Poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate),
PSS, has been utilized for over two decades as a stable, solution-processable hole conductor. While its hole transport properties ...have been the subject of intense investigation, recent work has turned to
PSS as a mixed ionic/electronic conductor in applications including bioelectronics, energy storage and management, and soft robotics. Conducting polymers can efficiently transport both holes and ions when sufficiently hydrated, however, little is known about the role of morphology on mixed conduction. Here, we show that bulk ionic and electronic mobilities are simultaneously affected by processing-induced changes in nano- and meso-scale structure in
PSS films. We quantify domain composition, and find that domain purification on addition of dispersion co-solvents limits ion mobility, even while electronic conductivity improves. We show that an optimal morphology allows for the balanced ionic and electronic transport that is critical for prototypical mixed conductor devices. These findings may pave the way for the rational design of polymeric materials and processing routes to enhance devices reliant on mixed conduction.
Organic electrochemical transistors (OECTs) hold promise for developing a variety of high‐performance (bio‐)electronic devices/circuits. While OECTs based on p‐type semiconductors have achieved ...tremendous progress in recent years, n‐type OECTs still suffer from low performance, hampering the development of power‐efficient electronics. Here, it is demonstrated that fine‐tuning the molecular weight of the rigid, ladder‐type n‐type polymer poly(benzimidazobenzophenanthroline) (BBL) by only one order of magnitude (from 4.9 to 51 kDa) enables the development of n‐type OECTs with record‐high geometry‐normalized transconductance (gm,norm ≈ 11 S cm−1) and electron mobility × volumetric capacitance (µC* ≈ 26 F cm−1 V−1 s−1), fast temporal response (0.38 ms), and low threshold voltage (0.15 V). This enhancement in OECT performance is ascribed to a more efficient intermolecular charge transport in high‐molecular‐weight BBL than in the low‐molecular‐weight counterpart. OECT‐based complementary inverters are also demonstrated with record‐high voltage gains of up to 100 V V−1 and ultralow power consumption down to 0.32 nW, depending on the supply voltage. These devices are among the best sub‐1 V complementary inverters reported to date. These findings demonstrate the importance of molecular weight in optimizing the OECT performance of rigid organic mixed ionic–electronic conductors and open for a new generation of power‐efficient organic (bio‐)electronic devices.
n‐Type organic electrochemical transistors (OECTs) underperform compared to p‐type OECTs. By tuning the molecular weight of the rigid ladder‐type poly(benzimidazobenzophenanthroline), n‐type OECTs with record‐high figures of merit are reported. OECT‐based complementary inverters are also demonstrated with high voltage gains of up to 100 V V−1 and ultralow power consumption down to 0.32 nW, depending on the supply voltage.
Organic electrochemical transistors (OECTs) are promising transducers for biointerfacing due to their high transconductance, biocompatibility, and availability in a variety of form factors. Most ...OECTs reported to date, however, utilize rather large channels, limiting the transistor performance and resulting in a low transistor density. This is typically a consequence of limitations associated with traditional fabrication methods and with 2D substrates. Here, the fabrication and characterization of OECTs with vertically stacked contacts, which overcome these limitations, is reported. The resulting vertical transistors exhibit a reduced footprint, increased intrinsic transconductance of up to 57 mS, and a geometry‐normalized transconductance of 814 S m−1. The fabrication process is straightforward and compatible with sensitive organic materials, and allows exceptional control over the transistor channel length. This novel 3D fabrication method is particularly suited for applications where high density is needed, such as in implantable devices.
Vertical organic electrochemical transistors are demonstrated with decreased channel length down to 450 nm, while retaining a simple fabrication process. These devices exhibit an intrinsic transconductance of up to 57 mS and a geometry‐normalized transconductance of 814 S m−1. The reduced spatial footprint and improved device performance are particularly suited for biointerfacing applications.
Despite recent interest in organic electrochemical transistors (OECTs), sparked by their straightforward fabrication and high performance, the fundamental mechanism behind their operation remains ...largely unexplored. OECTs use an electrolyte in direct contact with a polymer channel as part of their device structure. Hence, they offer facile integration with biological milieux and are currently used as amplifying transducers for bioelectronics. Ion exchange between electrolyte and channel is believed to take place in OECTs, although the extent of this process and its impact on device characteristics are still unknown. We show that the uptake of ions from an electrolyte into a film of poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonate (
PSS) leads to a purely volumetric capacitance of 39 F/cm(3). This results in a dependence of the transconductance on channel thickness, a new degree of freedom that we exploit to demonstrate high-quality recordings of human brain rhythms. Our results bring to the forefront a transistor class in which performance can be tuned independently of device footprint and provide guidelines for the design of materials that will lead to state-of-the-art transistor performance.
