Bioelectronic Applications Research Articles

Enhanced Stability of N‐Type Organic Electrochemical Transistors Via Small‐Molecule Passivation

AbstractOrganic electrochemical transistors (OECTs) are of great interest owing to their potential applications in bioelectronics and neuromorphic systems. However, n‐type OECTs suffer from poor stability and facile degradation, mainly due to the oxygen reduction reactions in organic mixed ionic‐electronic conductors during device operation. In this study, a small‐molecule passivation strategy is introduced to greatly improve the stability of poly(benzobisimidazobenzophenanthroline) (BBL)‐based n‐type OECTs. 6,6‐Phenyl‐C61‐butyric acid methyl ester (PCBM) is spin‐coated onto the BBL layer to form a smooth and hydrophobic passivation layer, which effectively inhibits the oxygen reduction reactions while enabling ion permeation in aqueous electrolytes. Consequently, the OECTs employing the PCBM/BBL bilayers with an optimized PCBM thickness exhibit significantly improved operational stability at various electrolyte conditions (0.1 m NaCl or NaOH) and over a wide gate‐voltage sweep range (from −0.7 to 0.7 V). Owing to the high electron mobility of PCBM, the carrier mobility and switching speed of the PCBM/BBL OECTs are also improved compared with those of the pristine BBL OECTs. This study demonstrates the beneficial effects of simple surface passivation in organic mixed ionic‐electronic conductors and provides valuable insights for the design of high‐performance and stable OECTs for more specialized and advanced applications.

Replacing the Gallium Oxide Shell with Conductive Ag: Toward a Printable and Recyclable Composite for Highly Stretchable Electronics, Electromagnetic Shielding, and Thermal Interfaces.

Liquid metal (LM)-based composites hold promise for soft electronics due to their high conductivity and fluidic nature. However, the presence of α-Ga2O3 and GaOOH layers around LM droplets impairs conductivity and performance. We tackle this issue by replacing the oxide layer with conductive silver (Ag) using an ultrasonic-assisted galvanic replacement reaction. The Ag-coated nanoparticles form aggregated, porous microparticles that are mixed with styrene-isoprene-styrene (SIS) polymers, resulting in a digitally printable composite with superior electrical conductivity and electromechanical properties compared to conventional fillers. Adding more LM enhances these properties further. The composite achieves EMI shielding effectiveness (SE) exceeding 75 dB in the X-band frequency range, even at 200% strain, meeting stringent military and medical standards. It is applicable in wireless communications and Bluetooth signal blocking and as a thermal interface material (TIM). Additionally, we highlight its recyclability using a biodegradable solvent, underscoring its eco-friendly potential. This composite represents a significant advancement in stretchable electronics and EMI shielding, with implications for wearable and bioelectronic applications.

Continuous Phase Separation Induced Tough Hydrogel Fibers with Ultrahigh Conductivity for Multidimensional Soft Electronics

AbstractConductive hydrogel fibers exhibit great potential in soft robots, bioelectronics, and human–machine interfaces due to the unique combination of electrical conductivity, high water content, tissue‐like mechanical properties, and 1D structure. Despite significant advances in hydrogel technologies, the typical conductive hydrogel fibers show low conductivity (<10 S cm−1), weak mechanical properties, and water stability, which makes it challenging to satisfy the requirements of practical applications. Here, a facile strategy is proposed to construct hydrogel fibers with ultrahigh conductivity and toughness by exploiting the synergistic effects of freezing‐thawing, salting‐out, and drying‐annealing. The continuous phase separation induced by the combined processes results in hierarchical structures, promoting the formation of interconnected conductive networks and increasing the fiber's crystallinity and crystal domain size. The prepared conductive hydrogel fibers exhibited ultrahigh conductivity (≈958 S cm−1), excellent mechanical properties (strength (≈6.2 MPa), stretchability (>300%), and toughness (≈10 MJ m−2)), high water content (≈75%), outstanding water stability, and fatigue resistance properties. In addition, the processibility of conductive hydrogel yarns and fabrics are demonstrated and their potential application in bioelectronics. Overall, this work presents a preparation strategy for conductive hydrogel fibers, which will facilitate the advancement of soft electronics and may inspire structural construction in other polymers.

Cellulose-based Conductive Materials for Bioelectronics.

