Nitrite reduction and detection at a carbon paste electrode containing hemoglobin and colloidal gold

Abstract

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.