Nanoporous dual-electrodes with millimetre extensions: Parallelized fabrication and area effects on redox cycling

We present a nanoporous dual-electrode device for highly sensitive electrochemical detection via redox cycling. The individual sensors comprise one billion nanopores in an area of 9 mm². Pores feature an approximate lateral distance of 100 nm and pore radii down below 20 nm. The sensor's fabrication process is based on porous alumina membranes, which are formed via anodization of aluminum films. Novel processing steps are combined enabling high-throughput fabrication of the nanoporous sensors on the wafer scale. In this context, we present an electrochemical approach for the selective passivation of nanostructured electrode areas and introduce an etching process with tuneable selectivity for the removal of titania versus alumina. The devices exhibit sensitivities of up to 330 μA mM^-1 for the redox-active probe Fe(CN)₆^3-/4- making use of highly efficient redox cycling amplification inside the nanopores. Furthermore, the large-scale interplay of the sensor's nanopores in millimetre dimensions facilitates analyte enrichment and depletion at the sensor surface. The large-area sensor therefore provides an interesting opportunity for determining the oxidation-state- dependent diffusion coefficients of redox-active molecules.