The growing demand for electronic devices has led to excessive stress on Earth's resources, necessitating effective waste management and the search for renewable materials with minimal environmental impact. Bioelectronics, designed to interface with the human body, have traditionally been made from inorganic materials, such as metals, which, while having suitable electrical conductivity, differ significantly in chemical and mechanical properties from biological tissues. This can cause issues such as unreliable signal collection and inflammatory responses. Recently, natural biopolymers such as cellulose, chitosan, and silk have been explored for flexible devices, given their chemical uniqueness, shape flexibility, ease of processing, mechanical strength, and biodegradability. Cellulose is the most abundant natural biopolymer, has been widely used across industries, and can be transformed into electronically conductive carbon materials. This review focuses on the advancements in cellulose-based conductive materials for bioelectronics, detailing their chemical properties, methods to enhance conductivity, and forms used in bioelectronic applications. It highlights the compatibility of cellulose with biological tissues, emphasizing its potential in developing wearable sensors, supercapacitors, and other healthcare-related devices. The review also addresses current challenges in this field and suggests future research directions to overcome these obstacles and fully realize the potential of cellulose-based bioelectronics.

Silk fibroin-based bioelectronic devices for high-sensitivity, stable, and prolonged in vivo recording

Silk fibroin, recognized for its biocompatibility and modifiable properties, has significant potential in bioelectronics. Traditional silk bioelectronic devices, however, face rapid functional losses in aqueous or in vivo environments due to high water absorption of silk fibroin, which leads to expansion, structural damage, and conductive failure. In this study, we developed a novel approach by creating oriented crystallization (OC) silk fibroin through physical modification of the silk protein. This advancement enabled the fabrication of electronic interfaces for chronic biopotential recording. A pre-stretching treatment of the silk membrane allowed for tunable molecular orientation and crystallization, markedly enhancing its aqueous stability, biocompatibility, and electronic shielding capabilities. The OC devices demonstrated robust performance in sensitive detection and motion tracking of cutaneous electrical signals, long-term (over seven days) electromyographic signal acquisition in live mice with high signal-to-noise ratio (SNR >20), and accurate detection of high-frequency oscillations (HFO) in epileptic models (200–500 Hz). This work not only improves the structural and functional integrity of silk fibroin but also extends its application in durable bioelectronics and interfaces suited for long-term physiological environments.

Polyurethane Vitrimers Engineered with Nitrogen-Coordinating Cyclic Boronic Diester Bonds for Sustainable Bioelectronics.

Flexible bioelectronic devices seamlessly interface with organs and tissues, offering unprecedented opportunity for timely prevention, early diagnosis, and medical therapies. However, the majority of flexible substrates utilized in bioelectronics still encounter significant challenges in terms of recyclability and reprocessing, leading to the accumulation of environmentally and biologically hazardous toxic waste. Here, the study reports the design of recyclable polyurethane (PU) vitrimers engineered with internal boron-nitrogen coordination bonds that can reversibly dissociate to boronic acids and hydroxyl, or undergo metathesis reaction following an associative pathway. The study demonstrates the capacity of these recyclable PU vitrimers as flexible substrates in various wearable and implantable bioelectronic applications, achieving high-quality electrophysiological recordings and stimulation. Furthermore, the study establishes a sustainable recycling process by reconstructing a range of bioelectronic devices from the recycled PU vitrimers without compromising the mechanical performance. This closed-loop approach not only addresses the critical challenge of the reclaiming medical electronic waste but also paves the way for the development of sustainable flexible bioelectronics for healthcare applications.

Cation-Dependent Mixed Ionic-Electronic Transport in a Perylenediimide Small-Molecule Semiconductor.

A rapidly growing interest in organic bioelectronic applications has spurred the development of a wide variety of organic mixed ionic-electronic conductors. While these new mixed conductors have enabled the community to interface organic electronics with biological systems and efficiently transduce biological signals (ions) into electronic signals, the current materials selection does not offer sufficient selectivity towards specific ions of biological relevance without the use of auxiliary components such as ion-selective membranes. Here, we present the molecular design of an n-type (electron-transporting) perylene diimide semiconductor material decorated with pendant oligoether groups to facilitate interactions with cations such as Na+ and K+. Using the cyclic 15-crown-5 oligoether motif, we find that the resulting mixed conductor PDI-crown displays a strong dependence on the size of the electrolyte cation when tested in an organic electrochemical transistor configuration. In stark contrast to the low current response on the order of 1 μA observed with aqueous sodium chloride, a nearly 200-fold increase in current is observed with aqueous potassium chloride. We ascribe the high selectivity to extended molecular aggregation and therefore efficient charge transport in the presence of K+ due to a favourable sandwich-like structure between two adjacent 15-crown-5 motifs and the potassium ion.

