The electronics surrounding us in our daily lives rely almost exclusively on electrons as the dominant charge carrier. In stark contrast, biological systems rarely use electrons but rather use ions and molecules of varying size. Due to the unique combination of both electronic and ionic/molecular conductivity in conducting and semiconducting organic polymers and small molecules, these materials have emerged in recent decades as excellent tools for translating signals between these two realms and, therefore, providing a means to effectively interface biology with conventional electronics-thus, the field of organic bioelectronics. Today, organic bioelectronics defines a generic platform with unprecedented biological recording and regulation tools and is maturing toward applications ranging from life sciences to the clinic. In this Review, we introduce the field, from its early breakthroughs to its current results and future challenges.

Many biomolecules are charged and may therefore be transported with ionic currents. As a step toward addressable ionic delivery circuits, we report on the development of a npn ion bipolar junction transistor (npn-IBJT) as an active control element of anionic currents in general, and specifically, demonstrate actively modulated delivery of the neurotransmitter glutamic acid. The functional materials of this transistor are ion exchange layers and conjugated polymers. The npn-IBJT shows stable transistor characteristics over extensive time of operation and ion current switch times below 10 s. Our results promise complementary chemical circuits similar to the electronic equivalence, which has proven invaluable in conventional electronic applications.

comprises materials and devices that can fulfill just this dual ionic-electronic capability. Iontronics utilize the coupling of electrical and ionic signals in conducing polymers, leading to, for example, organic electrochemical transistors (OECTs), [2] electrolyte-gated (also known as electric doublelayer capacitor-gated) organic field-effect transistors (EGOFETs), [3,4] organic electrochemical biosensors, [5,6] and iontronic delivery electrodes and devices. [7][8][9][10][11] In iontronic delivery devices (Figure 1), chemical gradients are created by controlled release of charged biomolecules (ions) at specific locations at specific times. [7,8,12] Ions are transported to these release sites through ionic conductors due to applied electric fields between electrodes. The ionic conductors form the foundation of iontronic resistors (organic electronic ion pumps, OEIPs), diodes, and transistors which can be combined into circuits for, for example, multiplexing, addressing, and signal processing. These iontronic circuits behave analogous to traditional electronics, but use ions as charge carriers rather than electrons, and allow for the development of fully chemical systems generating complex signal patterns at high spatiotemporal resolution and biochemical specificity.There are several other techniques for electronic control of substance release, drug delivery, or ion transport related to this form of iontronics. These include techniques such as microfluidic and microelectromechanical systems (MEMS) based micropumps, [13] iontophoresis, [14,15] and organic electronic redox-mediated controlled release. [11,16] In comparison to these technologies, iontronic drug delivery provides a means of simultaneously achieving high delivery precision, minimal (or zero) liquid transport that could interfere with fragile biochemical microenvironments, continuous resupply of the transported substance, and (in principle) exact control over delivered amounts, even at speeds on par with synaptic signaling. In addition, as they are based on well-established solid-state device manufacturing techniques, iontronic components and systems can be miniaturized, addressed, and integrated with complex electronic systems in a straightforward manner. These features of iontronics combine to enable the lowest dose possible. With other techniques for substance release and transport, larger doses are often distributed (usually in solution phase) with less control, which could result in unwanted side effects. Other technologies have their advantages primarily in potentially simpler device design, the ability to transport larger molecules (e.g., In contrast to electronic systems, biology rarely uses electrons as the signal to regulate functions, but rather ions and molecules of varying size. Due to the unique combination of both electronic and ionic/molecular conductivity in conjugated polymers and polyelectrolytes, these materials have emerged as an excellent tool for translating signals between these two realms, hence the field of organic bioelectroni...

Electronic control over the generation, transport, and delivery of ions is useful in order to regulate reactions, functions, and processes in 5 various chemical and biological systems. Different kinds of ion diodes and transistors that exhibit non-linear current versus voltage characteristics have been explored to generate chemical gradients and signals. Bipolar membranes (BMs) exhibit both ion current rectification and water splitting and are thus suitable as ion diodes for the regulation of pH. To date, fast switching ion diodes have been difficult to realize due to accumulation of ions inside the device structure at forward bias -charges that take a long time to deplete at reverse bias. Water splitting occurs at elevated reverse voltage bias and is a feature that renders high ion current rectification impossible. 10This makes integration of ion diodes in circuits difficult. Here, we report three different designs of micro-fabricated ion bipolar membrane diodes (IBMDs). The first two designs consist of single BM configurations, and are capable of either splitting water or providing high current rectification. In the third design, water-splitting BMs and a highly-rectifying BM are connected in series, thus suppressing accumulation of ions. The resulting IBMD shows less hysteresis, faster off-switching, and also a high ion current rectification ratio as compared to the single BM devices. Further, the IBMD was integrated in a diode-based AND gate, which is capable 15 of controlling delivery of a hydroxide ions into a receiving reservoir.

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