Electrical Textile Valves for Paper Microfluidics

Abstract

This paper describes electrically activated fluidic valves that operate based on electrowetting through textiles. The valves are fabricated from electrically conductive, insulated, hydrophobic textiles, but the concept could be extended to other porous materials. When the valve is closed, the liquid cannot pass through the hydrophobic textile. Upon application of a potential (in the range of 100 -1000 Volts) between the textile and the liquid, the valve opens and the liquid penetrates the valve. These valves actuate in less than 1 second, require low energy (~27 µJ per actuation), and work with a variety of aqueous solutions, including low surface tension aqueous liquids, and bioanalytes. They are bistable in function, and are in a sense, the electrofluidic analog of thyristors. They can be integrated into paper microfluidic devices to make circuits that are capable of liquid control, including autonomous fluidic timers, and fluidic logic. 2Paper microfluidics is a technology particularly well-suited for uses in public health, point of care diagnostics for resource-limited settings, veterinary medicine, food and water quality testing, and environmental monitoring. [1], [2], [3], [4], [5], [6], [7], [8] Many common assays require the addition of multiple reagents and multiple washing steps, where the timing of each step influences the outcome of the assay. For example, paper-based devices for ELISA [9,10], [11], [12] , electrochemiluminescence (ECL) [13] , or DNA detection [14], [15] , require multiple individually timed steps of binding, washing and amplification. Performing these steps manually is labor intensive (a single assay may take from several minutes to hours) and prone to human errors. Fully automated paper-based assays have the potential to be faster and more accurate than those requiring human operations.The most important component required for autonomous assays is a fluidic valve that gates the flow of liquids with timed actuation. Different methods of valving have been explored for paper devices [16], [17], [18], [19], [20], [21], [22], [23] , which operate either by changing the wicking properties of the paper or by mechanically altering connectivity between the channels.Wicking speed in the paper is determined by three parameters: The hydrophilicity of its surface, the size of the pores, and the viscosity of the liquid. These parameters can be altered to actuate flow of liquids. For example, hydrophobic surfaces can be rendered hydrophilic by an electrical plasma [16] or by electrochemical [17,24] or ultraviolet modification. [25] Surfactants can also be used to assist liquids in crossing the hydrophobic barriers [23,26,27] ; dissolved polymers [28] or sugars [29] can increase the viscosity of the liquids and limit the flow.Mechanical motion of paper has also been used for actuating the flow of liquids in paper. Electromagnetic [18] , hygroexpanding [19], [30] manually operated push-buttons [20] , flaps [21] , pop-up [31] , folding [10], [32] and sliding strip [14] concepts for valving h...

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