ELECTRONIC "tongues" could soon be used to monitor the quality control of bottled mineral water. The devices could also sample complex solutions such as blood or urine.

The human tongue can distinguish between a dazzling array of subtle flavours using a combination of just four elements of taste: sweet, sour, salt and bitter. Each element is detected by one of the four types of taste bud located on the tongue. Now researchers at the University of Texas in Austin have designed an electronic tongue that works along the same lines (Journal of the American Chemical Society, vol 120, p 6429).

Using chemical sensors, they have demonstrated that the electronic tongue can "taste" different solutions. The team attached four well-known chemical sensors to minute beads made of polyethylene glycol and polystyrene. The beads were placed in micro-machined wells on a silicon wafer.

The sensors respond to chemical stimuli by changing colour, so the wafer was placed between a light source and an image sensor. The responses were monitored as red, green and blue light channels from each well. The first device they built was designed to detect calcium and cerium ions, acidity and the simple sugars. Each sensor responded differently to the various conditions: for example, one turned yellow in response to high acidity, red if cerium ions were present, and purple under basic conditions.

The sensors responded to different combinations of the four artificial taste elements with unique combinations of red, green and blue, enabling the device to analyse for several different chemical components simultaneously.

Authors - William Wood and Lila Guterman

New Scientist issue 18th July 1998, page 10

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