A novel nano-interfaced superoxide biosensor

A nano-interfaced biosensor for superoxide (O2−) was developed based on superoxide dismutase (SOD) immobilized on iron oxide nanoparticles (nano Fe3O4) coated on a gold electrode surface. Nano Fe3O4 were synthesized via hydrothermal method and superoxide dismutase enzyme (SOD) was attached to it by covalent linking. FT-IR, FE-SEM and XRD have been used for morphological and structural characterization of nano Fe3O4. The modified electrode was used to detect superoxide radicals generated using sodium hydroxide and dimethyl sulfoxide. The cyclic voltammetry studies of the SOD/nano Fe3O4/Au bioelectrode exhibited an electrochemical reduction behavior for increasing concentrations of SOD at a scan rate of 0.1 V/s in a cell containing 5 mL phosphate buffer solution (pH 7.4). Amperometric studies revealed that the nano-interfaced bioelectrode displayed a sharp response time of 4 s with a limit of detection (LOD) as 3.46 nM and limit of quantification as (LOQ) as 11.5 nM. The response is found to be linear in the range of 0.2–1.4 μM superoxide. The sharp response time is attributed to the fact that a rapid and direct electron transfer between the SOD tagged nano Fe3O4 and the gold electrode without any redox mediator. The biosensor also exhibited good reproducibility, stability and shelf life.