based biosensor for the determination of hydrogen peroxide. The modified electrode exhibited a quasi-reversible cyclic voltammogram corresponding to the Fe(II)/Fe(III) redox couple in the heme prosthetic group of Ct with a formal potential of −460 mV in 0.1 M phosphate buffer solution at pH 7.0. The nano-composite film showed an obvious promotion of the direct electron transfer between Ct and the underlying electrode. The apparent charge transfer rate constant and transfer coefficient for electron transfer between the electrode surface and enzyme were calculated as 2.23 s−1 and 0.45, respectively. The immobilized Ct exhibited a relatively high sensitivity (4.9 nA/nM) toward hydrogen peroxide. Under the optimized experimental conditions, hydrogen peroxide was detected in the concentration range from 8.6 to 140 nM with a detection limit of 3.7 nM at S/N = 3. The modified electrode was stable for two weeks with no observable change in the cyclic voltammograms.