Nitric oxide (NO) plays a key role in many biological processes, such as vasodilation, blood pressure and neural communication. It has been proven that, amongst others, respiratory diseases, cardiovascular diseases and hypertension are related to the concentration of NO.
The amperometric Clark electrode is the best known electrochemical oxygen sensor. The reduction of oxygen at the working electrode yields an electric current proportional to the oxygen concentration. The addition of a semi-permeable membrane (e.g., PTFE) serves two purposes: increased selectivity and a static current response. The latter can also be achieved by the use of ultra-micro-electrodes. Alternatively, selectivity can be enhanced by the use of ultra-fast scanning techniques, suppressing any redox reactions with slower kinetics than the fast oxygen reduction.
Potentiometric pH sensing can be achieved by several means. One of them is the use of conducting polymers such as polypyrrole or (poly) indole, electrodeposited on a platinum working electrode. Alternatively, the use of metal oxides such as iridium oxide form good candidates for miniaturized pH electrodes.