Organic field-effect transistor with extended indium tin oxide gate structure for selective pH sensing

In this study, organic field-effect transistors (OFETs) with extended gate structure were fabricated for selective pH sensing applications. Indium tin oxide (ITO) was used as extended gate electrode as well as an active layer for H+ sensing. The threshold voltage of the fabricated ion-selective OFET was varied by the changes in the electrochemical potential at the ITO electrode surface upon its exposure to buffer solutions with variable pH values. The sensor showed excellent linearity and a high sensitivity of 57–59 mV/pH in the pH range of 2–12. The selectivity of the ITO sensing layer to H+ ions was also investigated by measuring the interfering effect of Ca2+ and K+ ions in the buffer pH solutions. The results showed that the Ca2+ and K+ ions weakly interfere with the selective pH sensing of the ITO-extended gate OFET sensor device.

Graphical abstractA bottom-gated OFET structure with extended ITO gate sensing electrode was fabricated for selective pH sensing. The extended gate structure was adopted for insuring the stability of the OFET as a transducer in the electrolyte.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The ITO-extended gate organic ISFET showed pH sensing capability in a range of 2–12 with linearity. ► The device also showed high sensitivity of 57–59 mV/pH and fast response. ► The device could be used for sensing H+ selectively in the electrolyte solutions containing K+ or Ca2+ ions. ► This pH sensor can be potentially used in vitro environments without an ion-selective membrane.