The present report highlights a novel, membrane-free potentiometric sensor for the detection of sodium ions (Na +) in saliva, thus avoiding the limitations associated with the existing technology, which includes ionophore leakage through the membrane and the high cost of manufacturing. The effective combination of sol-gel synthesized MnO 2 nanoparticles with laser-induced graphene (LIG). The LIG was prepared by direct laser scribing on polyimide. In contrast to conventional sensors, where a liquid membrane is used, this device incorporates an adsorption reaction using Na + intercalation into MnO 2 nanocomposites. The sensor optimization was achieved by employing preconditioning at -1 V for 100 seconds. This considerably improved electroactivity on the electrode surface. The linear range of detection of the sensor lies between 25 μM and 5 mM, while its limit of detection is 4. 23 μM and its response slope is 10. 63 ± 0. 15 mV/decade. Real-sample tests in both saliva and serum showed excellent agreement with standard ion-selective electrode (ISE) measurements (R 2 = 0. 9917, p > 0. 05) with negligible interferences from physiologically relevant ions, such as K +, Ca 2+, and Mg 2+. In addition, this sensor demonstrates long-term operational stability over one month, with a relative standard deviation (RSD) of 4. 21%, confirming its reliability for clinical applications. This drop-and-sense platform combined the merits of cost-effectiveness (∼ 0. 09), ease of operation, and high analytical performance, hence offering a promising point-of-care tool for non-invasive healthcare applications. • MnO 2 -LIG sensor allows for non-invasive salivary Na + detection • A membrane-free design has high selectivity and a fast 100 s response • Detection limit of 4. 23 μM with linearity from 25 μM–5 mM (R 2 = 0. 9917) • Stable, reproducible, and interference-free Na + measurement in saliva • Drop Sense type affordable platform for real-time personalized Na + tracking
Patra et al. (Fri,) studied this question.