A novel nitrite biosensor based on the direct electron transfer of hemoglobin immobilized on CdS hollow nanospheres

A novel nitrite biosensor based on the direct electron transfer of hemoglobin (Hb) immobilized on CdS hollow nanospheres (HS-CdS) modified glassy carbon electrode was constructed. The direct electron transfer of Hb showed a pair of redox peaks with a formal potential of -286 mV (vs. SCE) in 0.1 M pH 7.0 phosphate buffer solution. It was a surface-controlled electrode process involving a single proton transfer coupled with a reversible one-electron transfer for each heme group of Hb. HS-CdS had a large specific surface area and good biocompatibility and had a better electrochemical response than that of solid spherical CdS. The immobilized Hb on HS-CdS displayed an excellent response to NO₂^- with one irreversible electrode process for NO reduction. Under optimal conditions, the biosensor could be used for the determination of NO₂^- with a linear range from 0.3 to 182 μM and a detection limit of 0.08 μM at 3σ based on the irreversible reduction of NO. HS-CdS provided a good matrix for protein immobilization and had a promising application in constructing sensors.