Nanocavity crossbar arrays for parallel electrochemical sensing on a chip

Abstract

SummaryWe introduce a novel device for the mapping of redox-active compounds at high spatial resolution based on a crossbar electrode architecture. The sensor array is formed by two sets of 16 parallel band electrodes that are arranged perpendicular to each other on the wafer surface. At each intersection, the crossing bars are separated by a ca. 65 nm high nanocavity, which is stabilized by the surrounding passivation layer. During operation, perpendicular bar electrodes are biased to potentials above and below the redox potential of species under investigation, thus, enabling repeated subsequent reactions at the two electrodes. By this means, a redox cycling current is formed across the gap that can be measured externally. As the nanocavity devices feature a very high current amplification in redox cycling mode, individual sensing spots can be addressed in parallel, enabling high-throughput electrochemical imaging. This paper introduces the design of the device, discusses the fabrication process and demonstrates its capabilities in sequential and parallel data acquisition mode by using a hexacyanoferrate probe.

Electric and Electrochemical Microfluidic Devices for Cell Analysis

“…Although numerous reports have described such devices in which the electrodes are simply arranged, with useful applications in cell analysis, including neurons (Kasai et al, 2005), the areas of the leading electrodes and connector pads are large, which limits the density and number of electrodes that can be incorporated. Recently, several kinds of integrated electrode arrays have been developed to overcome this limitation (Ino et al, 2012, 2014; Kätelhön et al, 2014; Kanno et al, 2015c; Zhang et al, 2017). These systems can provide electrochemical images consisting of 2D current values.…”

“…For example, nanopores were used for measuring oligonucleotides and microvesicles via detection of ion currents when passing through the pores (Anderson et al, 2015; Kawano, 2018). For highly sensitive and selective assays, a redox cycling system was used in nanofluidic and nanocavity devices including two sets of electrodes in close proximity to one another (Lemay et al, 2013; Kätelhön et al, 2014; Kanno et al, 2015c). A redox species generated at one electrode diffuses to the other electrode, which generates an electrochemical reaction to regenerates the original species, resulting in signal amplification.…”

Fabrication of a Horizontal and a Vertical Large Surface Area Nanogap Electrochemical Sensor

“…The majority of longer horizontal nanogap devices are fabricated using either EBL or FIB. Vertical nanogap devices for electrochemical sensing applications have, in particular, been pioneered by the groups of both Lemay [19,20,26] and Wolfrum [19,20,27,28,29]. By far the most popular method for the fabrication of vertical nanogap devices involves etching away a sacrificial layer between two electrode layers.…”

High-Density Droplet Microarray of Individually Addressable Electrochemical Cells

“…A remarkably high density of testing points can be achieved because multiple measurement points share the same wires to the external circuit. Several addressable microarray electrode systems have been reported since then, including orthogonal microband electrode arrays with microwell, vertically separated electrode array, interdigitated electrode array, , ring–ring electrode array, , ring-disk electrode array, nanocavity crossbar arrays, and droplet arrays on comb-type interdigitated ring array electrodes …”

“…A remarkably high density of testing points can be achieved because multiple measurement points share the same wires to the external circuit. Several addressable microarray electrode systems have been reported since then, including orthogonal microband electrode arrays with microwell, 20 vertically separated electrode array, 21 interdigitated electrode array, 22,23 ring−ring electrode array, 24,25 ring-disk electrode array, 26 nanocavity crossbar arrays, 27 and droplet arrays on comb-type interdigitated ring array electrodes. 28 In these systems, the electrochemical signal is based on the redox cycling of chemically reversible redox couples between the two electrodes, which results in signal amplification related to multiple oxidation and reduction processes for each analyte molecule.…”