No abstract

The organic electrochemical transistor (OECT) with a conjugated polymer as the active material is the elementary unit of organic bioelectronic devices. Improved functionalities, such as low power consumption, can be achieved by building complementary circuits featuring two or more OECTs. Complementary circuits commonly combine both p‐ and n‐type transistors to reduce power draw. While p‐type OECTs are readily available, n‐type OECTs are less common mainly due to poor stability of the n‐type active channel material in aqueous electrolyte. Here, a complementary circuit is made using a pair of OECTs having polyaniline (PANI) as the channel material in both transistors. PANI, with a finite electrochemical window accessible at voltages lower than 1 V, exhibits a peak in current versus gate voltage when used as an active channel in an OECT. The current peak has two slopes, one n‐like and one p‐like, which correspond to different electrochemical regimes of the same underlying conjugated polymer. The electrochemistry enables the design of a complementary circuit using only PANI as the channel material. The PANI‐based circuit is shown to have excellent performance with gain of ≈7 and is transferred on a flexible biocompatible chitosan substrate with demonstrated operation in aqueous electrolyte.

Modulating the cell membrane potential provides an opportunity to control electrical signaling that is central to cellular physiology and its proper biological function. Among the many technological tools available to enable this modulation, optical stimulation through a photoactive substrate is a powerful strategy that is minimally invasive and wireless. This is critical to avoid disrupting the structural integrity of the cell membrane that is often caused by the use of electrical stimulation electrodes or changing its genetic footprints if optogenetics is the approach taken to photomodulate its electrophysiology. The use of a photoactive substrate such as an organic semiconductor combines optoelectronic properties with mechanical tissue compatibility, which is unachievable with inorganic semiconductors. This research news first discusses the mechanisms of cell photostimulation via these organic photoactive substrates and techniques employed to characterize their photoresponse. Then a summary of the relevant organic materials and their recent applications in cellular photostimulation is presented. Finally, the challenges in the field are described and a perspective on how to address these is provided.