Array of individually addressable two-electrode electrochemical cells sharing a single counter/reference electrode for multiplexed enzyme activity measurements

This work reports on the fabrication and performance of a new on-chip array of gold thin-film electrodes arranged into five individually addressable miniaturized electrochemical cells. Each cell shows a two-electrode configuration comprising a single working electrode and a counter/pseudo-reference electrode that is compartmentalized to be shared among all the cells of the array. Using this configuration, just six contact pads are required, which significantly reduces the chip overall surface area. Electrochemical characterization studies are carried out in solutions containing the two species of reversible redox pairs. The concentration of one redox species can reliably be measured at the working electrode by applying potentiostatic techniques to record the current due to the corresponding electrochemical reaction. The redox counterpart in turn undergoes an electrochemical process at the counter/pseudo-reference electrode, which, under optimized experimental conditions, injects current and keeps the applied potential in the electrochemical cell without limiting the current being recorded at the working electrode. Under these conditions, the electrode array shows an excellent performance in electrochemical detection studies without any chemical or electrical cross-talk between cells. The enzymatic activity of horseradish peroxidase, alkaline phosphatase and myeloperoxidase enzymes is analyzed using different redox mediators. Quasi-simultaneous measurements with the five electrochemical cells of the array are carried out within 1 s time frame. This array layout can be suitable for multiplexed electrochemical immunoassays and immunosensor approaches and implementation in simplified electrochemical ELISA platforms that make use of enzyme labels. Moreover, the array reduced dimensions facilitate the integration into compact fluidic devices.