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Although heme protein-based, amperometric nitric oxide (NO) biosensors have been well documented in previous studies, most have been conducted in anaerobic conditions. Herein we report a novel hemoglobin-based NO biosensor that is not only very sensitive but also usable in air. The heme protein was entrapped in a sodium montmorillonite film, which was immobilized at a pyrolytic graphite electrode surface. Film-entrapped hemoglobin can directly exchange electrons with the electrode, and this process has proven to favor the catalytic reduction of oxygen. In addition, NO induced a cathodic potential shift of the catalytic reduction peak of oxygen. This potential shift was proportional to the logarithm of NO concentration ranging from 4.0 × 10−11 to 5.0 × 10−6 mol/L. The detection limit has been estimated to be 20 pM, approximately four orders lower than previously reported amperometric detectors.

Direct electron transfer of hemoglobin (Hb) can be achieved in a Hb/montmorillonite (MMT)/polyvinyl alcohol multi-assembly at a pyrolytic graphite (PG) electrode. Accordingly, a novel nitric oxide (NO) biosensor is proposed. The reduction of NO is observed at a potential of approximately -783 mV (vs. SCE) at pH 5.5. At optimum pH, this biosensor shows a wide linear range of 1.0x10(-6)-2.5x10(-4) mol/l with a detection limit of 5.0x10(-7) mol/l. The sensor-to-sensor reproducibility is good consideringmacr; a relative standard deviation of 3.5% in five independent determinations at 5.0x10(-5) mol/l NO. The modified electrode is conveniently constructed and durable in long-term operations.

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.

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.