Separation of Electrochemical Signals By Ohmic Drop between Electrodes Arranged in a Matrix Configuration

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1.introduction Combining electrochemical principles and microfabrication techniques can achieve high sensitivity and miniaturization of sensing devices. However, commonly used three-electrode systems increase the number of contacts paid and manufacturing costs with the integration of electrodes. Array electrodes are advantageous as a solution to this problem. Array electrodes share contact pads, making them easy to integrate and suitable for multiple detections. The single-channel array electrode electrochemical system used in this study (Figure 1a) consists of an array electrode as the detection part and a polydimethylsiloxane (PDMS) flow channel as the separation signal part. In previous studies of array electrodes, multi-channel was used to separate the signals, and no attempt was made to achieve the separation of electrochemical signals in the same channel. This study achieved signal separation within a single channel by controlling the ohmic drop. 2.Experimental Figure 1a shows the equipment used in this study. Four working electrode platinum strips and two platinum counter electrodes were formed orthogonally. The silver strip of the reference electrode is inserted between the working and counter electrodes. The polyimide layer opens at the orthogonal intersections. These 8 openings form 8 detectable electrochemical sensing regions.In order to investigate the impact of ohmic voltage drop, a polydimethylsiloxane (PDMS) flow channel was devised. As shown in Figure 1b, the left working electrode was deliberately insulated, leaving only the right working electrode operational. The large ohmic drop case and the small ohmic drop case can be obtained by changing the left and right reference electrodes and counter electrodes.As the working electrodes used for detection are moved away from the reference electrodes, the ohmic drop becomes larger. When the working electrodes used for detection are located away from the reference electrodes, the ohmic drop becomes larger. At this working electrode, oxidation or reduction reactions are difficult to realize because of the large ohmic drop. As a result, the signals at the sensing site used for detection (intersection point) will be separated and detected. To discern the effects of varying ohmic drops, cyclic voltammetry（CV）and differential pulse voltammetry (DPV) data were collected. This involved the systematic replacement of both the left and right reference electrodes as well as the counter electrodes. K4[Fe(CN)6] was used to obtain the peak current and KCl was used as the electrolyte. 3.Result and Discussion Figure 1c shows the differential pulse voltammetry results obtained for the sensing region within the PDMS flow channel. A clear current peak can be seen in the small ohmic drop case, and almost no current change can be observed in the large ohmic drop case. The sensing regions at the intersections have a small ohmic drop and the sensing regions work normally. The non-crossing sensing region is affected by a large ohmic voltage drop and cannot reach the oxidation or reduction potential. In Figure 1d, red line shows the cyclic voltammetry result obtained for the sensing region without the insulating layer on any working electrode. Green line shows the cyclic voltammetry result with the insulating layer on one working electrode (large ohmic drop one). It can be seen that the working electrode at a distance from the reference electrode produces almost no electrochemical signal, as the two results are very similar. Combining these two experiments, we can conclude that it is practicable to use ohmic drop to separate electrochemical signals.The device enables a high degree of integration and simple sample injection. This study provides a new platform for the field of multiplexed detection. Reference 1. Zhang, Huijie, et al. Analytical chemistry 89.11 (2017): 5832-5839.2. Ino, Kosuke, et al. Electrochemistry Communications 77 (2017): 76-80. Figure 1