[Show abstract][Hide abstract]ABSTRACT: Autonomous control of the transport of solutions in microfabricated flow channels using electrowetting-based valves and integrated electrochemical cells is proposed. An electrowetting-based valve formed with a gold electrode was opened when an electrolyte solution reached a zinc electrode in a controlling flow channel and a potential was applied to the gold electrode, causing the transport of the solution in the flow channel. Independent composite electrodes consisting of gold and zinc could function in the same manner without requiring additional electrodes. Controlled autonomous transport of solutions in a network of flow channels could also be carried out using the integrated valves.
[Show abstract][Hide abstract]ABSTRACT: A concept and a device for automatic handling of solutions using an electrochemical cell integrated in a microflow channel are proposed. An electrowetting-based valve was formed in a flow channel of poly(dimethylsiloxane) (PDMS) to separate two solutions in a mixing area. Another flow channel with a cell was formed to transport an electrolyte solution and activate the cell. Since the cell was electrically connected to the valve, the valve opened when the electrolyte solution reached the cell and activated it. To demonstrate the applicability to chemical analyses, a solution containing glucose, and another solution containing glucose oxidase (GOD), horseradish peroxidase (HRP), and amplex red were mixed by the automatic operation, and the enzymatic reactions were allowed to proceed. Fluorometric detection of a product (resorufin) showed clear relation between the fluorescence intensity and the concentration of glucose.
[Show abstract][Hide abstract]ABSTRACT: The possibility to develop a microanalysis system for the acquisition of gastrointestinal information is presented here. The system consists of four assay sites for trypsin, pepsin, and other biochemical compounds. The major components in each assay site were a p H -responsive valve, a p H -stat used to maintain the p H of the solution to be analyzed and used for electrochemical p H -titration, and a freeze-dried enzyme substrate stored in the p H -stat. The operation of the valve is based on electrowetting, and the valve is made p H -responsive by means of a nonstandard three-electrode system. The sample solution was automatically injected into the compartment and rapidly dissolved into the substrate layer. The automatic p H -stat, based on another nonstandard use of the electrochemical three-electrode system, maintained the solution p H and, at the same time, conducted p H -titration. The determination of the activity of the proteases was conducted at their optimum p Hs . The output current showed a clear dependence on the activity of the enzymes. Integrating the functions provides significant advantages for the use of this system as an isolated telemetric microsystem that may operate with wireless signal transmission using a small power supply.
[Show abstract][Hide abstract]ABSTRACT: An electrowetting-based pH-responsive valve that uses a nonstandard electrochemical three-electrode system is proposed. The system comprises a gold valve electrode and an iridium electrode that act as the working and auxiliary electrodes, depending on the purpose, while an iridium oxide pH-sensitive electrode acts as the reference electrode. To make the valve open at pH higher than a threshold, the gold valve electrode is used as the working electrode and a voltage is applied to it with respect to the pH-sensitive reference electrode. To make the valve open at pH lower than the threshold, the gold valve electrode is used as the auxiliary electrode, while the iridium electrode is used as the working electrode. The wettability of the valve electrode is altered when a voltage is applied to it. When the pH of a solution crosses the threshold, the potential of the gold valve electrode exceeds a threshold potential because of the change in the potential of the pH-sensitive reference electrode. Consequently, the gold valve electrode becomes more hydrophilic, thereby allowing the solution to pass through the valve. Furthermore, by combining two valve electrodes, we realized a pH filter that allows solutions with pH within a limited range to pass through it. Urea- and glucose-responsive valves that opened at concentrations higher than the threshold could also be formed by immobilizing an enzyme on the pH-sensitive reference electrode.
[Show abstract][Hide abstract]ABSTRACT: To realize automatic sampling of a solution sensing the pH, a pH-responsive valve that operates using a nonstandard electrochemical three-electrode system was fabricated. A pH-sensitive electrode was used as a reference electrode, and a working electrode or an auxiliary electrode was used as a valve electrode depending on the direction of the pH change. The potential of the reference electrode changed with the increase or decrease of the pH, resulting in a change in the wettability of the valve electrode. By adjusting the voltage applied to the working electrode, the valve opened at pHs higher or lower than a threshold value. By combining two types of valves that opened in the acidic and basic regions, a pH filter that passed only a solution of a limited pH range could also be realized. Furthermore, the pH-responsive valve could also be used to form valves that sensed biochemical molecules and opened at concentrations higher than a threshold.