All Publications

  • Enhancement-Mode PEDOT:PSS Organic Electrochemical Transistors Using Molecular De-Doping. Advanced materials (Deerfield Beach, Fla.) Keene, S. T., van der Pol, T. P., Zakhidov, D., Weijtens, C. H., Janssen, R. A., Salleo, A., van de Burgt, Y. 2020: e2000270


    Organic electrochemical transistors (OECTs) show great promise for flexible, low-cost, and low-voltage sensors for aqueous solutions. The majority of OECT devices are made using the polymer blend poly(ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), in which PEDOT is intrinsically doped due to inclusion of PSS. Because of this intrinsic doping, PEDOT:PSS OECTs generally operate in depletion mode, which results in a higher power consumption and limits stability. Here, a straightforward method to de-dope PEDOT:PSS using commercially available amine-based molecular de-dopants to achieve stable enhancement-mode OECTs is presented. The enhancement-mode OECTs show mobilities near that of pristine PEDOT:PSS (2 cm2 V-1 s-1 ) with stable operation over 1000 on/off cycles. The electron and proton exchange among PEDOT, PSS, and the molecular de-dopants are characterized to reveal the underlying chemical mechanism of the threshold voltage shift to negative voltages. Finally, the effect of the de-doping on the microstructure of the spin-cast PEDOT:PSS films is investigated.

    View details for DOI 10.1002/adma.202000270

    View details for PubMedID 32202010

  • Lowering the threshold for bioelectronics. Nature materials Keene, S., van de Burgt, Y. 2020

    View details for DOI 10.1038/s41563-020-0623-x

    View details for PubMedID 32203455

  • A biohybrid synapse with neurotransmitter-mediated plasticity. Nature materials Keene, S. T., Lubrano, C., Kazemzadeh, S., Melianas, A., Tuchman, Y., Polino, G., Scognamiglio, P., Cinà, L., Salleo, A., van de Burgt, Y., Santoro, F. 2020


    Brain-inspired computing paradigms have led to substantial advances in the automation of visual and linguistic tasks by emulating the distributed information processing of biological systems1. The similarity between artificial neural networks (ANNs) and biological systems has inspired ANN implementation in biomedical interfaces including prosthetics2 and brain-machine interfaces3. While promising, these implementations rely on software to run ANN algorithms. Ultimately, it is desirable to build hardware ANNs4,5 that can both directly interface with living tissue and adapt based on biofeedback6,7. The first essential step towards biologically integrated neuromorphic systems is to achieve synaptic conditioning based on biochemical signalling activity. Here, we directly couple an organic neuromorphic device with dopaminergic cells to constitute a biohybrid synapse with neurotransmitter-mediated synaptic plasticity. By mimicking the dopamine recycling machinery of the synaptic cleft, we demonstrate both long-term conditioning and recovery of the synaptic weight, paving the way towards combining artificial neuromorphic systems with biological neural networks.

    View details for DOI 10.1038/s41563-020-0703-y

    View details for PubMedID 32541935

  • Parallel programming of an ionic floating-gate memory array for scalable neuromorphic computing SCIENCE Fuller, E. J., Keene, S. T., Melianas, A., Wang, Z., Agarwal, S., Li, Y., Tuchman, Y., James, C. D., Marinella, M. J., Yang, J., Salleo, A., Talin, A. 2019; 364 (6440): 570-+
  • Mechanisms for Enhanced State Retention and Stability in Redox-Gated Organic Neuromorphic Devices ADVANCED ELECTRONIC MATERIALS Keene, S., Melianas, A., van de Burgt, Y., Salleo, A. 2019; 5 (2)
  • Multifunctional, Room-Temperature Processable, Heterogeneous Organic Passivation Layer for Oxide Semiconductor Thin-Film Transistors. ACS applied materials & interfaces Tak, Y. J., Keene, S. T., Kang, B. H., Kim, W. G., Kim, S. J., Salleo, A., Kim, H. J. 2019


    In recent decades, oxide thin-film transistors (TFTs) have attracted a great deal of attention as a promising technology in terms of next-generation electronics due to their outstanding electrical performance. However, achieving robust electrical characteristics under various environments is a crucial challenge for successful realization of oxide-based electronic applications. To resolve the limitation, we propose a highly flexible and reliable heterogeneous organic passivation layer composed of stacked parylene-C and diketopyrrolopyrrole-polymer films for improving stability of oxide TFTs under various environments and mechanical stress. The presented multifunctional heterogeneous organic (MHO) passivation leads to high-performance oxide TFTs by: (1) improving their electrical characteristics, (2) protecting them from external reactive molecules, and (3) blocking light exposure to the oxide layer. As a result, oxide TFTs with MHO passivation exhibit outstanding stability in ambient air as well as under light illumination: the threshold voltage shift of the device is almost 0 V under severe negative bias illumination stress condition (white light of 5700 lx, gate voltage of -20 V, and drain voltage of 10.1 V for 20 000 s). Furthermore, since the MHO passivation layer exhibits high mechanical stability at a bending radius of ≤5 mm and can be deposited at room temperature, this technique is expected to be useful in the fabrication of flexible/wearable devices.

