Fully integrated on-chip nano-electrochemical devices for electroanalytical applications

Abstract

In this work, we report a fully integrated nanowire-based electrochemical device that enables a suite of highly sensitive electroanalytical techniques in small sample volumes at silicon chip substrates. A hybrid wafer-level lithography approach is employed whereby an array of twelve individually addressable discrete gold nanowire electrodes, written by electron beam lithography, along with on-chip gold counter and silver pseudo-reference electrodes are deposited on silicon chips. An inorganic silicon nitride passivation ensures the devices are compatible with both aqueous and organic media. Peripherally located probe pads enables facile and direct electrical connection to electrodes using a reusable push-pin interface within a bespoke sample holder. This approach eliminates the requirement for costly microelectronic packaging techniques and also the requirement for large volume sample analysis. Nanowire electrodes with highly reproducible dimensions and low surface roughness are routinely fabricated and display characteristic Ohmic responses during two-point I–V measurements. The magnitude and shape of the voltammetric responses of a model molecule ferrocene monocarboxylic acid at nanowire electrodes were found to be highly reproducible on different electrodes and chips from multiple wafers and fabrication runs. Quasi-steady-state electrochemical behaviour was demonstrated for scan rates up to 5000mVs−1, without any observed changes to the voltammetric shape, enabling the potential for reliable electroanalysis with a millisecond response time. Square wave voltammetry was applied to the detection of 2,4-dinitrotoluene in the absence of a supporting electrolyte. Devices exhibited excellent limit of detection of 7ngmL−1 using pristine unmodified nanowire electrodes. Consequently, these integrated nano-electrochemical devices represent a platform excellently positioned for providing reliable, rapid electroanalytical sensing suitable for a wide range of analytical applications.