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Liquid transistor connects fluids with electronics

发布时间:2019-03-01 09:12:01来源:未知点击:

By Belle Dumé The first ever liquid transistor has been made by researchers in the US. The revolutionary device, which works thanks to an “electrowetting” effect between two competing fluids, could find applications in biotechnology and in the rapidly developing world of flat panel displays. One of the limitations of current microfluid devices is in the sophistication needed to convert information conveyed by the movement of a fluid into an electronic signal, so that it can be processed by a computer. Signals are typically converted through optical sensing – using a video camera or by exciting fluorescent dyes already present in a fluid. These approaches are time consuming, expensive and confer only limited information. Now Andrew Steckl and Duk-Young Kim at the University of Cincinnati, US, have come up with an alternative – a liquid version of the electronic field-effect transistor (FET). An electronic FET uses an electric field to control the flow of current between two points known as the source and the drain. The so-called “LiquiFET” is similar to an electronic FET but operates using liquids, and could therefore transmit information from a liquid device directly into conventional electronic signals. The shape of a liquid droplet placed on a hydrophobic (water-repellent) surface can be changed by applying a voltage across the surface – a trick known as “electrowetting”. The LiquiFET works thanks to a competitive electrowetting effect between water and another fluid, like oil, placed on the same surface. Steckl and Kim made their LiquiFET by first placing a dielectric insulating layer between two electrodes. Next, the researchers coated the top electrode with a hydrophobic material. Then they placed a water droplet – containing potassium chloride for conduction purposes – and an oil droplet on top of the structure. With no applied voltage, the oil layer settles in between the water layer and the hydrophobic surface because of the surface tension between the two liquids. Under this condition, the oil prevents any current from flowing between source and drain and the transistor is switched off. However, when the researchers apply a voltage to the water droplet, this pushes the oil layer away and water touches the hydrophobic surface. Current then flows between the source and the drain, switching the transistor on. Moreover, the current increases as the voltage applied to the gate increase, as in a conventional FET. “LiquiFETs have great potential for large-area electronics as well as in biomedical applications,” Steckl told New Scientist. “They can directly detect, manipulate and analyse liquids, which is not easy for solid state transistors.” “The applications also range from the macro to nano-scale in flat panel displays, microelectronics and drug delivery,” he adds. The Cincinnati researchers’ plan is to improve the electrical characteristics of the device and to use it to connect a microfluid device to an electronic circuit. Journal reference: