Electrochemical behaviour of Cu/CuSe microelectrode and its application in detecting temporal and spatial localisation of copper(II) fluxes along Olea europaea roots.

The electrochemical behaviour of a Cu/CuSe electrode was studied in order to define its selectivity towards cupric ions, Nerstian response, limit of detection and response time. The chalcogenide electrode was prepared by cathodic deposition of Se and subsequent formation of a thin layer of CuSe on a copper substrate. A Cu/CuSe microelectrode was prepared using copper wire 75 μm in diameter. The dimensions and response time (<0.5 s) allowed use of this electrode in the “vibrating probe method” with the aim of measuring net influxes as well as effluxes of copper(II) ions in Olea europaea roots. The electrode potential was measured along the root at a distance of 5 μm from the surface for 5 s, and then again for 5 s at a distance of 55 μm, moving the microelectrode with respect to the root surface by steps with a frequency of 0.1 Hz. The potentials measured at the two extremes of vibration were then converted to copper(II) concentrations. Substitution of these values in Fick's law yields the flux, assuming the diffusion constant D for copper ions in aqueous solutions. The results enabled us to detect copper(II) fluxes as small as 0.05 pmol cm−2 s−1. Copper(II) influx showed marked spatial and temporal features: it was highest at about 1.5 mm from the root apex and exhibited an oscillatory pattern in time.