CHEMICALLY-MODIFIED MICROELECTRODES DESIGNED FOR THE ELECTROCHEMICAL DETERMINATION OF NITRIC-OXIDE IN BIOLOGICAL-SYSTEMS

Since the identification of nitric oxide (NO) as an endothelial-derive d relaxing factor, several research groups are now working to develop an understanding of the mechanism by which this free-radical gas is sy nthesized, diffused and reacted from and within various cells and diff erent biological tissues. Thus, it appears that measuring NO in biolog ical models is very difficult because of its low concentration and fle eting existence. Indeed, NO directly reacts extremely fast with supero xide and other very active free radicals of biological importance. Mos t of the techniques for assaying NO release use indirect methods for e stimating endogeneous NO, relying on measurements of secondary species . In fact, NO in biological systems may be directly assayed by three n onelectrochemical strategies (EPR, spectrophotometry and chemiluminesc ence) but these strategies suffer from being ex situ detection techniq ues with poor selectivity or sensitivity. The desire to measure a smal l amount of NO release in situ has led to an active area of research i nvolving the design of microsensors and new amperometric microelectrod e probes are now developed to detect NO. The use of electrochemistry a s a potential way to do so is very promising and the reality is that s urface electrode modification is needed to make the electrode material selective for NO. Therefore, the design of modified electrode surface s using organized layers combined with microelectrodes is attractive a s possible selective microsensors for the electrochemical detection of NO. A number of new amperometric approaches have reached this goal. T his article consists of a critical review of electrochemical methods f or the detection and determination of nitric oxide in biological mater ials to clarify some aspects of the reported microsensors.