Bulk proton conduction in films from a truncated reflectin variant

Protein- and peptide-based proton-conducting biomaterials have been touted as particularly promising for bioelectronics applications because of their advantageous chemical and physical characteristics, typically excellent biocompatibilities, and readily understood electrical properties. Within this context, our laboratory has previously discovered and systematically investigated bulk proton conduction for a unique family of cephalopod structural proteins called reflectins. Herein, we leverage a combination of experimental and computational methodologies to investigate the bulk electrical properties of hierarchically nanostructured films self-assembled from a previously reported truncated reflectin variant. Our findings indicate that the truncated reflectin variant exhibits protonic conductivities and associated figures of merit on par with those reported for both full-length reflectins and other proteinaceous proton-conducting materials. The combined studies enhance current understanding of reflectins’ functional properties within the framework of bioengineering and bioelectronics applications and may ultimately facilitate the development of other protein- and peptide-based conductive biomaterials.

Molecular recognition characteristics of co-assembled peptides on atomically flat graphite surfaces

Molecular recognition, involving the binding of two or more molecules, is widely found in multiple disciplines. It plays a crucial role in driving specific molecular functionalization or biological activities such as antigen–antibody interactions. Recently, the molecular recognition of single peptides self-assembly at interfaces has been widely investigated since their broad applications in biosensors and bioelectronics. However, the recognition characteristics of peptide-peptide co-assembly on solids has not been investigated yet, which provides a basis for potential multi-probes biosensing or structure-intermingled functionalized bioelectronic applications. Here, we explored the molecular recognition characteristics of co-assembled peptides on two-dimensional (2D) layered nanomaterials, specifically graphite. Our findings showed distinct surface characteristics of peptide co-assembly in comparison to the independent peptides self-assembly. Peptide co-assembly exhibited the nucleation and growth heterogeneities with reduced nucleation and growth rates, dominated by a diffusion-limited step as confirmed via carrying out the sequential-assembled experiments. Moreover, molecular dynamics simulation reveals a slowdown binding process of co-assembled peptides to graphite. Furthermore, the misattachment of one peptide to arrays of another types of peptide with distinct structural ordering orientations severely postponed peptide elongation. Therefore, our work provides valuable insight into the fundamental surface characteristics of two co-assembled peptides as they specifically recognize graphite surface via undergoing continuous surface behaviors from binding to diffusion until final ordering process. The formation of co-assembled peptide patterns on 2D layered nanomaterials incorporates multiple functions enabling to provide potential applications in intermingled peptide-based biosensing or bioelectronic nanodevices.

Semiconductive-like Behaviour and Negative Differential Effect Observed in Self-Assembled Riboflavin Layer on Gold Electrodes

Riboflavin or vitamin B2 plays significant roles in metabolic reactions and energy production, establishing it as an important research subject in biology and medicine. While there are numerous riboflavin-related publications in these fields, interrogation of its electronic properties in relation to the physiological function at the cellular level remains obscure due to technological challenges. However, progress in molecular electronics and the discovery of the semiconductor-like behaviour of biomolecules in recent times have initiated growing interest in exploring the electronic properties of these materials for potential bioelectronic device applications. In this work, we demonstrate novel semiconductor-like behaviour in riboflavin within a gold/Riboflavin/gold Schottky junction. We observed the occurrence of two negative differential resistance peaks at low voltages of 1.5 and 2.0 V, probably the first-ever report of this effect in a biomolecule. Interestingly, the proposed mechanism simulates a single Schottky junction behaviour despite the physical existence of two junctions. Solid-state parameters such as turn-on voltage, shunt resistance, and ideality factor were also calculated using Conventional and Cheung and Cheung’s methods. The results were highly characteristic to the riboflavin studied when compared to previous works on biomolecules. This opens up the possibility of developing solid-state sensors for electronically characterising biomolecules like vitamins to help advance our understanding of the electronic properties of these essential nutrients.

