Device design principles and bioelectronic applications for flexible organic electrochemical transistors

Organic electrochemical transistors(OECTs) exhibit significant potential for applications in healthcare and human-machine interfaces, due to their tunable synthesis, facile deposition, and excellent biocompatibility. Expanding OECTs to the fexible devices will significantly facilitate stable contact with the skin and enable more possible bioelectronic applications. In this work,we summarize the device physics of fexible OECTs, aiming to offer a foundational understanding and guidelines for material selection and device architecture. Particular attention is paid to the advanced manufacturing approaches, including photolithography and printing techniques, which establish a robust foundation for the commercialization and large-scale fabrication. And abundantly demonstrated examples ranging from biosensors, artificial synapses/neurons, to bioinspired nervous systems are summarized to highlight the considerable prospects of smart healthcare. In the end, the challenges and opportunities are proposed for fexible OECTs. The purpose of this review is not only to elaborate on the basic design principles of fexible OECTs, but also to act as a roadmap for further exploration of wearable OECTs in advanced bio-applications.

Layer by Layer Self-assembly Fiber-based Flexible Electrochemical Transistor

Poly(3,4-ethylenedioxyethiophene)-polystyrene sulfonic acid(PEDOT:PSS)/polyallyl dimethyl ammonium chloride modified reduced graphene oxide(PDDA-rGO)was layer by layer self-assembled on the cotton fiber.The surface morphology and electric property was investigated.The results confirmed the dense membrane of PEDOT:PSS and the lamellar structure of PDDA-rGO on the fibers.It has excellent electrical conductivity and mechanical properties.The fiber based electrochemical transistor(FECTs)prepared by the composite conductive fiber has a maximum output current of 8.7 mA,a transconductance peak of 10 mS,an on time of 1.37 s,an off time of 1.6 s and excellent switching stability.Most importantly,the devices by layer by layer self-assembly technology opens a path for the true integration of organic electronics with traditional textile technologies and materials,laying the foundation for their later widespread application.

Organic Electrochemical Transistor based on Polypyrrole/ Crosslinked Chitosan/Nylon Fibers

Glutaraldehyde(GA)crosslinked chitosan(CHIT)was modified on nylon fibers.Afterwards,pyrrole was in-situ polymerized on the surface of the CHIT/Nylon fiber.The SEM and FT-IR results show that the functional fiber is successfully prepared,and the obtained polypyrrole(PPy)presents nanorods morphology on the fiber surface.The mechanical properties of the fibers were studied by Instron.The organic electrochemical transistors based on PPy/Nylon fiber,PPy/CHIT/Nylon fiber,and PPy/GA-CHIT/Nylon fiber as channels were prepared and their transistors performance was compared.It is found that PPy/GA-CHIT/Nylon fiber-based transistor has great output,transfer,transient curves,and excellent transconductance of 6.8 mS,providing a new platform for the field of wearable devices.Furthermore,the study introduces chitosan material with excellent biocompatibility,which makes prepared transistors also have potential applications in the field of biosensing.

Artificial synapses based on organic electrochemical transistors with self-healing dielectric layers

Organic electrochemical transistors(OECTs)have emerged as one type of promising building block for neuromorphic systems owing to their capability of mimicking the morphology and functions of biological neurons and synapses.Currently,numerous kinds of OECTs have been developed,while self-healing performance has been neglected in most reported OECTs.In this work,the OECTs using self-healing polymer electrolytes as dielectric layers are proposed.Several important synaptic behaviors are simulated in the OECTs by doping the channel layers with ions from the electrolytes.Benefitting from the dynamic hydrogen bonds in the self-healing polymer electrolytes,the OECTs can successfully maintain their electrical performance and the ability of emulating synaptic behaviors after self-healing compared with the initial state.More significantly,the sublinear spatial summation function is demonstrated in the OECTs and their potential in flexible electronics is also validated.These results suggest that our devices are expected to be a vital component in the development of future wearable and bioimplantable neuromorphic systems.

