The use of gold electrodes in the electrochemical detection of nitric oxide in aqueous solution

It was recently discovered that vascular endothelial cells could synthesize the free-radical gas nitric oxide (NO) [1,2] and since that discovery, it has been possible to demonstrate the considerable physiological importance of NO as for example in the control of human blood flow and pressure. Several works are now dealing with the understanding of the mechanism by which NO is synthesized [3]. As a matter of fact, it has appeared that measuring NO in biological models is very difficult because of its low stability and high fugacity. In a recent review Archer [4] has summarized the different NO measurement strategies reported in the literature. The most widely used techniques involve the ex-situ detection of NO by (i) electron paramagnetic resonance, (ii) spectrophotometry and (iii) chemiluminescence. New amperometric microelectrode probes are now developed to detect NO and the use of electrochemistry, as a potential way to do so is very promising. Indeed, ultramicroelectrode design and elaboration are now reaching very high levels of sophistication [5] contributing very actively to the promotion of the use of the electrochemical techniques for in vivo NO detection in intact tissues and from single cells. There are two amperometric methods reported in the literature for measuring NO in vitro and from tissues and single cells. The first method is based on the direct oxidation of NO on platinum electrode. Shibuki [6] reported the detection of NO by using a miniature Clark-type electrode. The electrode was designed by introducing a platinum wire within a pipette with a fire-polished 150-250 pm tip (with a thin chloroprene rubber seal) filled with an aqueous solution of 30 mM NaCl and 0.3 mM HCI. The platinum indicator electrode was placed as close as possible to