Highly selective and robust nanocomposite-based sensors for potassium ions detection

•A systematic study of the effects of incorporating polymer-functionalised silica nanoparticles inside ion sensing films have been conducted for the first time. Such study included an analysis of the ionic diffusion by potentiometric and state-of-the art quartz microbalance, allowing the rational design of highly selective and stable ion sensors, and microindentation for studying the hardness heterogeneity across the surface of the films.•A highly robust sensor, with a mechanical hardness 100 times harder compared to the standard approach based on plasticized PVC was developed, which allowed the integration of the devices in biological applications. The robustness of the devices could be assessed by the development of a low-cost fluidic chamber, fabricated by additive manufacturing techniques. Such chamber could be used to subject the devices to harsh environments by applying a high shear stress to the devices.•The sensors reported in this work showed an extremely low electrochemical noise of 1.2 µV h-1, one of the lowest values ever reported, while maintaining a high selectivity towards potassium. The high selectivity and stability of these devices could then be used for the accurate measurement of potassium ions in simulated body fluids and human serum, being able to quantify when the samples were spiked with 500 µM of K+. Ion-selective electrodes are employed in technological important fields, such as medical diagnosis, or water quality evaluation. Plasticized polymeric membranes containing ionophores are typically used in these devices. However, the low mechanical hardness and limited robustness of these electrodes combined with their low selectivity limit their use in high precision applications. In the present work, PVC-functionalised silica nanoparticles incorporated in a plasticized PVC film have been integrated into ion sensors for the first time applied to the detection of K+ in solution. This approach was used for the design of highly specific and mechanically robust systems using a fluidic chamber. The device presented a hardness in the range of 5.2 GPa, being 2 orders of magnitude higher than the one reported for plasticized PVC (0.059 GPa), and could measure the concentration of K+ with high specificity when compared to Ca2+ and Na+ ions compared to the conventional approach. The interactions of the sensing films with the ions in solution were systematically studied for different degrees of PVC functionalisation to allow the rational design o