High-Transconductance,Highly Elastic,Durable and Recyclable All-Polymer Electrochemical Transistors with 3D Micro-Engineered Interfaces

Organic electrochemical transistors(OECTs)have emerged as versatile platforms for broad applications spanning from flexible and wearable integrated circuits to biomedical monitoring to neuromorphic computing.A variety of materials and tailored micro/nanostructures have recently been developed to realized stretchable OECTs,however,a solid-state OECT with high elasticity has not been demonstrated to date.Herein,we present a general platform developed for the facile generation of highly elastic all-polymer OECTs with high transconductance(up to 12.7 mS),long-term mechanical and environmental durability,and sustainability.Rapid prototyping of these devices was achieved simply by transfer printing lithium bis(trifluoromethane)sulfonimide doped poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)(PEDOT:PSS/LiTFSI)microstructures onto a resilient gelatin-based gel electrolyte,in which both depletion-mode and enhancement-mode OECTs were produced using various active channels.Remarkably,the elaborate 3D architectures of the PEDOT:PSS were engineered,and an imprinted 3D-microstructured channel/electrolyte interface combined with wrinkled electrodes provided performance that was retained(>70%)through biaxial stretching of 100%strain and after 1000 repeated cycles of 80%strain.Furthermore,the anti-drying and degradable gelatin and the self-crosslinked PEDOT:PSS/LiTFSI jointly enabled stability during>4 months of storage and on-demand disposal and recycling.This work thus represents a straightforward approach towards high-performance stretchable organic electronics for wearable/implantable/neuromorphic/sustainable applications.

基于浮栅OECT传感的归一化灵敏度优化

浮栅有机电化学晶体管(OECT)作为一种新兴的传感检测平台,由于其工作电压低、制备简单、传感与检测可分离的优点,被广泛应用于生化传感检测。研究了对浮栅OECT归一化灵敏度的影响因素。通过对pH、Na^(+)、H_(2)O_(2)进行恒电位测试,系统探究了浮栅OECT的跨导(gm)及次级浮动栅极FG2面积(A_(FG2))对归一化灵敏度的影响。实验结果表明,在一定电压范围内,器件检测灵敏度随器件跨导的增大而增大。此外,A_(FG2)增加时,根据串联电容分压的方式,电容型传感(pH、Na^(+)检测)及电荷转移型传感(H_(2)O_(2)检测)的有机半导体/电解质处有效栅压、跨导均增加,进而导致归一化灵敏度大幅提高。总体而言,增大gm和A_(FG2)均可有效提高检测灵敏度。同时,实现了对pH、Na^(+)、H_(2)O_(2)的高灵敏度检测,pH检测灵敏度最高为0.069/pH,Na^(+)检测灵敏度最高为0.027 dec-1,H_(2)O_(2)检测灵敏度最高为0.33 dec-1,检测灵敏度均高于同类传感器。

Stretchable organic electrochemical transistors via threedimensional porous elastic semiconducting films for artificial synaptic applications

Neuromorphic computing targets realizing biomimetic or intelligence systems capable of processing abundant tasks in parallel analogously to our brain,and organic electrochemical transistors(OECTs)that rely on the mixed ionic-electronic synergistic couple possess significant similarity to biological systems for implementing synaptic functions.However,the lack of reliable stretchability for synaptic OECTs,where mechanical deformation occurs,leads to consequent degradation of electrical performance.Herein,we demonstrate stretchable synaptic OECTs by adopting a three-dimensional poly(3-hexylthiophene)(P3HT)/styrene-ethylene-butylene-styrene(SEBS)blend porous elastic film for neuromorphic computing.Such architecture shows the full capability to emulate biological synaptic behaviors.Adjusting the accumulated layer numbers of porous film enables tunable OECT output and hysteresis,resulting in transition in plasticity.Especially,with a trilayer porous film,large-scale conductance and hysteresis are endorsed for efficient mimicking of memory-dependent synapse behavior.Benefitted from the interconnected three-dimensional porous structures,corresponding stretchable synaptic OECTs exhibit excellent mechanical robustness when stretched at a 30%strain,and maintain reliable electrical characteristics after 500 stretching cycles.Furthermore,near-ideal weight updates with near-zero nonlinearities,symmetricity in long-term potentiation(LTP)and depression,and applications for image simulation are validated.This work paves a universal design strategy toward highperformance stretchable neuromorphic computing architecture and could be extended to other flexible/stretchable electronics.

