Investigation of a surface decorated Ag-MnO2@MGCN nanointerface towards membrane-free electrochemical Na+ ion sensing in sweat.

Noninvasive continuous electrolyte monitoring, including Na+ ion levels in sweat, is essential for real-time physiological assessment. The changes in sweat Na+ ion levels reflect underlying physiological conditions and might be used as a potential biomarker for electrolyte imbalances. In this work, we report an electrochemical Na+ ion switch based on a surface-anchored Ag-MnO2@mesoporous graphitic carbon nitride (MGCN) nanointerface. The results of morphological analysis revealed a hierarchical architecture consisting of MnO2 nanorods uniformly anchored to MGCN nanosheets and decorated with Ag nanoparticles that form a highly conductive and electroactive platform. Electrochemical analysis showed distinct oxidation and reduction peaks at 0.25 V and 0.08 V, respectively, indicating strong redox activity and efficient charge transfer upon interaction with Na+ ions. The Ag-MnO2@MGCN sensor showed a broad linear range from 0.1 to 150 mM, with a LOD of 0.06 mM, and a sensitivity of 9.62 µA mM-1 cm-2. The sensor also demonstrated excellent repeatability, stability and high recovery values ranging from 96.46% to 101.2% in artificial sweat samples, confirming its analytical reliability. The sensing mechanism is explained via the intercalation-deintercalation behaviour of Na+ ions within the MnO2 framework of Ag-MnO2@MGCN, while Ag nanoparticles and MGCN synergistically enhance charge transfer. These findings demonstrate the potential of the developed Ag-MnO2@MGCN nanointerface for the future development of membrane-free electrochemical sensors for Na+ detection in sweat.