High‐Performance, Single‐Component Ambipolar Organic Electrochemical Transistors with Balanced n/p‐Type Properties for Inverter and Biosensor Applications

AbstractAmbipolar organic electrochemical transistors (OECTs) with a single organic mixed ionic‐electronic conductor (OMIEC) have unique advantages by reducing fabrication complexity and cost in complementary logic circuit and bioelectronic applications. However, the design and synthesis of high‐performance ambipolar OMIECs for efficient transport and coupling both cation/anion and electron/hole remain challenging. Herein, a donor–acceptor (D–A)‐typed ambipolar OMIEC polymer (DHF‐gTT) is presented, whose superior ambipolarity stems from the concurrent oligoethyleneglycol‐functionalized D/A units that facilitates cation/anion injection and transport. Additionally, the fluorination of acceptor unit improves both hole/electron transports due to the fully‐locked backbone and promotes electron injection by down‐shifting molecular energy levels. Consequently, DHF‐gTT‐based OECTs achieve balanced figure‐of‐merit (µC*) for both p‐type and n‐type operations (12.4–14.6 F cm−1 V−1 s−1), setting new benchmarks for ambipolar OECTs, in terms of n‐type µC* and electron/hole mobilities. Such ambipolar OECTs enable the inverter to achieve a record‐high gain (102 V/V) and associated n‐type and p‐type molecular detectors to offer real‐time and highly sensitive detection of histamine and hydrogen peroxide detection, respectively. These results indicate the effectiveness of judicious molecular design on achieving high‐performance ambipolar OMIECs, allowing the state‐of‐the‐art single‐component ambipolar OECTs for both highly integrated logic circuit and bioelectronic applications.

Flexible and antibacterial conductive hydrogels based on silk fibroin/polyaniline/AgNPs for motion sensing and wound healing promotion under electrical stimulation.

Flexible conductive hydrogel-based electronic skin (E-skin) for simultaneous biotherapeutics and sensing applications is one of the current research directions. In this study, conductive and homogeneous silk fibroin/polyaniline/AgNP complexes (SPAg complexes) were prepared with the assistance of silk fibroin, which greatly optimized the compatibility of PANI with the hydrogel matrix. Then, SPAg was introduced into the covalently crosslinked polymer network to prepare poly(acrylamide-co-sulfobetaine methacrylate) - SPAg hydrogels (labeled as PSPAg hydrogels). The PSPAg hydrogels exhibit good biocompatibility, excellent mechanical properties, superb adhesive performance, and fantastic sensing capabilities. Being connected to a smartphone via a Bluetooth system, the SPAg hydrogel-based E-skin was employed to accurately monitor human movements including vigorous joint movements and subtle facial micro-expressions. Finally, benefiting from the synergistic effect of antimicrobial and exogenous electrical stimulation, through promoting angiogenesis and accelerating collagen production in diabetic wounds, PSPAg E-skin successfully facilitates rapid diabetic wound healing. Therefore, the multifunctional PSPAg hydrogel-based E-skin shows great promise for applications in wearable devices and bioelectronics.

Polymeric silk fibroin hydrogel as a conductive and multifunctional adhesive for durable skin and epidermal electronics.

Silk fibroin (SF)-based hydrogels are promising multifunctional adhesive candidates for real-world applications in tissue engineering, implantable bioelectronics, artificial muscles, and artificial skin. However, developing conductive SF-based hydrogels that are suitable for the micro-physiological environment and maintain their physical and chemical properties over long periods of use remains challenging. Herein, we developed an ion-conductive SF hydrogel composed of glycidyl methacrylate silk fibroin (SilMA) and bioionic liquid choline acylate (ChoA) polymer chains, together with the modification of acrylated thymine (ThyA) and adenine (AdeA) functional groups. The resulting polymeric ion-conductive SF composite hydrogel demonstrated high bioactivity, strong adhesion strength, good mechanical compliance, and stretchability. The formed hydrogel network of ChoA chains can coordinate with the ionic strength in the micro-physiological environment while maintaining the adaptive coefficient of expansion and stable mechanical properties. These features help to form a stable ion-conducting channel for the hydrogel. Additionally, the hydrogel network modified with AdeA and ThyA, can provide a strong adhesion to the surface of a variety of substrates, including wet tissue through abundant hydrogen bonding. The biocompatible and ionic conductive SF composite hydrogels can be easily prepared and incorporated into flexible skin or epidermal sensing devices. Therefore, our polymeric SF-based hydrogel has great potential and wide application to be an important component of many flexible electronic devices for personalized healthcare.