High-gain signal-on PEDOT:PSS organic photoelectrochemical transistor biosensing modulated by a MXene/MOFs/NiO Schottky heterojunction

Herein we report a high-gain signal-on poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)(PEDOT:PSS)organic electrochemical transistor(OECT)biosensing using an accumulation-mode PEDOT:PSS OECT modulated by a light-fueled MXene/MOFs/Ni O Schottky heterojunction.In such a system,the MXene/MOFs/Ni O Schottky heterojunction exhibited superior gating effect,as it not only enabled the fast-directional charge transfer but also guaranteed the maximal accessibility of the electrolyte to topped 2D MXene with large surface area.In linkage with a bi-enzyme cascade system,the quinone derivatives produced by the cascade reaction of alkaline phosphatase(ALP)and tyrosinase(TYR)could serve as effective electron acceptors for the representative Ti_(3)C_(2)/PCN-224/Ni O heterojunction,underpinning an innovative method for sensitive detection of ALP activity with a low detection limit of 0.001 U L^(-1).Remarkably,the as-developed system demonstrated a remarkable current gain as high as near 10^(4),which to our knowledge is the highest one among existing OECT biosensory devices.This work represents a generic protocol to develop the novel signal-on PEDOT:PSS OECT platform towards biochemical detection and beyond.

Coaxial fiber organic electrochemical transistor with high transconductance

Fiber organic electrochemical transistors(OECTs)have received extensive attention in wearable and implantable biosensors because of their high flexibility and low working voltage.However,the transconductance of fiber OECTs is much lower compared with the planar counterparts,leading to low sensitivity.Here,we developed fiber OECTs in a coaxial configuration with microscale channel length to achieve the highest transconductance of 135 mS,which is one to two orders of magnitude higher than that of the state-of-the-art fiber OECTs.Coaxial fiber OECT based sensors showed high sensitivities of 12.78,20.53 and 3.78 mA/decade to ascorbic acid,hydrogen peroxide and glucose,respectively.These fiber OECTs were woven into a fabric to monitor the glucose in sweat during exercise and implanted in mouse brain to detect ascorbic acid.This coaxial architectural design offers an effective way to promote the performance of fiber OECTs and realize highly sensitive detection of biochemicals.

Plasmonic organic electrochemical transistors for enhanced sensing

Organic electrochemical transistors(OECTs)have been hailed as highly sensitive biomolecular sensors among organic electronic devices due to their superior stability in an aqueous environment and high transconductance.At the same time,plasmon based sensors are known to provide high sensitivity for biosensing due to the highly localized plasmonic field.Here we report a plasmonic OECT(POET)device that synchronizes the advantages of OECTs and plasmonic sensors on a single platform.The platform is fabricated by a simple,cost-effective,and high-throughput nanoimprinting process,which allows plasmonic resonance peak tuning to a given visible wavelength of interest for versatile biosensing.With glucose sensing as proof,a five-times sensitivity enhancement is obtained for POET compared to a regular(non-plasmonic)OECT.Thus,the POET paves the way to a new paradigm of optoelectronic sensors that combines the inherent high sensitivity of OECTs and localized plasmonic field to sense a vast realm of biomolecules.

High-performance organic electrochemical transistors gated with 3D-printed graphene oxide electrodes

Organic electrochemical transistors(OECTs)have garnered significant interest due to their ability to facilitate both ionic and electronic transport.A large proportion of research efforts thus far have focused on investigating high-performance materials that can serve as mixed ion doping and charge transport layers.However,relatively less attention has been given to the gateelectrode materials,which play a critical role in controlling operational voltage,redox processes,and stability,especially in the context of semiconductor-based OECTs working in accumulation mode.Moreover,the demand for planarity and flexibility in modern bioelectronic devices presents significant challenges for the commonly used Ag/AgCl electrodes in OECTs.Herein,we report the construction of high-performance accumulation-mode OECTs by utilizing a gate electrode made of three-dimensional(3D)-printed graphene oxide.The 3D-printed graphene oxide electrode incorporating one-dimensional(1D)carbon nanotubes,is directly printed using an aqueous-based ink and showcases exceptional mechanical flexibility and porosity properties,enabling high-throughput preparation for both top gates and integrated planar architecture,as well as fast ion/charge transport.OECTs with high performance comparable to that of Ag/AgCl-gated OECTs are thus achieved and present promising feasibility for electrocardiograph(ECG)signal recording.This provides a promising choice for the application of flexible bioelectronics in medical care and neurological recording.

Metal–Organic Framework-Based Sensors for Environmental Contaminant Sensing

Increasing demand for timely and accurate environmental pollution monitoring and control requires new sensing techniques with outstanding performance, i.e.,high sensitivity, high selectivity, and reliability. Metal–organic frameworks(MOFs), also known as porous coordination polymers, are a fascinating class of highly ordered crystalline coordination polymers formed by the coordination of metal ions/clusters and organic bridging linkers/ligands. Owing to their unique structures and properties,i.e., high surface area, tailorable pore size, high density of active sites, and high catalytic activity, various MOF-based sensing platforms have been reported for environmental contaminant detection including anions, heavy metal ions,organic compounds, and gases. In this review, recent progress in MOF-based environmental sensors is introduced with a focus on optical, electrochemical, and field-effect transistor sensors. The sensors have shown unique and promising performance in water and gas contaminant sensing. Moreover, by incorporation with other functional materials, MOF-based composites can greatly improve the sensor performance. The current limitations and future directions of MOF-based sensors are also discussed.

