A norepinephrine biosensor based on a glassy carbon electrode modified with carbon nanotubes

Immobilized enzyme tyrosinase on single-walled carbon nanotubes (SWCNTs) was used to measure the norepinephrine concentration in injections. A simple method was investigated to prepare a modified glassy carbon (GC) electrode with CNTs. First, CNT solution was cast on the electrode surface and dried to form a CNT/GC electrode. Then, tyrosinase (TR) immobilized on the surface of the CNT/GC electrode. The cyclic voltammograms (CVs) in aqueous solution indicated that the CNTs could promote the direct electron transfer of tyrosinase and a pair of stable redox couple appeared. Tyrosinase can catalyze the oxidation of norepinephrine to norepinephrine quinone. When norepinephrine was added to the electrochemical cell, the oxidation peak current of the TR/SWCNT/GC electrode increased and gives a catalytic current. Based on this, a biosensor for determination of norepinephrine has been developed. This method had adequate accuracy, sensitivity and precision; in addition, the biosensor showed good repeatability and stability to assay norepinephrine in bulk form and pharmaceutical dosage forms.