Wireless Electrochemical DNA Microarray Sensor

Abstract

Here we report an electrochemical DNA microarray sensor whose function is controlled using just two wires regardless of the number of individual sensing electrodes. This advance is enabled by confining bipolar sensing electrodes within a microfluidic channel (part a of Scheme 1) and exerting potential control over the electrolyte solution rather than individual electrodes. In this configuration, the two driving electrodes control the potential difference between the sensing electrodes and the solution, and the current at the sensing electrodes is indirectly measured by taking advantage of electrogenerated chemiluminescence (ECL) present at the anode end of each bipolar electrode. In this communication, we show that this approach can be used to sense hybridization of DNA oligonucleotides.Electrochemistry is normally carried out by controlling the electrode potential. However, because the potential difference between the electrode and the solution drives the electron-transfer reaction, it is equally effective to control the potential of the solution. Our approach for using this principle is illustrated in part b of Scheme 1. 1,2 An external potential (E tot ) is applied to the two ends of a microchannel, and the resistance of the electrolyte solution results in a linear potential gradient (dE/dx) along the channel. The difference in potential between the two ends of the bipolar electrode (∆E elec ) is the fraction of E tot dropped across the length of this electrode (L elec ). If ∆E elec is sufficiently large, then faradaic electrochemical processes will occur simultaneously at both ends of the bipolar electrode. Because of the requirement for charge balance, the rate of electron transfer (i.e., the current) at both ends of the electrode must be the same.A significant deficiency of bipolar electrochemistry is that there is no means for directly measuring current flowing within an electrode. 1,2 The experimental configuration illustrated in part c of Scheme 1 addresses this problem. Here, E tot is held at a sufficiently high value that the ECL reaction resulting from the oxidation of Ru(bpy) 3 2+ and tri-n-propylamine (TPrA), 3-5 indicated at the anode end of the bipolar electrode, is activated upon electrocatalytic reduction of O 2 at the cathode end of the electrode. In the sensing experiments discussed next, the oxygen reduction reaction (ORR) is catalyzed by hybridization of target DNA labeled with Pt nanoparticles (Pt-NPs) to previously immobilized capture DNA. 6 Accordingly, in the presence of DNA hybridization at the cathode, light is emitted from the anode.Part a of Figure 1 shows that the sensor consists of a microfluidic device and three Au electrodes. The poly(dimethylsiloxane) (PDMS) microfluidic device was prepared by a standard micromolding method. 7 The microchannel was 12 mm long, 1.75 mm wide, and 26 µm high. The three Au electrodes (1.00 × 0.25 mm) were microfabricated on a glass slide and configured parallel to one another at the center of the channel. Two Pt wires were placed in reservoirs at ei...

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