Microfluidic ion-responsive channels based on electrowetting

Abstract

Abstract In this work, autonomously functioning artificial ion channels were fabricated and assessed. An electrowetting-based valve was formed in a constricted region surrounded by poly(dimethylsiloxane) walls with a gold electrode at the base. The gold electrode was connected to an integrated hydrogen electrode to detect the pH of a solution to be transported. A mixed potential was generated when the gold valve electrode and a platinum black electrode in the hydrogen electrode were connected by the solution, which polarized the gold electrode. As a result, the gold electrode became sufficiently hydrophilic at pH values above a certain threshold, and the solution was able to pass through the valve region. The threshold potential could be adjusted by changing the width of the valve. To expand the range of application to biomolecules, a urea-responsive valve was also fabricated by immobilizing the enzyme urease on the platinum black electrode. Moreover, passage of the solution through the valve was coupled with the transportation of a second solution through a separate flow channel, using a composite electrode consisting of a gold electrode used to form the electrowetting-based valve and a zinc electrode to detect the arrival of a solution.