PEDOT:PSS/PAN纳米纤维复合纱线晶体管制备及性能

为得到高调制性能的柔性有机电化学晶体管(OECTs),采用共轭静电纺纱技术制备以涤纶线为芯纱聚丙烯腈(PAN)为壳层的芯-壳结构复合纳米纤维纱线,PAN浓度为12%时,复合纳米纤维纱线拉伸强度为18.6 MPa,比面积为1.078 m2/g。通过在纱线上负载聚(3,4-乙烯二氧噻吩)∶聚(苯乙烯磺酸盐)(PEDOT∶PSS)作为OECTs的沟道材料,并构建为平行结构纱线OECTs。晶体管的调制性能测试表明该纱线晶体管可以通过控制栅极电压实现电解质对PEDOT∶PSS沟道不同程度的掺杂/去掺杂效应,进而调制沟道电流大小。

基于可拉伸有机晶体管的高性能生理信号传感器

近来,以共轭聚合物为沟道材料的有机电化学晶体管(OECT)因其易于制备、具有离子–电子转换能力和生物界面相容性而成为研究热点。然而,已报道的用于OECT沟道材料的大多是p型共轭聚合物,而基于n型共轭聚合物开发的OECT则很少,而不平衡的发展阻碍了复杂互补电路的实现。最近被报道的新兴n型共轭聚合物半导体Poly (benzimidazobenzophenanthroline)(BBL) OECT为解决上述问题提供了一个有效的方案。但BBL薄膜本身具有脆性无法拉伸,无法满足柔性器件的使用需求,大大阻碍了其应用及发展。本工作中,我们提出了一种器件可拉伸的n型BBL OECT器件的制备方法,并验证了其在汗液传感方面的可行性。

氯仿改性聚(3-己基噻吩)有机电化学晶体管及其神经突触功能模仿

通过旋涂法制备了有机半导体聚(3-己基噻吩)(P3HT)薄膜,在二氯苯溶剂中引入氯仿对P3HT薄膜进行改性。以改性的P3HT薄膜作为沟道层,以离子凝胶作为电解质层制备了有机电化学晶体管(OECT)。通过原子力显微镜、紫外-可见光谱和拉曼光谱探究了氯仿改性对P3HT薄膜粗糙度和分子有序度的影响,采用半导体参数仪研究了氯仿改性对材料电学性能的影响。实验结果表明,氯仿改性降低了P3HT薄膜的粗糙度,提高了分子排列的有序度。氯仿改性后的OECT在−0.5 V和−1.0 V的电脉冲刺激下呈现显著的神经突触兴奋脉冲电流响应特性,相比于未改性的器件,电导调控幅值分别增加了约2倍和16倍,且延长了其保持特性。基于氯仿改性OECT的人工神经突触网络将MNIST手写数字识别准确率从73.6%提高至92.7%,有望在高性能神经形态计算方面发挥重要作用。

共价有机框架作为通道材料的有机电化学晶体管的制备及性能

有机电化学晶体管(OECT)由于具有器件制造简单、可拉伸、相对较低的工作电压和良好的开关电流比等优点,被广泛应用于生物医学、环境监测、保健产品、水处理和食品检测等领域。然而有机电化学晶体管材料往往受限于沟道材料的低化学稳定性以及低电子和离子迁移率等。共价有机框架(COF)由于具有稳定的共价键、良好的面内π-π共轭以及面外有序结构有望成为新一代的OECT沟道材料。文章通过一种表面引发方法在硅片表面原位生长COF薄膜,并用于OECT器件的组装,具有约100倍的开关比、0.4 V的低阈值电压和0.53 cm^(2)(V·s)的场效应迁移率。该研究结果为共价有机框架薄膜应用于电子器件领域拓宽了道路。

Fiber-shaped organic electrochemical transistors for biochemical detections with high sensitivity and stability

