Technological watch

Inserting an ion exchange gel between the hydrophobic polymer active layer of an organic transistor and the aqueous electrolyte enables volumetric doping of the active layer and operation as an organic electrochemical transistor, rather than as an electrolyte?gated organic field?effect. With the ion gel, the transconductance increases by ?10 000×, enabling the recording of biological action potentials.Conjugated?polymer?based organic electrochemical transistors (OECTs) are being studied for applications ranging from biochemical sensing to neural interfaces. While new polymers that interface digital electronics with the aqueous chemistry of life are being developed, the majority of high?performance organic transistor materials are poor at transporting biologically relevant ions. Here, the operating mode of an organic transistor is changed from that of an electrolyte?gated organic field?effect transistor (EGOFET) to that of an OECT by incorporating an ion exchange gel between the active layer and the aqueous electrolyte. This device works by taking up biologically relevant ions from solution and injecting more hydrophobic ions into the active layer. Using poly[2,5?bis(3?tetradecylthiophen?2?yl) thieno[3,2?b]thiophene] as the active layer and a blend of an ionic liquid, 1?butyl?3?methylimidazolium bis(trifluoromethylsulfonyl)imide, and poly(vinylidene fluoride?co?hexafluoropropylene) as the ion exchange gel, four orders of magnitude improvement in device transconductance and a 100?fold increase in kinetics are demonstrated. The ability of the ion?exchange?gel OECT to record biological signals by measuring the action potentials of a Venus flytrap is demonstrated. These results show the possibility of using interface engineering to open up a wider palette of organic semiconductors as OECTs that can be gated by aqueous solutions.