Integrated Headband for Monitoring Chloride Anions in Sweat Using Developed Flexible Patches

Flexible wearable potentiometric ion sensors for continuous monitoring of electrolyte cations have made significant advances in bioanalysis for personal healthcare and diagnostics. However, less attention is paid to the most abundant extracellular anion, chloride ion (Cl^-) as a mark of electrolyte imbalance and an important diagnostic indicator of cystic fibrosis, which has important significance for accurate monitoring in complex biological fluids. An all-solid-state Cl^--selective electrode is constructed utilizing oxygen vacancies reinforced vanadium oxide with a nitrogen-doped carbon shield as the solid contact (V₂O_3-@NC/Cl^--ISE). The prepared V₂O_3-@NC/Cl^--ISE exhibits a low detection limit of 10^-5.45 M without an interfacial water layer and shows a highly stable potential with 7.24 μV/h during 24 h, which is attributed to the rapid interfacial electron transfer of the conductive carbon layers and the valence state transition of the polyvalent vanadium center in charge storage processes. Additionally, the custom flexible sensing patch presents an excellent sensitivity retention rate under bending (95%) and twisting (93%) strains and possesses good anti-interference performance (ΔE < 8 mV) against common interfering ions and organic substances in sweat. Real-time monitoring of the Cl^- concentration in sweat aligns with ion chromatography analysis results. This study presents a compact wearable Cl^- monitoring platform for the easy tracking of exercise-induced dehydration and cystic fibrosis screening with promising applications in smart healthcare.