Chemical Engineering

Touchscreen technology as a powerful sensor

A typical touchscreen could be used to identify common ionic contaminants in soil or drinking water by dropping liquid samples on the screen

September 28, 2021
The Scitech

Researchers from the University of Cambridge have demonstrated how a typical touchscreen could be used to identify common ionic contaminants in soil or drinking water by dropping liquid samples on the screen, the first time this has been achieved. The sensitivity of the touchscreen sensor is comparable to typical lab-based equipment, which would make it useful in low-resource settings. The researchers say their proof of concept could one day be expanded for a wide range of sensing applications, including for biosensing or medical diagnostics, right from the phone in your pocket. The results are reported in the journal Sensors and Actuators B. “We wanted to know if we could interact with the technology in a different way, without having to fundamentally change the screen,” said Dr Ronan Daly from Cambridge’s Institute of Manufacturing, who co-led the research. “Instead of interpreting a signal from your finger, what if we could get a touchscreen to read electrolytes, since these ions also interact with the electric fields?” The researchers started with computer simulations, and then validated their simulations using a stripped down, standalone touchscreen, provided by two UK manufacturers, similar to those used in phones and tablets. The researchers pipetted different liquids onto the screen to measure a change in capacitance and recorded the measurements from each droplet using the standard touchscreen testing software. Ions in the fluids all interact with the screen's electric fields differently depending on the concentration of ions and their charge.

“Our simulations showed where the electric field interacts with the fluid droplet. In our experiments, we then found a linear trend for a range of electrolytes measured on the touchscreen,” said first author Sebastian Horstmann, a PhD candidate at IfM. “The sensor saturates at an anion concentration of around 500 micromolar, which can be correlated to the conductivity measured alongside. This detection window is ideal to sense ionic contamination in drinking water.” One early application for the technology could be to detect arsenic contamination in drinking water.  “In theory, you could add a drop of water to your phone before you drink it, in order to check that it’s safe,” said Daly. At the moment, the sensitivity of phone and tablet screens is tuned for fingers, but the researchers say the sensitivity could be changed in a certain part of the screen by modifying the electrode design in order to be optimised for sensing. While it’s now possible to detect ions using a touchscreen, the researchers hope to further develop the technology so that it can detect a wide range of molecules. This could open up a huge range of potential health applications.

Source: University of Cambridge news release