Low modulus hydrogel-like elastomer sensors with ultra-fast self-healing, underwater self-adhesion, high durability/stability and recyclability for bioelectronics

Flexible sensors simultaneously with property of hydrogel-like low modulus/room temperature ultra-fast self-healing and with elastomer-like durability /environmental stability and underwater adhesion for bioelectronics has not been reported. A low modulus hydrogel-like elastomer that achieves ultrafast self-healing through molecular chain entanglement at room temperature was prepared based on furfuryl alcohol-modified poly(sebacate glyceride) (PGS) prepolymer, furfuryl alcohol-modified poly(ionic liquid) and bismaleimide by Diels-Alder (DA) reaction. The conductive elastomer-based flexible sensors exhibit hydrogel-like properties of low modulus (6.41 kPa) and ultra-fast self-healing (98 % self-healing efficiency within 5 s). The elastomer also possesses rapid subzero and underwater self-healing properties within 5 s. Moreover, PGS-0.2DA-0.2PIL exhibits pressure sensitive adhesive properties and can be adhered/re-adhered in water. The flexible sensor shows elastomer-like high durability, high environmental stability, multiple recyclability and reusability, and it exhibits wide detection ranges, fast response time, low hysteresis, anti-freezing, anti-bacterial and good biocompatibility. The flexible sensors can accurately identify micro-expressions/eye rotation, monitor human movement/health, detect ECG/EMG signals and control robotic arm movements. In conclusion, a new strategy for design of hydrogel-like conductive elastomers via molecular structure design is proposed, and the elastomers-based flexible sensors with low modulus, rapid self-healing and durability/environmental stability show great promising for bioelectronic applications.

Tailor-Made Gold Nanomaterials for Applications in Soft Bioelectronics and Optoelectronics.

In modern nanoscience and nanotechnology, gold nanomaterials are indispensable building blocks that have demonstrated a plethora of applications in catalysis, biology, bioelectronics, and optoelectronics. Gold nanomaterials possess many appealing material properties, such as facile control over their size/shape and surface functionality, intrinsic chemical inertness yet with high biocompatibility, adjustable localized surface plasmon resonances, tunable conductivity, wide electrochemical window, etc. Such material attributes have been recently utilized for designing and fabricating soft bioelectronics and optoelectronics. This motivates to give a comprehensive overview of this burgeoning field. The discussion of representative tailor-made gold nanomaterials, including gold nanocrystals, ultrathin gold nanowires, vertically aligned gold nanowires, hard template-assisted gold nanowires/gold nanotubes, bimetallic/trimetallic gold nanowires, gold nanomeshes, and gold nanosheets, is begun. This is followed by the description of various fabrication methodologies for state-of-the-art applications such as strain sensors, pressure sensors, electrochemical sensors, electrophysiological devices, energy-storage devices, energy-harvesting devices, optoelectronics, and others. Finally, the remaining challenges and opportunities are discussed.

Engineering Lipid-Based Pop-up Conductive Interfaces with PEDOT:PSS and Light-Responsive Azopolymer Films.

Significant challenges have emerged in the development of biomimetic electronic interfaces capable of dynamic interaction with living organisms and biological systems, including neurons, muscles, and sensory organs. Yet, there remains a need for interfaces that can function on demand, facilitating communication and biorecognition with living cells in bioelectronic systems. In this study, the design and engineering of a responsive and conductive material with cell-instructive properties, allowing for the modification of its topography through light irradiation, resulting in the formation of "pop-up structures", is presented. A deformable substrate, composed of a bilayer comprising a light-responsive, azobenzene-containing polymer, pDR1m, and a conductive polymer, PEDOT:PSS, is fabricated and characterized. Moreover, the successful formation of supported lipid bilayers (SLBs) and the maintenance of integrity while deforming the pDR1m/PEDOT:PSS films represent promising advancements for future applications in responsive bioelectronics and neuroelectronic interfaces.

Multifunctional Natural and Synthetic Melanin for Bioelectronic Applications: A Review.

