Paper-based potentiometric ion sensors constructed on ink-jet printed gold electrodes

Printed electrodes on a recyclable low-cost coated paper were used as a platform for constructing potentiometric ion sensors consisting of an ion-selective electrode (ISE) and a reference electrode (RE). The reference and working electrodes were printed by using a stable suspension of gold nanoparticles (AuNP) as the ink. Sintering turned the printed electrodes conductive. A poly(3,4-ethylenedioxythiophene) (PEDOT) layer, with poly(styrene sulfonate) (PSS) ions as counterions was deposited on the gold electrodes by electropolymerization, drop-casting or ink-jet printing. The reference electrode was prepared by further coating the PEDOT(PSS) layer with a poly(vinyl chloride) (PVC) membrane containing a lipophilic salt, tetrabutylammonium tetrabutylborate (TBA-TBB), thus resulting in a solid-contact reference electrode (SCRE). The working electrode was modified by coating the PEDOT(PSS) layer with a K+-selective membrane, to obtain a solid-contact K+-ISE. The electrochemical characteristics of the resulting electrode systems were studied by amperometric, potentiometric and electrochemical impedance spectroscopic (EIS) measurements. The potentiometric response toward K+ ions was additionally studied. The surface structure of the PEDOT(PSS) layers deposited by the different methods was studied with atomic force microscopic (AFM) measurements. It was shown that a well-functioning planar electrode platform with good electrochemical characteristics could be prepared by ink-jet printing in a repeatable manner. The planar electrode platform presented here offers a user-friendly and ecological alternative to perform chemical analysis from small sample volumes.