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Materials GOx immobilization Km app / mM Ref. PVA-g-P(4-VP) films Physical entrapment 19 1 Nafion film Covalent attachment with GA, BSA and Nafion 14.91 2 Chitosan matrix Covalent attachment with GA in a 5% (v/v) glycerol solution 14.2 3 NiO modified glassy carbon electrodes Co-deposition with NiO nanoparticles at 0.8 V for 15 min in buffer solution 2.7 4 Gold nanoparticles Thiol-Cystamine modification of Au with IO4oxidized GOx 4.3

Conjugated polymers that support mixed (electronic and ionic) conduction are in demand for applications spanning from bioelectronics to energy harvesting and storage. To design polymer mixed conductors for high‐performance electrochemical devices, relationships between the chemical structure, charge transport, and morphology must be established. A polymer series bearing the same p‐type conjugated backbone with increasing percentage of hydrophilic, ethylene glycol side chains is synthesized, and their performance in aqueous electrolyte gated organic electrochemical transistors (OECTs) is studied. By using device physics principles and electrochemical analyses, a direct relationship is found between the OECT performance and the balanced mixed conduction. While hydrophilic side chains are required to facilitate ion transport—thus enabling OECT operation—swelling of the polymer is not de facto beneficial for balancing mixed conduction. It is shown that heterogeneous water uptake disrupts the electronic conductivity of the film, leading to OECTs with lower transconductance and slower response times. The combination of in situ electrochemical and structural techniques shown here contributes to the establishment of the structure–property relations necessary to improve the performance of polymer mixed conductors and subsequently of OECTs.

This work highlights the role of PEDOT:PSS composition in determining the efficiency of coupling between ionic and electronic charges.

From established to emergent technologies, doping plays a crucial role in all semiconducting devices. Doping could, theoretically, be an excellent technique for improving repressively low transconductances in n-type organic electrochemical transistorscritical for advancing logic circuits for bioelectronic and neuromorphic technologies. However, the technical challenge is extreme: n-doped polymers are unstable in electrochemical transistor operating environments, air and water (electrolyte). Here, the first demonstration of doping in electron transporting organic electrochemical transistors is reported. The ammonium salt tetra-nbutylammonium fluoride is simply admixed with the conjugated polymer poly(N,N'-bis(7glycol)-naphthalene-1,4,5,8-bis(dicarboximide)-co-2,2'-bithiophene-coN ,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide), and found to act as a simultaneous molecular dopant and morphology-additive. The combined effects enhance the n-type transconductance with improved channel capacitance and mobility. Furthermore, operational and shelflife stability measurements showcase the first example of water-stable n-doping in a polymer. Overall, the results set a precedent for doping/additives to impact organic electrochemical transistors as powerfully as they have in other semiconducting devices.

Inexpensive and easy-to-use diagnostic tools for fast health screening are imperative, especially in the developing world, where portability and affordability are a necessity. Accurate monitoring of metabolite levels can provide useful information regarding key metabolic activities of the body and detect the concomitant irregularities such as in the case of diabetes, a worldwide chronic disease. Today, the majority of daily glucose monitoring tools rely on piercing the skin to draw blood. The pain and discomfort associated with finger pricking have created a global need to develop non-invasive, portable glucose assays. In this work, we develop a disposable analytical device which can measure physiologically relevant glucose concentrations in human saliva based on enzymatic electrochemical detection. We use inkjet-printing technology for the rapid and low-cost deposition of all the components of this glucose sensor, from the electronics to the biorecognition elements, on commercially available paper substrates. The only electronic component of the sensor is the conducting polymer poly(3,4 ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS), while the biorecognition element comprises of the enzyme glucose oxidase coupled with an electron mediator. We demonstrate that one month after its fabrication and storage in air-free environment, the sensor maintains its function with only minor performance loss. This fully printed, all-polymer biosensor with its ease of fabrication, accuracy, sensitivity and compatibility with easy-to-obtain biofluids such as saliva aids in the development of next generation low-cost, noninvasive, eco-friendly, and disposable diagnostic tools.

Alkali-metal ions are the messengers of all living cells, governing a cascade of physiological processes through the action of ion channels. Sodium (Na +) and potassium (K +) are the two alkali metals found in human blood serum. Devices that can monitor, in real time, the concentrations of these cations in aqueous media are in demand not only for the study of cellular machinery and dysfunctions, but also to detect conditions in the human body that lead to electrolyte imbalance, such as hypernatremia, hyperkalemia or dehydration. In this work, we developed conducting polymers that respond rapidly and selectively to varying concentrations of Na + and K + in aqueous media. These polymer films, bearing crown-ether-functionalized thiophene units specific to either Na + or K + ions, generated an electrical output proportional to the cation type and concentration. Using electropolymerization, we deposited the ion-selective polymers onto microscale gold patterns and integrated them as the gate electrode of an organic electrochemical transistor (OECT). The OECT current changed with respect to the concentration of the ion to which the polymer electrode was selective. Designed as a single, miniaturized chip, the OECT enabled the selective detection of Na + and K + within a physiologically relevant range. These electrochemical ion sensors required neither a complex functionalization route to fabricate, nor ion-selective membranes or a reference electrode to operate. Such customized conducting polymers have the potential to surpass existing technologies for the detection of alkali-metal ions in aqueous media and for further development into implantable medical devices.

Alzheimer’s disease (AD) is a neurodegenerative disorder associated with a severe loss in thinking, learning, and memory functions of the brain. To date, no specific treatment has been proven to cure AD, with the early diagnosis being vital for mitigating symptoms. A common pathological change found in AD-affected brains is the accumulation of a protein named amyloid-β (Aβ) into plaques. In this work, we developed a micron-scale organic electrochemical transistor (OECT) integrated with a microfluidic platform for the label-free detection of Aβ aggregates in human serum. The OECT channel–electrolyte interface was covered with a nanoporous membrane functionalized with Congo red (CR) molecules showing a strong affinity for Aβ aggregates. Each aggregate binding to the CR-membrane modulated the vertical ion flow toward the channel, changing the transistor characteristics. Thus, the device performance was not limited by the solution ionic strength nor did it rely on Faradaic reactions or conformational changes of bioreceptors. The high transconductance of the OECT, the precise porosity of the membrane, and the compactness endowed by the microfluidic enabled the Aβ aggregate detection over eight orders of magnitude wide concentration range (femtomolar–nanomolar) in 1 μL of human serum samples. We expanded the operation modes of our transistors using different channel materials and found that the accumulation-mode OECTs displayed the lowest power consumption and highest sensitivities. Ultimately, these robust, low-power, sensitive, and miniaturized microfluidic sensors helped to develop point-of-care tools for the early diagnosis of AD.