Integrated Probe For Electrochemical Analysis Of Small Volume Droplets

Analysis of small volume droplets is increasingly important in biology, environment, and material science. In this work, an integrated probe consisting of a Pt microelectrode wrapped with an Ag/AgCl wire and inserted into an outer capillary filled with KCl is developed as sensor for electrochemical analysis of small volume droplets (20 mu L). With a 3D-printed holder, the design allows easy fabrication, dismantling and re-assembly, which is important for renewing the probe. The integrated probe shows acceptable ohmic drop with electrochemical impedance spectroscopy, thus offers reliable and reproducible potentiometric and voltammetric measurements in bulk solutions. The ring-shaped opening between the inner microelectrode and the outer capillary also enables homogenous current distribution when applying potential between Pt and Ag/AgCl. Based on this, two droplet systems mimicking atmospheric corrosion are in-situ studied: (1) Fe3+ droplet on bare and silane-coated steel; (2) Cu2+ in a H2SO4 droplet on copper. The concentration of Fe3+/Fe2+ and Cu2+ in the droplet is monitored with time, allowing interfacial corrosion reactions between the droplet and the substrate to be studied.