Ultrasensitive transistor detects herbicide in water
A new polymer-based, solid-state transistor can more sensitively detect a weed killer in drinking water than existing hydrogel-based fluorescence sensor chips, according to a study published in Chemistry — A European Journal. The organic thin-film transistor is based on semiconducting molecules of carboxylate-functionalised polythiophene (P3CPT) and, unlike other conjugated polymer-based sensors, is a solid-state device that can conduct an electric current when placed inside a fluid.
The device, designed by Tsuyoshi Minami of The University of Tokyo’s Institute of Industrial Science and colleagues, works by adding copper ions, which bind to the P3CPT molecules. When the device is placed in water that contains even a small amount of the agricultural herbicide glyphosate — whose presence in drinking water may be harmful to human health — the copper ions leave the P3CPT molecules to attach to the glyphosate molecules. This causes a detectable reduction in the flow of electric current through the device.
The scientists found that the device was so sensitive that it could detect as low as 0.26 ppm of glyphosate in drinking water. The team compared their new device to a conventional fluorescence sensor chip, which was only capable of detecting down to 0.95 ppm of glyphosate. To put this into perspective, the maximum allowable amount of glyphosate in drinking water, according to the United States Environmental Protection Agency, is 0.7 ppm.
The scientists believe that the sensitivity of their device boils down to interactions occurring within individual polymer molecules and between neighbouring ones. Commonly used fluorescence sensors depend solely on interactions occurring within individual molecules.
“Our device could be a novel solid-state platform for sensing target molecules in aqueous media,” Minami said. The researchers are currently working on further developing their polythiophene-based sensors.
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