Spectroelectrochemical Evidence of Interconnected Charge and Ion Transfer in Ultrathin Membranes Modulated by a Redox Conducting Polymer,
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We present spectroelectrochemical sensing of the potassium ion (K+) at three very distinct analytical ranges─nanomolar, micromolar, and millimolar─when using the same ion-selective electrode (ISE) but interrogated under various regimes. The ISE is conceived in the all-solid-state format: an ITO glass modified with the conducting polymer poly(3-octylethiophene) (POT) and an ultrathin potassium-selective membrane. The experimental setup is designed to apply a potential in a three-electrode electrochemical cell with the ISE as the working electrode, while dynamic spectral changes in the POT film are simultaneously registered. The POT film is gradually oxidized to POT+, and this process is ultimately linked to K+ transfer at the membrane-sample interface, attending to electroneutrality requirements. The spectroelectrochemistry experiment provides two signals: a voltammetric peak and a transient absorbance response, with the latter of special interest because of its correspondence with the ...