Fully 3D-printed solid-contact potentiometric sensor for sodium determination

This paper describes the design and fabrication of the first fully 3D-printed (3Dp) solid-contact (SC) ion-selective electrode for use in potentiometric sensing. This sensor, constructed from stereolithographically printed Na⁺-ion-selective membranes and carbon-infused polylactic acid transducers, fabricated via fused-deposition modelling, demonstrates the diversity and extreme utility of 3D-printing in electroanalysis. We demonstrate the ability to manipulate and fine-tune transducer hydrophobicity based on print angle and print thickness, leading to highly stable (∼20 μV drift per hour) 3Dp-Na⁺-ISE. The developed sensor demonstrates a linear and Nernstian response (slope of 57.1 mV/decade) towards Na⁺, covering the physiologically relevant Na⁺ levels found in biological fluids (240 μM-250 mM). The limit of detection and limit of quantification of the developed sensor were determined to be 0.0024 mM and 0.008 mM, respectively. The 3Dp-Na⁺-ISE selectively measures Na⁺ in the presence of common interfering ions (e.g., potassium, ammonium, magnesium, and calcium) found in biological fluids, and the effectiveness of the sensor was confirmed through the successful determination of Na⁺ in human saliva samples. The ability to construct solid-contact potentiometric sensors using entirely 3D printed materials permits the mass-production of highly functional and low-cost sensors with diverse applicability.