Preparation and Electrochemical Characterization of an Enzyme Electrode Based on Catalase Immobilized onto a Multiwall Carbon Nanotube‐Thionine Film

The present study was aimed at investigating the use of a mixture multiwall carbon nanotube (MWCNT) and thionine (Th) dye in designing of a thionine‐based electrochemical biosensor containing catalase (Ct) enzyme (MWCNT‐Nafion‐Th/Ct) onto a glassy carbon electrode (GCE). The effects of pH, MWCNT concentration and thionine concentration on electrochemical response were explored for optimum analytical performance. The modified electrode exhibited a pair of well‐defined, quasi‐reversible peaks at formal potential (E o ′) = ‐0.218 ± 0.017 V vs. Ag/AgCl corresponding to the Th ox /Th red redox couples in the presence of MWCNT, Nafion, and Ct. The electrochemical parameters, including charge‐transfer coefficient (0.36), and apparent heterogeneous electron transfer rate constant (4.28 ± 0.26 s −1 ) were determined. Using differential pulse voltammetry, the prepared enzyme electrode exhibited a linear response to hydrogen peroxide (H 2 O 2 ) in the range of 10.0‐100.0 μM with a detection limit 8.7 μM and a sensitivity of 6051.0 μA mM −1 cm −2 .