- Mechanisms for Enhanced State Retention and Stability in Redox-Gated Organic Neuromorphic Devices ADVANCED ELECTRONIC MATERIALS 2019; 5 (2)
The Mechanism of Dedoping PEDOT:PSS by Aliphatic Polyamines.
The journal of physical chemistry. C, Nanomaterials and interfaces
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
Parallel programming of an ionic floating-gate memory array for scalable neuromorphic computing.
Science (New York, N.Y.)
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
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.
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 2018; 51 (22)
Organic Electronics for Neuromorphic Computing
2018; 1 (7): 386-397
View details for DOI 10.1038/s41928-018-0103-3
Enhanced Cell-Chip Coupling by Rapid Femtosecond Laser Patterning of Soft PEDOT:PSS Biointerfaces
ACS APPLIED MATERIALS & INTERFACES
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 2017; 34: 570-577
A non-volatile organic electrochemical device as a low-voltage artificial synapse for neuromorphic computing.
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
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.
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 2015; 3 (1)
- Taking electrons out of bioelectronics: bioprotonic memories, transistors, and enzyme logic JOURNAL OF MATERIALS CHEMISTRY C 2015; 3 (25): 6407-6412