Nitrite reduction and detection at a carbon paste electrode containing hemoglobin and colloidal gold
A novel renewable reagentless nitrite biosensor based on the direct electron transfer of hemoglobin (Hb) and a new sensing mechanism was proposed by combining the advantageous features of colloidal gold nanoparticle and carbon paste technology. The direct electrochemistry of immobilized Hb displayed a pair of redox peaks with a formal potential of −42 mV (vs. NHE) in 0.2 mol dm−3 NaAc–HAc buffer (pH 5.5). The immobilized Hb displayed an excellent response to the reduction of NO2− with one interfacial charge transfer followed by a chemical reaction (EC) mechanism. Under optimal conditions, the interfacial EC process could be used for the sensitive determination of NO2− with a linear range from 0.1 to 9.7 µmol dm−3 and a detection limit of 0.06 µmol dm−3 at 3σ. The amperometric determination of high concentrations of NO2− based on the irreversible reduction of NO could be performed at pH 4.0 with a linear range from 0.1 to 1.2 mmol dm−3. The surface of biosensor could be renewed quickly and reproducibly by a simple polish step. The biosensor has been used satisfactorily for nitrite determination in native water samples.