Hemoglobin (Hb) was entrapped in a phosphatidylcholine (PC) film and immobilized at a pyrolytic graphite (PG) electrode surface. Its electron-transfer reactivity and enzyme activity were characterized by employing electrochemical methods. It was observed that Hb exhibited direct electrochemistry as well as enzyme-like activity towards the electrocatalytic reduction of NO in PC film. An unmediated, reagentless nitrogen oxide (NO) biosensor was accordingly prepared. Experimental results revealed that the peak current related to NO was linearly proportional to its concentration in the range of 1.0 x 10(-7)-3.0 x 10(-4) mol/L. The detection limit was estimated to be 1.0 x 10(-7) mol/L. Considering its good stability, nice selectivity and easy construction, this biosensor shows great promise for the rapid determination of traces of NO.

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An unmediated NO biosensor was prepared by co-immobilizing haemoglobin with polyethyleneimine at a pyrolytic graphite electrode surface. Haemoglobin exhibits direct electrochemistry in the membrane, and this modified electrode shows high stability and catalytic activity towards the reduction of NO. A linear relationship between the catalytic current and the concentration of NO was observed in the concentration ranges 1.0 x 10(-7)-8.0 x 10(-6) M and 1.0 x 10(-5)-2.5 x 10(-5) M, with a detection limit of 4.0 x 10(-8) M.

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