Abstract Without intervention, cardiac arrhythmias pose a risk of fatality. However, timely intervention can be challenging in environments where transporting a large, heavy defibrillator is ...impractical, or emergency surgery to implant cardiac stimulation devices is not feasible. Here, we introduce an injectable cardiac stimulator, a syringe loaded with a nanoparticle solution comprising a conductive polymer and a monomer that, upon injection, forms a conductive structure around the heart for cardiac stimulation. Following treatment, the electrode is cleared from the body, eliminating the need for surgical extraction. The mixture adheres to the beating heart in vivo without disrupting its normal rhythm. The electrofunctionalized injectable cardiac stimulator demonstrates a tissue-compatible Young’s modulus of 21 kPa and a high conductivity of 55 S/cm. The injected electrode facilitates electrocardiogram measurements, regulates heartbeat in vivo, and rectifies arrhythmia. Conductive functionality is maintained for five consecutive days, and no toxicity is observed at the organism, organ, or cellular levels.
Extracellular electron transfer (EET) denotes the process of microbial respiration with electron transfer to extracellular acceptors and has been exploited in a range of microbial electrochemical ...systems (MESs). To further understand EET and to optimize the performance of MESs, a better understanding of the dynamics at the microscale is needed. However, the real‐time monitoring of EET at high spatiotemporal resolution would require sophisticated signal amplification. To amplify local EET signals, a miniaturized bioelectronic device, the so‐called organic microbial electrochemical transistor (OMECT), is developed, which includes Shewanella oneidensis MR‐1 integrated onto organic electrochemical transistors comprising poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) combined with poly(vinyl alcohol) (PVA). Bacteria are attached to the gate of the transistor by a chronoamperometric method and the successful attachment is confirmed by fluorescence microscopy. Monitoring EET with the OMECT configuration is achieved due to the inherent amplification of the transistor, revealing fast time‐responses to lactate. The limits of detection when using microfabricated gates as charge collectors are also investigated. The work is a first step toward understanding and monitoring EET in highly confined spaces via microfabricated organic electronic devices, and it can be of importance to study exoelectrogens in microenvironments, such as those of the human microbiome.
The real‐time monitoring of extracellular electron transfer at the microscale is demonstrated with rapid response to lactate, without sophisticated signal amplification. The miniaturized bioelectronic device includes Shewanella oneidensis MR‐1 integrated onto organic electrochemical transistors comprising poly(3,4‐ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) and poly(vinyl alcohol) (PVA). The work can be important to study exoelectrogens in microenvironments, such as in the human microbiome.
From cell‐to‐cell communication to metabolic reactions, ions and protons (H+) play a central role in many biological processes. Examples of H+ in action include oxidative phosphorylation, acid ...sensitive ion channels, and pH dependent enzymatic reactions. To monitor and control biological reactions in biology and medicine, it is desirable to have electronic devices with ionic and protonic currents. Here, we summarize our latest efforts on bioprotonic devices that monitor and control a current of H+ in physiological conditions, and discuss future potential applications. Specifically, we describe the integration of these devices with enzymatic logic gates, bioluminescent reactions, and ion channels.
Bioprotonic devices can monitor, and control H+ currents for biological applications. Pd/PdHx couple is used as a transducer of H+ currents into electronic currents and vice versa. The use of Pd/PdHx in bioelectronics has opened the doors to new type of applications and devices including enzyme logic, control of bioluminescence, and platforms for integration of ion channels toward intracellular communication.
For the majority of biosensors or biomedical devices, immobilization of the biorecognition element is a critical step for device function. To achieve longer lifetime devices and controllable ...functionalization, covalent immobilisation techniques are preferred over passive adhesion and electrostatic interactions. The rapidly emerging field of organic bioelectronics uses conducting polymers (or small molecules) as the active materials for transduction of the biological signal to an electronic one. While a number of techniques have been utilized to entrap or functionalize conducting polymers deposited by electro- or vapor phase polymerization, covalent functionalization of solution processed films, essential for realizing low cost or high throughput fabrication, has not been thoroughly investigated. In this study we show a versatile biofunctionalization technique for the solution processable conducting polymer poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) PEDOT:PSS, which is a commercially available material, and has a record high conductivity. Addition of poly(vinyl alcohol) (PVA) into the solution with PEDOT:PSS provides a handle for subsequent silanization with a well-characterised silane reagent, allowing for covalent linkage of biological moieties onto PEDOT:PSS films. We show homogenous and large-scale biofunctionalization with polypeptides and proteins, as well as maintenance of the biological functionalities of the proteins. In addition, no deleterious effects are noted on the electronic or ionic transport properties of the conducting polymer films due to incorporation of the PVA.
The light-sensitive properties of organic electrochemical transistors (OECTs) based on polythiophene and PEDOT:PSS have been studied for the first time. It has been found that the maximum ...transconductance of a developed OECT shifts to higher gate voltages with the increase of light irradiation at the polythiophene gate electrode. This gate material chosen for the OECT plays an important role in the light-enhanced oxygen reduction reaction (ORR), which is subsequently responsible for the doping/de-doping of the channel material upon light illumination, thus making the OECT an efficient light sensing device. Additionally, the connection of these devices allowed the creation of organic opto-logic gates. This very first low voltage organic optical-to-electronic interface can potentially find applications in modern electronics and photonics. The development process includes geometry optimization and optimization of the channel and gate materials.
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