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Hidden ability of smartphone touchscreens

The touch screen technology used in millions of smartphones and tablets could also be used as a powerful substance sensor, without the need for any modifications.

Ronan Daly’s team from the University of Cambridge in the UK has demonstrated how a typical touch screen can be used to identify common ionic contaminants in soil or drinking water, by dropping samples, even liquid ones, onto the screen. . This is the first time this has been achieved. The sensitivity of the touch screen sensor is comparable to that of typical laboratory devices, which would make such screens very useful in scenarios with little availability of technical resources.

The researchers say that detection using this kind of touch screen technology could one day be extended to a wide range of applications, including biosensing or medical diagnostics, and the operation would be done directly from the phone.

Touchscreen technology is ubiquitous in our everyday lives: a typical smartphone screen is covered by a grid of electrodes, and when a finger interrupts the local electric field of these electrodes, the phone interprets the signal.

Other research teams have used the computing power of a smartphone for sensing applications, but these have relied on the camera or peripheral devices, or have required major changes to the screen.

“We wanted to know if we could interact with the technology in a different way, without having to change the screen,” explains Daly. “Instead of interpreting a finger signal, what if we could make a touch screen read the electrolytes, since these ions also interact with electric fields?”

The researchers set out to answer that question. They started with computer simulations, and then validated their simulations using a separate touch screen, stripped of much of the phone, provided by two British manufacturers. This screen is similar to those used on phones and tablets.

The researchers pipetted droplets of different liquids onto the screen to measure a change in capacitance and recorded the measurements of each droplet using standard touchscreen testing software. All ions in fluids interact with the electric fields on the screen differently depending on the ion concentration and charge.

The touchscreen technology used in millions of smartphones and tablets could also be used as a powerful sensor, without the need for any modifications. (Image: University of Cambridge)

One of the first applications of this reuse of technology could be the detection of arsenic contamination in drinking water. In some parts of the world without water treatment plants, arsenic contamination is a serious problem. “In theory, you could add a drop of water to your phone before drinking it to check that it’s safe,” says Daly.

Daly’s team details their experiments in the academic journal Sensors and Actuators B under the title “Capacitive touchscreen sensing – A measure of electrolyte conductivity”. (Source: NCYT from Amazings)

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