Capacitive touchscreen sensing - A measure of electrolyte conductivity

•Exploration of a new format with sensing directly from fluid drops on a touchscreen.•Simulations are combined with experiments to reveal the working principles.•Suitable detection window for sensing drinking water contamination and soil health.•Measurement possible across protective layer, for use in mobile technologies. Mobile technologies such as smartphones and tablets combine computational power with inbuilt sensors and networking capabilities, making them ideal measurement instruments. There is already a rich history of research and commercially manufactured accessories taking advantage of their sensing and data visualisation capabilities. However, to-date the touchscreen component has not yet been translated to the widely established fields of capacitance-based bio- and environmental sensing. Here, we demonstrate the concept of contactless conductivity sensing of fluid samples placed directly on top of a projected mutual capacitive touchscreen with the measurement of a variety of electrolytes, leveraging the touchscreen’s multi-touch capabilities. Electrolyte ions are particularly susceptible to the electric fringe field induced by capacitive touchscreens, and we report here a near-linear response to the ionic concentration of metal cations interesting for drinking water quality and soil health monitoring across a range of 0–500 μM (up to 100 μS). Simulation results are compared with experimental findings to reveal both the working principles and the key parameters that will be important for future sensing applications. This sensor demonstration is a starting point for broader exploration of the use of projected touchscreen sensing in mobile technologies and the creation of tools that are accessible to everyone, allowing rapid measurements and communication of data.