Touchscreens are ubiquitous devices found in all manner of objects we commonly use today, from smartphones to screens inside vehicles. Researchers at the University of Cambridge have demonstrated a new technique that shows how a typical touchscreen could identify common ionic contaminants found in soil or drinking water. The process will require a drop of liquid sample to be placed on the screen.
The sensitivity of the touchscreen sensor is comparable to typical lab-based equipment, which could make the new process useful in settings where resources are limited. Currently, the researchers have created a proof of concept and say that it could one day be expended for a wide range of sensing applications possible expended sensing applications include biosensing or medical diagnostics.
Typical smartphone touchscreens are covered in a grid of electrodes, and when the finger disrupts the local electrical field of the electrodes, the phone interprets the signal. The team used the computational power of smartphone sensing applications that don’t require the camera, peripheral devices, or significant changes to the screen.
The project started with computer simulations that were then validated using a stripped-down, standalone touchscreen similar to those used in phones and tablets. In their experiments, researchers placed different liquids under the screen to measure the change in capacitance and recorded the measurements from each droplet using standard touchscreen testing software. Ions in the fluid interact with the screen’s electrical fields differently, depending on the concentration of ions in their charge.
Simulations showed where the electric field interacts with the fluid droplet. The experiment showed a linear trend for a range of electrolytes measured on the touchscreen. The sensor saturates at an anion concentration around 500 micromolar, correlated to the conductivity measured alongside. The team says the detection window is ideal for sensing ionic contamination in drinking water. The research is a starting point for a broader investigation into the use of touchscreen sensing and mobile technologies and creating tools accessible to everyone for rapid management and communication of data.