Yanming Xia and co-workers at ETH Zürich, the Chinese Academy of Science, and Xiamen University have recently reported the integration of a new type of adjustable valve within centrifugal microfluidic systems.
The electrowetting centrifugal (EWC) valve operates in a similar way to a burst valve, in which fluid flow is allowed above a certain pressure, but allows the magnitude of the “burst pressure” to be varied during use. As with traditional burst valves, the EWC valve uses a hydrophobic surface coating to contain liquid via control of surface energy. However, the EWC surface hydrophobicity can be varied during operation by application of a voltage. This feature allows the precise control of fluid flow during centrifugal experimentation.
To demonstrate the valve’s utility, the authors performed detection and analysis of CD4 human immune cells via a bead-based fluorescence-linked immunosorbent assay. In this assay, three separate EWC valves were used to control reagent flow into the reaction chamber. First, magnetic beads and human CD4 antigen were released into the reaction chamber and allowed to incubate for 60 minutes. Then, a fluorophore-linked antibody was delivered into the reaction chamber. The reaction mixture was finally incubated for another 60 minutes to perform a sandwich immunoassay and quantify CD4 human immune cell antigen concentrations down to 0.04 mg/mL.
This work greatly enhances the operational and configurational flexibility of centrifugal microfluidic workflows, with a range of complex fluid manipulations being controlled in a wireless manner.
A centrifugal microfluidic platform integrating electrowetting valves. (a) Schematic of the entire centrifugal platform. (b) Fluid under a certain centrifugal pressure is held within a narrow channel in the burst valve. (c) Fluid transport through the narrow channel due to centrifugal pressure and the application of an electric field. (d) Top view image of a centrifugal microfluidic chip containing 12 EWC valves. (e) Detailed image of an EWC valve.
The full paper can be found here.