Emerging material interest in bioelectronic applications has highlighted natural melanin and its derivatives as promising alternatives to conventional synthetic conductors. These materials, traditionally noted for their adhesive, antioxidant, biocompatible, and biodegradable properties, have barely been used as conductors due to their extremely low electrical activities. However, recent studies have demonstrated good conductive properties in melanin materials that promote electronic-ionic hybrid charge transfer, attributed to the formation of an extended conjugated backbone. This review examines the multifunctional properties of melanin materials, focusing on their chemical and electrochemical synthesis and their resulting structure-property-function relationship. The wide range of bioelectronic applications will also be presented to highlight their importance and potential to expand into new design concepts for high-performance electronic functional materials. The review concludes by addressing the current challenges in utilizing melanin for biodegradable bioelectronics, providing a perspective on future developments.

Invoking Ultralong Organic Phosphorescence by Locking Dimeric Chromophores Through Multiple Hydrogen Bonding

AbstractUltralong organic phosphorescence (UOP) is essential for potential applications in bioelectronics and optoelectronics. However, the precise design of UOP materials remains a formidable challenge. Herein, a facile strategy is presented to confine dimeric chromophores for triggering UOP emission, based on the manipulation of the carbonyl, sulfonyl, and amino groups within organic phosphors. The experimental data reveal that saccharin analogs in crystals containing dimeric chromophores, confined by the (3D) hydrogen‐bonded networks, exhibit ultralong emission lifetime of up to 635 ms under ambient conditions. Whereas for saccharin analogue crystals lacking dimeric chromophores, the lifetime decreases to 54 ms, resulting in the absence of UOP emission. Moreover, the non‐toxic saccharin crystals with UOP have succeeded in drug anti‐counterfeiting. These findings will open a novel avenue for the design UOP materials and broaden the domain of UOP to diverse applications.

Highly Sensitive Biosensors Based on All-PEDOT:PSS Organic Electrochemical Transistors with Laser-Induced Micropatterning.

Recent advances in numerous biological applications have increased the accuracy of monitoring the level of biologically significant analytes in the human body to manage personal nutrition and physiological conditions. However, despite promising reports about costly wearable devices with high sensing performance, there has been a growing demand for inexpensive sensors that can quickly detect biological molecules. Herein, we present highly sensitive biosensors based on organic electrochemical transistors (OECTs), which are types of organic semiconductor-based sensors that operate consistently at low operating voltages in aqueous solutions. Instead of the gold or platinum electrode used in current electrochemical devices, poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) was used as both the channel and gate electrodes in the OECT. Additionally, to overcome the patterning resolution limitations of conventional solution processing, we confirmed that the irradiation of a high-power IR laser (λ = 1064 nm) onto the coated PEDOT:PSS film was able to produce spatially resolvable micropatterns in a digital-printing manner. The proposed patterning technique exhibits high suitability for the fabrication of all-PEDOT:PSS OECT devices. The device geometry was optimized by fine-tuning the gate area and the channel-to-gate distance. Consequently, the sensor for detecting ascorbic acid (vitamin C) concentrations in an electrolyte exhibited the best sensitivity of 125 μA dec-1 with a limit of detection of 1.3 μM, which is nearly 2 orders of magnitude higher than previous findings. Subsequently, an all-plastic flexible epidermal biosensor was established by transferring the patterned all-PEDOT:PSS OECT from a glass substrate to a PET substrate, taking full advantage of the flexibility of PEDOT:PSS. The prepared all-plastic sensor device is highly cost-effective and suitable for single-use applications because of its acceptable sensing performance and reliable signal for detecting vitamin C. Additionally, the epidermal sensor successfully obtained the temporal profile of vitamin C in the sweat of a human volunteer after the consumption of vitamin C drinks. We believe that the highly sensitive all-PEDOT:PSS OECT device fabricated using the accurate patterning process exhibits versatile potential as a low-cost and single-use biosensor for emerging bioelectronic applications.

Improving the air stability of flexible top-emitting organic light-emitting diodes

Flexible organic light-emitting diodes (OLEDs) are promising light sources for biomedical applications. However, the use of these flexible devices has been restricted by their short shelf lifetimes due to poor ambient stability. Here, the fabrication of a long-lived flexible OLED is reported by replacing air-sensitive metals such as aluminum, and alkali metals used as n dopants, with silver. In addition, to achieve stable and efficient flexible OLEDs we tuned the optical cavity length to the second-order interference maximum. The device design has simple encapsulation and leads to an improvement in the air stability of flexible OLEDs which show a shelf lifetime of greater than 130 days whereas the conventional structure exhibits degradation after only 12 days. The proposed design for making flexible OLEDs demonstrates a great potential for using the devices for wearable bioelectronic applications.