Fabrication of microelectrode arrays for in situ sensing of oxidation reduction potentials

There is a clear need for in situ monitoring of oxidation–reduction potential (ORP) in many environmental applications, particularly those involving water quality monitoring and wastewater treatment. This paper describes fabrication of microelectrode sensor arrays for measurements of ORP in situ in the environment, such as at Superfund sites. The four-probe microelectrode arrays were fabricated from glass using a two-step, HF-based meniscus etching process. The tip size of individual microelectrodes was approximately 200 nm. The electrochemical performance of these ORP electrodes was fully characterized by measuring redox potentials of standard and reference solutions. When compared with commercial milli-electrodes, the microelectrode arrays exhibited very fast response time (from a few milliseconds to 30 s) and proved to be extraordinarily stable (variability on the order of 2 mV over a 4-day test period). This successful development of microelectrode arrays for ORP measurements will enable in situ measurement of redox potentials in the environment, such as contaminated soils, biofilm or sediments at Superfund sites.