    View details for DOI 10.1021/acsami.9b16898

    View details for PubMedID 31850727

  • The Mechanism of Dedoping PEDOT:PSS by Aliphatic Polyamines. The journal of physical chemistry. C, Nanomaterials and interfaces van der Pol, T. P., Keene, S. T., Saes, B. W., Meskers, S. C., Salleo, A., van de Burgt, Y., Janssen, R. A. 2019; 123 (39): 24328–37


    Poly(3,4-ethylenedioxythiophene) blended with polystyrenesulfonate and poly(styrenesulfonic acid), PEDOT:PSS, has found widespread use in organic electronics. Although PEDOT:PSS is commonly used in its doped electrically conducting state, the ability to efficiently convert PEDOT:PSS to its undoped nonconducting state is of interest for a wide variety of applications ranging from biosensors to organic neuromorphic devices. Exposure to aliphatic monoamines, acting as an electron donor and Brønsted-Lowry base, has been reported to be partly successful, but monoamines are unable to fully dedope PEDOT:PSS. Remarkably, some-but not all-polyamines can dedope PEDOT:PSS very efficiently to very low conductivity levels, but the exact chemical mechanism involved is not understood. Here, we study the dedoping efficacy of 21 different aliphatic amines. We identify the presence of two or more primary amines, which can participate in an intramolecular reaction, as the key structural motif that endows polyamines with high PEDOT:PSS dedoping strength. A multistep reaction mechanism, involving sequential electron transfer and deprotonation steps, is proposed that consistently explains the experimental results. Finally, we provide a simple method to convert the commonly used aqueous PEDOT:PSS dispersion into a precursor formulation that forms fully dedoped PEDOT:PSS films after spin coating and subsequent thermal annealing.

    View details for DOI 10.1021/acs.jpcc.9b07718

    View details for PubMedID 31602285

    View details for PubMedCentralID PMC6778972

  • Wearable Organic Electrochemical Transistor Patch for Multiplexed Sensing of Calcium and Ammonium Ions from Human Perspiration. Advanced healthcare materials Keene, S. T., Fogarty, D., Cooke, R., Casadevall, C. D., Salleo, A., Parlak, O. 2019: e1901321


    Wearable health monitoring has garnered considerable interest from the healthcare industry as an evolutionary alternative to standard practices with the ability to provide rapid, off-site diagnosis and patient-monitoring. In particular, sweat-based wearable biosensors offer a noninvasive route to continuously monitor a variety of biomarkers for a range of physiological conditions. Both the accessibility and wealth of information of sweat make it an ideal target for noninvasive devices that can aid in early diagnosis of disease or to monitor athletic performance. Here, the integration of ammonium (NH4+ ) and calcium (Ca2+ ) ion-selective membranes with a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)-based (PEDOT:PSS) organic electrochemical transistor (OECT) for multiplexed sensing of NH4+ and Ca2+ in sweat with high sensitivity and selectivity is reported for the first time. The presented wearable sweat sensor is designed by combining a flexible and stretchable styrene-ethylene-butene-styrene substrate with a laser-patterned microcapillary channel array for direct sweat acquisition and delivery to the ion-selective OECT. The resulting dermal sensor exhibits a wide working range between 0.01 × 10-3 and 100 × 10-3 m, well within the physiological levels of NH4+ and Ca2+ in sweat. The integrated devices are successfully implemented with both ex situ measurements and on human subjects with real-time analysis using a wearable sensor assembly.

    View details for DOI 10.1002/adhm.201901321

    View details for PubMedID 31714014

  • Parallel programming of an ionic floating-gate memory array for scalable neuromorphic computing. Science (New York, N.Y.) Fuller, E. J., Keene, S. T., Melianas, A., Wang, Z., Agarwal, S., Li, Y., Tuchman, Y., James, C. D., Marinella, M. J., Yang, J. J., Salleo, A., Talin, A. A. 2019


    Neuromorphic computers could overcome efficiency bottlenecks inherent to conventional computing through parallel programming and read out of artificial neural network weights in a crossbar memory array. However, selective and linear weight updates and <10 nanoampere read currents are required for learning that surpasses conventional computing efficiency. We introduce an ionic floating-gate memory (IFG) array based upon a polymer redox transistor connected to a conductive-bridge memory (CBM). Selective and linear programming of a transistor array is executed in parallel by overcoming the bridging voltage threshold of the CBMs. Synaptic weight read-out with currents <10 nanoampere is achieved by diluting the conductive polymer in an insulating channel to decrease the conductance. The redox transistors endure >1 billion 'read-write' operations and support >1 megahertz 'read-write' frequencies.

