3D-printed sensor strips bring lab-quality testing to the field

The solid-contact format of both ion-selective and reference electrodes has contributed to the decentralization of ion sensing in domains such as health, sport and the environment. Nonetheless, the realization of a fully integrated and low-cost potentiometric cell has remained a challenge until now. Accordingly, the novelty of this work relies on the first demonstration of a monolithic full potentiometric cell fabricated with 3D printing technology (3DP-PC), specifically, using fused filament fabrication (FFF). Both the ion-selective and reference electrodes are integrated into a monolithic disposable device with minimal postprocessing. The design flexibility of FFF enables the incorporation of an in-built sample well, which allows for independent electrode conditioning and direct analysis of liquid samples by simply adding 1.5 mL of the sample solution. The 3DP-PC exhibited a linear potentiometric response toward potassium ion in the 10–5–10–1 M range, with a slope of 56.4 ± 1.1 mV decade–1 (n = 3), limit of detection of ca. 10–6 M, and good potential reproducibility (ESD0 = ± 4 mV, n = 3). Notably, no water layer formation was observed; short-term drift was 115 ± 57 μV h–1 and long-term potential drift was −419 ± 66 μV h–1 over 72 h. The device enabled reliable detection of the potassium ion in artificial interstitial fluid and sweat samples, showing recoveries close to 100%. These results represent the initial milestone toward a completely 3D printed solid-contact potentiometric cell, incorporating all sensing elements (indicator and reference). By eliminating the need for complex manufacturing and multistep assembly, we anticipate a paradigm shift in the on-demand and decentralized production of potentiometric sensing platforms.