Scalable fabrication and application of nanoscale IDE-arrays as multi-electrode platform for label-free biosensing

The continuous progress in the construction of advanced, miniaturized electrodes provides a promising route towards compact and sensitive biological and chemical sensor platforms. We present a combined micro- and nanofabrication process at wafer-scale with nanoimprint lithography and subsequent photolithography for the realization of ultra-small, interdigitated electrode arrays. Several chips of gold nanoelectrode arrays (NEA) in a 4 × 4 configuration designed as interdigitated electrodes (NEA-IDEs) with finger structures measuring 14 μm in length and 600 nm in width with 600 nm spacing were fabricated simultaneously on 4-inch wafers. Our process involved a nanoimprint lithography step, wet-etching, metal evaporation and nano lift-off followed by optical lithography for metal contact lines and passivation layers. The optimized procedure yielded high-quality NEA-IDEs with reliable electrochemical behavior as inferred from voltammetric and impedimetric analysis. The final array allows the control of all 16 NEA-IDEs in parallel, which can be beneficial for multi-analyte detection. In a proof-of-concept assay, to demonstrate the applicability of the NEA-IDEs for biosensing, the nanostructures were modified with short DNA molecules as recognition elements for the detection of hybridization via impedance spectroscopy. Stable impedance signals were found using the redox system ferri-/ferrocyanide. After hybridization with complementary target DNA the sensors showed an enhancement of the charge transfer resistance. Experiments with different target DNA concentrations demonstrated a dynamic detection range of 1-100 nM. The main advantage of these NEA-IDE structures is that they are small enough to be integrated into typical microchannel dimensions of 50-100 μm for miniaturized lab-on-a-chip biosensor devices in future.