Ag-MXene conductive ink-based highly sensitive, screen-printed sweat sensor with multi-ions detection

Highly conductive and flexible inks are crucial for the fabrication of next-generation wearable electrochemical sensors. This study presents a multi-ion sweat sensor composed of screen-printed Ag-MXene conductive ink, featuring a high electrical conductivity of 2 × 10⁶ S m^-1. A novel electrode configuration was developed, comprising three working electrodes (WEs) together with a common reference (RE) and counter electrode (CE), all coated with the same ion-selective gel. The use of a uniform gel across all WEs ensures a consistent sensing environment, minimizes ion cross-talk, and improves repeatability. The Ag-MXene ink has excellent electrochemical activity, resulting in rapid, reproducible, and very selective potentiometric responses even at low ion concentrations. The Ag-MXene ink-based multi-ion sweat sensor achieved near-Nernstian sensitivities of 65.1 ± 0.7 mV/decade for Na⁺, 59.8 ± 0.6 mV/decade for K⁺, and 57.5 ± 0.8 mV/decade for Li⁺. These results are close to the theoretical Nernstian slope (∼59.2 mV/decade at 25 °C). On-body testing reveals that the sensor performs consistently under mechanical deformation and in real-world situations, demonstrating its viability for continuous health monitoring. After mechanical cycling, the Ag–MXene electrodes retained R/R₀ ≈1 with negligible hysteresis, demonstrating the structural and electrical integrity of the composite ink. Sensing cycling further verified stability: repeated stepwise measurements for Na ⁺ (5–160 mM), K ⁺ (1–32 mM), and Li ⁺ (1–100 mM) produced nearly identical potential peaks across successive cycles with no cumulative drift and minimal up/down hysteresis. The calibrations remained near-Nernstian, with response times of ∼2–3 s and sub-second recoveries, demonstrating excellent mechanical and electrochemical durability. The scalable screen-printing fabrication approach enables the cost-effective and reliable fabrication of flexible, wearable multi-ion sensors. This study demonstrates the potential of Ag-MXene-based electrodes for high-performance, multi-functional sweat sensing and offers a feasible path to enhance wearable electronic technologies.