Coulometric Response of H+-Selective Solid-Contact Ion-Selective Electrodes and Its Application in Flexible Sensors†

The analytical performance of H⁺-selective solid-contact ion-selective electrodes (SCISEs) based on solid contact polyaniline doped with chloride (PANI(Cl)) and poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT(PSS)) was characterized by a developed coulometric signal transduction method. PEDOT(PSS) solid contact is covered by PVC based H⁺-selective membrane. The obtained coulometric signal demonstrates that the cumulated charge can be amplified by increasing the capacitance of solid contact. SCISEs covered with spin-coated membrane behave faster amperometric response than electrodes with drop-cast membrane. In contrast to earlier works, the amperometric response and impedance spectrum demonstrates H⁺ transfer through SCISEs is independent from the thickness of membrane. The exceptional behavior of PANI(Cl) H⁺-SCISEs shows that the capacitance estimated from impedance spectrum at low frequency 10 mHz and coulometric signal of PANI(Cl) based SCISEs is influenced by the applied potentials, whereas PEDOT(PSS) solid contact is independent from the chosen applied potentials. Furthermore, preliminary investigations of coulometric signal transduction on flexible pH sensor implies its potential applications in wearable sensors for sweat ion concentration detection.