Precise and continuous monitoring of biochemicals by biosensors assists to understand physiological functions for various diagnostics and therapeutic applications.For implanted biosensors,small size and flexibility are essential for minimizing tissue damage and achieving accurate detection.However,the active surface area of sensor decreases as the sensor becomes smaller,which will increase the impedance and decrease the signal to noise ratio,resulting in a poor detection limit.Taking advantages of local amplification effect,organic electrochemical transistors(OECTs)constitute promising candidates for high-sensitive monitoring.However,their detections in deep tissues are rarely reported.Herein,we report a family of implantable,fiber-shaped all-in-one OECTs based on carbon nanotube fibers for versatile biochemical detection including H2O2,glucose,dopamine and glutamate.These fiber-shaped OECTs demonstrated high sensitivity,dynamical stability in physiological environment and antiinterference capability.After implantation in mouse brain,7-day dopamine monitoring in vivo was realized for the first time.These fiber-shaped OECTs could be great additions to the"life science"tool box and represent promising avenue for biomedical monitoring.

Molecule-based vertical transistor via intermolecular charge transport throughπ-πstacking

Theπ-πstacking is a well-recognized intermolecular interaction that is responsible for the construction of electron hopping channels in numerous conducting frameworks/aggregates.However,the exact role ofπ-to-πchannels within typical single crystalline organic semiconductors remains unclear as the orientations of these molecules are diverse,and their control usually requires additional side chain groups that misrepresent the intrinsic properties of the original semiconducting molecules.Therefore,the construction of conduction channels with intrinsicπ-πstacking in the molecule-based device is crucial for the utilization of their unique transport characteristics and understanding of the transport mechanism.To this end,we present a molecular intercalation strategy that integrates two-dimensional layered materials with functional organic semiconductor molecules for functional molecule-based electronics.Various organic semiconductor molecules can be effectively intercalated into the van der Waals gaps of semi-metallic TaS_(2) withπ-πstacking configuration and controlled intercalant content.Our results show that the vertical charge transport in the stacking direction shows a tunneling-dominated mechanism that strongly depends on the molecular structures.Furthermore,we demonstrated a new type of molecule-based vertical transistor in which TaS_(2) andπ-πstacked organic molecules function as the electrical contact and the active channel,respectively.On/off ratios as high as 447 are achieved under electrostatic modulation in ionic liquid,comparable to the current state-of-the-art molecular transistors.Our study provides an ideal platform for probing intrinsic charge transport acrossπ-πstacked conjugated molecules and also a feasible approach for the construction of high-performance molecule-based electronic devices.

Real-time detection of Cu(Ⅱ)with PEDOT:PSS based organic electrochemical transistors

Copper is an essential element in the environment and the human body,but at the same time,exposure to high concentrations of Cu^(2+) ions will potentially lead to acute toxicity and various neurodegenerative diseases.Thus,it is of great significance for the development of highly sensitive and selective strategies for the detection of Cu^(2+) ions.Here,we report a highly efficient poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid)(PEDOT:PSS) based organic electrochemical transistor(OECT)sensor,for real-time Cu^(2+) ions detection.The detection limit of the OECT device is as low as 100 nM,far beyond the sensitivity required for practical uses.The detection mechanism may base on the chemical reactivity of Cu^(2+) ions oxiding the PEDOT:PSS in solution both in absence and presence of the base potential.The OECT devices also exhibit excellent selective response to Cu^(2+)ions rather than other metal ions.Finally,we also demonstrate the determination of Cu^(2+) ions in tap water with the OECT Cu^(2+)sensor.Considering the high sensitivity and selectivity,as well as the real-time and low cost features of our Cu^(2+) OECT sensor,it is ideal for portable and disposable applications for environment monitoring and public health.

Flexible organic electrochemical transistors for chemical and biological sensing

Chemical and biological sensing play important roles in healthcare,environmental science,food-safety tests,and medical applications.Flexible organic electrochemical transistors(OECTs)have shown great promise in the field of chemical and biological sensing,owing to their superior sensitivity,high biocompatibility,low cost,and light weight.Herein,we summarize recent progress in the fabrication of flexible OECTs and their applications in chemical and biological sensing.We start with a brief introduction to the working principle,configuration,and sensing mechanism of the flexible OECT-based sensors.Then,we focus on the fabrication of flexible OECT-based sensors,including material selection and structural engineering of the components in OECTs:the substrate,electrodes,electrolyte,and channel.Particularly,the gate modification is discussed extensively.Then,the applications of OECT-based sensors in chemical and biological sensing are reviewed in detail.Especially,the array-based and integrated OECT sensors are also introduced.Finally,we present the conclusions and remaining challenges in the field of flexible OECT-based sensing.Our timely review will deepen the understanding of the flexible OECT-based sensors and promote the further development of the fast-growing field of flexible sensing.