    View details for PubMedID 31023890

  • High-Throughput Open-Air Plasma Activation of Metal-Oxide Thin Films with Low Thermal Budget ACS APPLIED MATERIALS & INTERFACES Tak, Y., Hilt, F., Keene, S., Kim, W., Dauskardt, R. H., Salleo, A., Kim, H. 2018; 10 (43): 37223–32


    Sputter-processed oxide films are typically annealed at high temperature (activation process) to achieve stable electrical characteristics through the formation of strong metal-oxide chemical bonds. For instance, indium-gallium-zinc oxide (IGZO) films typically need a thermal treatment at 300 °C for ≥1 h as an activation process. We propose an open-air plasma treatment (OPT) to rapidly and effectively activate sputter-processed IGZO films. The OPT effectively induces metal-oxide chemical bonds in IGZO films at temperatures as low as 240 °C, with a dwell time on the order of a second. Furthermore, by controlling the plasma-processing conditions (scan speed, distance a between plasma nozzle and samples, and gas flow rate), the electrical characteristics and the microstructure of the IGZO films can be easily tuned. Finally, OPT can be utilized to implement a selective activation process. Plasma-treated IGZO thin-film transistors (TFTs) exhibit comparable electrical characteristics to those of conventionally thermal treated IGZO TFTs. Through in-depth optical, chemical, and physical characterizations, we confirm that OPT simultaneously dissociates weak chemical bonds by UV radiation and ion bombardment and re-establishes the metal-oxide network by radical reaction and OPT-induced heat.

    View details for PubMedID 30288973

  • Molecularly selective nanoporous membrane-based wearable organic electrochemical device for noninvasive cortisol sensing. Science advances Parlak, O., Keene, S. T., Marais, A., Curto, V. F., Salleo, A. 2018; 4 (7): eaar2904


    Wearable biosensors have emerged as an alternative evolutionary development in the field of healthcare technology due to their potential to change conventional medical diagnostics and health monitoring. However, a number of critical technological challenges including selectivity, stability of (bio)recognition, efficient sample handling, invasiveness, and mechanical compliance to increase user comfort must still be overcome to successfully bring devices closer to commercial applications. We introduce the integration of an electrochemical transistor and a tailor-made synthetic and biomimetic polymeric membrane, which acts as a molecular memory layer facilitating the stable and selective molecular recognition of the human stress hormone cortisol. The sensor and a laser-patterned microcapillary channel array are integrated in a wearable sweat diagnostics platform, providing accurate sweat acquisition and precise sample delivery to the sensor interface. The integrated devices were successfully used with both ex situ methods using skin-like microfluidics and on human subjects with on-body real-sample analysis using a wearable sensor assembly.

    View details for PubMedID 30035216

  • Optimized pulsed write schemes improve linearity and write speed for low-power organic neuromorphic devices JOURNAL OF PHYSICS D-APPLIED PHYSICS Keene, S. T., Melianas, A., Fuller, E. J., van de Burgt, Y., Talin, A., Salleo, A. 2018; 51 (22)
  • Organic Electronics for Neuromorphic Computing NATURE ELECTRONICS Burgt, Y. v., Melianas, A., Keene, S. T., Malliaras, G., Salleo, A. 2018; 1 (7): 386-397
  • Enhanced Cell-Chip Coupling by Rapid Femtosecond Laser Patterning of Soft PEDOT:PSS Biointerfaces ACS APPLIED MATERIALS & INTERFACES Santoro, F., van de Burgt, Y., Keene, S., Cui, B., Salleo, A. 2017; 9 (45): 39116–21


    Interfacing soft materials with biological systems holds considerable promise for both biosensors and recording live cells. However, the interface between cells and organic substrates is not well studied, despite its crucial role in the effectiveness of the device. Furthermore, well-known cell adhesion enhancers, such as microgrooves, have not been implemented on these surfaces. Here, we present a nanoscale characterization of the cell-substrate interface for 3D laser-patterned organic electrodes by combining electrochemical impedance spectroscopy (EIS) and scanning electron microscopy/focused ion beam (SEM/FIB). We demonstrate that introducing 3D micropatterned grooves on organic surfaces enhances the cell adhesion of electrogenic cells.

