A Nitrite Biosensor Based on Coimmobilization of Nitrite Reductase and Viologen-Modified Polysiloxane on Glassy Carbon Electrode

Copper containing nitrite reductase (Cu-NiR) and viologen-modified sulfonated polyaminopropylsiloxane (PAPS-SO3H-V) were co-immobilized on glassy carbon electrode (GCE) by hydrophilic polyurethane (HPU) drop-coating, and the electrode was tested as a reagentless electrochemical biosensor for nitrite detection. The newly synthesized PAPS-SO3H-V as an electron transfer (ET) mediator between electrode and NiR was effective, and could be effectively immobilized in HPU membrane. The NiR and PAPS-SO3H-V co-immobilized GCE used as a nitrite biosensor showed the following performance factors: sensitivity = 12.0 nA mu M-1, limit of detection (LOD) = 60 nM (S/N = 3), linear response range = 0-18 mu M (r(2) = 0.996) and response time (t(90%)) = 60 s, respectively. Lineweaver-Burk plot shows that apparent Michaelis-Menten constant (K-M(app)) is 101 mu M. Storage stability of the sensor is 51 days (80% of initial activity) in condition of storing in ambient air at room temperature. The sensor showed a relative standard deviation (RSD) of 3.2% (n = 5) even in condition of injection of 1 mu M nitrite. Interference study showed that common anions in water sample such as chlorate, chloride, sulfate and sulfite do not interfere with the nitrite detection. However, nitrate interfered with a relative sensitivity of 80% due to inherent character of the enzyme used.