A flexible graphene-printed sensing platform for real-time multi-analyte detection of pH, sodium, and potassium

Flexible point-of-care testing (PoCT) with simultaneous, real-time biomarker monitoring is essential for next-generation wearable health platforms. Here, we present a graphene-printed electrolyte-gated field-effect transistor (EG-GFET) sensing platform fabricated on a flexible polyimide PCB substrate for multiplexed detection of pH, sodium (Na⁺), and potassium (K⁺). Graphene ink synthesised via liquid-phase exfoliation was spray-coated to form the active transistor channel. Optimised EG-GFET sensors achieved a pH sensitivity of 25.77 ± 1.42 mV/pH (shift of Dirac point) and 61.59 ± 3.17 μA/pH (modulation of drain current). Ion-selective membranes enabled selective Na⁺ and K⁺ sensing with sensitivities of - 61.28 ± 2.95 mV/log₁₀ [Na⁺] and - 56.09 ± 3.28 mV/log₁₀ [K⁺], respectively, over linear concentration ranges of 50 μM - 350 mM for Na⁺ and 50 μM - 150 mM for K⁺. The flexible devices maintained stable operation under bending angles up to 120°. Real-time dual-analyte experiments further demonstrated simultaneous pH/Na⁺ and pH/K⁺ monitoring with minimal observable cross-interference. The platform was further evaluated in acidic and alkaline artificial sweat for pH, Na⁺, and K⁺ sensing. These results establish a flexible printed EG-GFET platform for pH and electrolyte sensing in buffer solutions and selected artificial-biofluid matrices.