Electrochemical detection of NO by inhibition on oxidase activity

An inexpensive and simple nitric oxide amperometric sensor for the determination of the inhibitory effects of nitric oxide (NO) on xanthine oxidase (XOD), horseradish peroxidase (HRP), polyphenol oxidase (PPO) and glucose oxidase (GOX) is described. Each enzyme has been immobilized on either carbon paste electrode (CPE) or platinum microelectrode by electropolymerization. The inhibition was first performed against each enzyme, using 2 mM NO for its concentration at saturation on 0.1 M phosphate buffer (pH 7.4) and then the quantification of the inhibition was determined in the range of 0-2 mM. The results showed that the enzymes were inhibited by NO in the studied range leading to the complete loss of enzyme activity at 2 mM. Thus, the decrease in activity of the enzymes monitored can be correlated to the concentration of NO present in solution. The effect of NO treatment time on inhibition was also demonstrated (i.e., GOX loses 80 % of its activity in 2 mM NO in 60 s). When the loss of activity for each enzyme was compared in the presence of 250 μM NO, the order of the amperometric signals obtained are as follows: PPO > GOX > HRP > XOD.