    View details for DOI 10.1021/acsami.7b12308

    View details for Web of Science ID 000416203800003

    View details for PubMedID 29083144

  • Hierarchical Aerographite nano-microtubular tetrapodal networks based electrodes as lightweight supercapacitor NANO ENERGY Parlak, O., Mishra, Y. K., Grigoriev, A., Mecklenburg, M., Luo, W., Keene, S., Salleo, A., Schulte, K., Ahuja, R., Adelung, R., Turner, A. P., Tiwari, A. 2017; 34: 570-577
  • A non-volatile organic electrochemical device as a low-voltage artificial synapse for neuromorphic computing. Nature materials van de Burgt, Y., Lubberman, E., Fuller, E. J., Keene, S. T., Faria, G. C., Agarwal, S., Marinella, M. J., Alec Talin, A., Salleo, A. 2017


    The brain is capable of massively parallel information processing while consuming only ∼1-100 fJ per synaptic event. Inspired by the efficiency of the brain, CMOS-based neural architectures and memristors are being developed for pattern recognition and machine learning. However, the volatility, design complexity and high supply voltages for CMOS architectures, and the stochastic and energy-costly switching of memristors complicate the path to achieve the interconnectivity, information density, and energy efficiency of the brain using either approach. Here we describe an electrochemical neuromorphic organic device (ENODe) operating with a fundamentally different mechanism from existing memristors. ENODe switches at low voltage and energy (<10 pJ for 10(3) μm(2) devices), displays >500 distinct, non-volatile conductance states within a ∼1 V range, and achieves high classification accuracy when implemented in neural network simulations. Plastic ENODes are also fabricated on flexible substrates enabling the integration of neuromorphic functionality in stretchable electronic systems. Mechanical flexibility makes ENODes compatible with three-dimensional architectures, opening a path towards extreme interconnectivity comparable to the human brain.

    View details for DOI 10.1038/nmat4856

    View details for PubMedID 28218920

  • Electronic control of H+ current in a bioprotonic device with Gramicidin A and Alamethicin NATURE COMMUNICATIONS Hemmatian, Z., Keene, S., Josberger, E., Miyake, T., Arboleda, C., Soto-Rodriguez, J., Baneyx, F., Rolandi, M. 2016; 7: 12981


    In biological systems, intercellular communication is mediated by membrane proteins and ion channels that regulate traffic of ions and small molecules across cell membranes. A bioelectronic device with ion channels that control ionic flow across a supported lipid bilayer (SLB) should therefore be ideal for interfacing with biological systems. Here, we demonstrate a biotic-abiotic bioprotonic device with Pd contacts that regulates proton (H+) flow across an SLB incorporating the ion channels Gramicidin A (gA) and Alamethicin (ALM). We model the device characteristics using the Goldman-Hodgkin-Katz (GHK) solution to the Nernst-Planck equation for transport across the membrane. We derive the permeability for an SLB integrating gA and ALM and demonstrate pH control as a function of applied voltage and membrane permeability. This work opens the door to integrating more complex H+ channels at the Pd contact interface to produce responsive biotic-abiotic devices with increased functionality.

    View details for PubMedID 27713411

  • Proton mediated control of biochemical reactions with bioelectronic pH modulation. Scientific reports Deng, Y., Miyake, T., Keene, S., Josberger, E. E., Rolandi, M. 2016; 6: 24080-?


    In Nature, protons (H(+)) can mediate metabolic process through enzymatic reactions. Examples include glucose oxidation with glucose dehydrogenase to regulate blood glucose level, alcohol dissolution into carboxylic acid through alcohol dehydrogenase, and voltage-regulated H(+) channels activating bioluminescence in firefly and jellyfish. Artificial devices that control H(+) currents and H(+) concentration (pH) are able to actively influence biochemical processes. Here, we demonstrate a biotransducer that monitors and actively regulates pH-responsive enzymatic reactions by monitoring and controlling the flow of H(+) between PdHx contacts and solution. The present transducer records bistable pH modulation from an "enzymatic flip-flop" circuit that comprises glucose dehydrogenase and alcohol dehydrogenase. The transducer also controls bioluminescence from firefly luciferase by affecting solution pH.

    View details for DOI 10.1038/srep24080

    View details for PubMedID 27052724

    View details for PubMedCentralID PMC4823714

  • An enzyme logic bioprotonic transducer APL MATERIALS Miyake, T., Josberger, E. E., Keene, S., Deng, Y., Rolandi, M. 2015; 3 (1)

    View details for DOI 10.1063/1.4900886

    View details for Web of Science ID 000348995000010

  • Taking electrons out of bioelectronics: bioprotonic memories, transistors, and enzyme logic JOURNAL OF MATERIALS CHEMISTRY C Hemmatian, Z., Miyake, T., Deng, Y., Josberger, E. E., Keene, S., Kautz, R., Zhong, C., Jin, J., Rolandi, M. 2015; 3 (25): 6407-6412

    View details for DOI 10.1039/c5tc00502g

    View details for Web of Science ID 000356529100002