Ion exchange gels enhance organic electrochemical transistor performance in aqueous solution

TL;DR

This study introduces an ion exchange gel into organic electrochemical transistors, significantly improving their ability to interface with biological ions and signals, thereby expanding their potential applications in bioelectronics.

Contribution

The paper demonstrates that incorporating an ion exchange gel into OECTs enhances ion uptake and injection, enabling the use of a broader range of organic semiconductors for biological interfacing.

Findings

Over four orders of magnitude increase in transconductance

Hundred-fold faster ion injection kinetics

Successful recording of plant action potentials

Abstract

Conjugated polymer-based organic electrochemical transistors (OECTs) are being studied for applications ranging from biochemical sensing to neural interfaces. While new conjugated polymers are being developed that can interface digital electronics with the aqueous chemistry of life, the vast majority of high-performance, high-mobility organic transistor materials developed over the past decades are extremely poor at taking up biologically-relevant ions. Here we incorporate an ion exchange gel into an OECT, demonstrating that this structure is capable of taking up biologically-relevant ions from solution and injecting larger, more hydrophobic ions into the underlying polymer semiconductor active layer in multiple hydrophobic conjugated polymers. Using poly[2,5-bis(3-tetradecylthiophen-2-yl) thieno[3,2-b]thiophene] (PBTTT) as a model semiconductor active layer and a blend of the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM TFSI) and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) as the ion exchange gel, we demonstrate more than a four order of magnitude improvement in OECT device transconductance and a one hundred-fold increase in ion injection kinetics. We demonstrate the ability of the ion exchange gel OECT to record biological signals by measuring the action potentials of a Venus flytrap plant. These results show the possibility of using interface engineering to open up a wider palette of organic semiconductor materials as OECTs that can be gated by aqueous solutions.