A paper based, all organic, reference-electrode-free ion sensing platform

We present a reference-electrode free, all organic K⁺ sensitive ion sensing platform fabricated by simplest means on a plain sheet of paper. This platform is based on two identical ion selective electrodes (ISEs) which are assembled by bonding a polymeric ion selective membrane (ISM) directly onto a drop-casted PEDOT:PSS electrode. Taking full advantage of the so called pulsetrode concept, a current pulse is used to measure the concentration of the targeted ion. The current forces an ion flux out of the first ISE, through the sample and into the second ISE. This flux leads to a well-defined potential jump at the second ISE, as soon as the target ion locally depletes within the analyte, whereas the current induced potential change at the first ISE does not depend noticeably on the type of background electrolyte. Hence, the potential difference between the ISEs, required to apply the current is directly related to the ion concentration within the sample. This concept allows for a 20-fold sensitivity enhancement compared to classical potentiometric measurements in physiological backgrounds. As mutual potential drifts of the ISEs cancel out, the sensor response showed excellent stability and did not change during multiple measurements over three months.