Bipolar electrodes (BPEs) with arrays of cathodic and anodic poles were developed for use in closed bipolar systems. To increase the number of BPEs in the array, the anodic and cathodic poles were connected with each other using thin leads. A further increase in the number of BPEs was achieved by forming the cathodic and anodic poles of the BPEs and the leads in different layers. A device with 9 × 10 arrays of cathodes and anodes was thus realized. When using this device to sense hydrogen peroxide (H₂O₂), the sensitivity and linear range of calibration plots could be adjusted by changing the driving voltage and the area ratio between the cathodic and anodic poles. The devices were used to image H₂O₂ and obtain time-lapse images for the diffusion and dilution of H₂O₂. Furthermore, DNA detection was demonstrated using an electroactive intercalator. The sensitivity could be improved by making the anodic poles smaller with respect to the cathodic pole and concentrating the electrochemiluminescence (ECL) in a small area. The ECL intensity changed according to the target DNA concentration in the solution.

Electrochemical application has been widely used in the study of biosensors. Small biomolecules need a sensitive sensor, as the transducer that can relay the signal produced by biomolecule interactions. Therefore, we are improvising a sensor electrode to enhance electrochemical conductivity for the detection of small DNA molecule interaction. This work describes the enhanced electrochemical conductivity studies of copper nanowires/gold nanoparticles (CuNWs/AuNPs), using the screen-printed gold electrode (SPGE). The AuNPs were synthesized using the Turkevich method as well as characterized by the high-resolution transmission electron microscopy (HRTEM) and ultraviolet-visible (UV-Vis) analysis for the particle size and absorption nature, respectively. Further, the surface morphology and elemental analysis of a series of combinations of different ratios of CuNWs-AuNPs-modified SPGE were analyzed by field emission scanning electron microscopy (FESEM) combined with an energy dispersive X-ray (EDX). The results indicate that the nanocomposites of CuNWs-AuNPs have been randomly distributed and compacted on the surface of SPGE, with AuNPs filling the pores of CuNWs, thereby enhancing its electrochemical conductivity. The cyclic voltammetry (CV) method was used for the evaluation of SPGE performance, while the characterization of the electrochemical conductivity of the electrode modified with various concentrations of AuNPs, CuNWs, and different volumes of dithiopropionic acid (DTPA) has been conducted. Of the various parameters tested, the SPGE modified with a mixture of 5 mg/mL CuNWs and 0.25 mM AuNPs exhibited an efficient electrochemical conductivity of 20.3 µA. The effective surface area for the CuNWs-AuNPs-modified SPGE was enhanced by 2.3-fold compared with the unmodified SPGE, thereby conforming the presence of a large active biomolecule interaction area and enhanced electrochemical activity on the electrode surface, thus make it promising for biosensor application.

Various miniature Clark-type oxygen electrodes (COEs), which are typically used to measure dissolved oxygen (DO) concentration in cellular respiration, have been developed since the 1980s. Arrays with individually addressable electrodes that constitute the sensor were used for various applications. However, the large number of leads and contact pads required for connecting the electrodes and the external instrument complicate the electrode layout and make the operation of integrated COE arrays challenging. Here, we fabricated closed bipolar electrochemical systems comprising 6 × 8 and 4 × 4 arrays of COEs for imaging and multiplexed detection. The cathodic compartment was sealed with a hydrophobic oxygen-permeable membrane to separate the internal electrolyte solution from the sample solutions. Using the bipolar Clark-type oxygen electrode (BCOE) arrays and electrochemiluminescence (ECL), we measured the DO concentration at each cathode. The results revealed that the ECL intensity changed linearly with the DO concentration. In addition, we used ECL imaging to investigate the respiratory activity of Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) in suspensions with different cell densities. The ECL images showed that the ECL intensity changed noticeably with the bacterial density. The bacterial respiratory activity was then qualitatively analyzed based on the ECL images acquired successively over a time duration. Further, we measured the antibiotic efficacy of piperacillin, oxacillin, gentamicin, and cefmetazole against E. coli and P. aeruginosa using the BCOE. We found that the ECL intensity increased with the antibiotic concentration, thus indicating the suppression of the bacterial respiratory activity.

Potential difference at a bipolar electrode (BPE)/solution interface was controlled by forming a polymeric Na ion-selective membrane (ISM) on one part of the BPE. Using the difference between the potentials at the solution/cathodic pole and solution/anodic pole interfaces along with a predetermined driving voltage, the potential differences at the cathodic/anodic pole interface were independently regulated. For open bipolar systems, distinct changes in the intensity of electrochemiluminescence (ECL) were observed by varying the location of the ISM and/or the concentrations of the primary ions determining the potential of the ISM. Folded BPE structures with ISMs at one or both ends of the BPEs were more effective in changing the potential differences at the cathodic/anodic pole interface over a wider range. Furthermore, the potential control was efficient and changes in the ECL intensity were more significant in closed bipolar systems. The device was used for measuring analyte concentration by optimizing the size of the cathodic pole employed for detection and adjusting the driving voltage. We believe that the technique can be a starting point to achieve bipolar electrochemical devices with better controllabilities than those of previous bipolar electrochemical systems and similar reliabilities as those of three-electrode systems.

An electrochemical circuit containing a control unit is used to control the interfacial potential difference between the bipolar electrodes (BPEs) and the electrolyte solution in an open bipolar system. The control unit consists of a polymeric Na+ ion-selective electrode (ISE) connected to a BPE and an Ag/AgCl wire, which connects the electrolyte solution in the control unit to the main chamber via the BPEs. The BPEs contain openings with exposed platinum areas, which serve as cathodic and anodic poles and a potential-determining element. The interfacial potential difference between the potential-determining opening (PDO) and the electrolyte solution can be determined by applying Kirchhoff's second law to the closed circuit containing the PDO, ISE, and Ag/AgCl wire. In the open bipolar system, the intensity of the electrochemiluminescence signal measured for analysis varies depending on the position of the opening of the BPEs. The results suggest that the interfacial potential difference between the anodic and cathodic poles can be varied with a control unit by avoiding ionic crosstalk.