A proton-injecting technique for the measurement of hydration-dependent protonic conductivity

Effects of proton conduction on dielectric properties of peptides

Peptides have been overlooked for their use in the field of electronics, even though they are one of the most commonly found bio-induced materials, and are not only easy to mass-produce but also exhibit a high dielectric constant. Additionally, unlike proteins, which are gaining considerable interest with materials researchers, peptides are much simpler, rendering their original characteristics easier to maintain without significant alteration of their structure. On the other hand, proteins tend to deform due to their susceptibility to environmental changes. Combining such superb dielectric properties with their relatively stable nature, peptides could be utilized as a component of electronic devices ranging from basic capacitors to more complex thin-film transistors. In this paper, a peptide chain (YYACAYY) composed of tyrosine, alanine, and cysteine was extensively studied using an impedance analyzer to determine its innate charge movement mechanism in order to extend our understanding of the electric properties of peptides. The movement of mobile protons inside the peptide insulator was found to be the source of the high relative permittivity of the peptide insulator, and the dielectric constant of the peptide insulator was found to be over 17 in humid conditions. By widening the understanding of the dielectric properties of the peptide insulator, it is expected that the peptide can be further utilized as an insulator in various electronic devices.

An optically-gated AuNP-DNA protonic transistor

Bio-interface transistors, which manipulate the transportation of ions (i.e. protons), play an important role in bridging physical devices with biological functionalities, because electrical signals are carried by ions/protons in biological systems. All available ionic transistors use electrostatic gates to tune the ionic carrier density, which requires complicated interconnect wires. In contrast, an optical gate, which offers the advantages of remote control as well as multiple light wavelength selections, has never been explored for ionic devices. Here, we demonstrate a light-gated protonic transistor fabricated from an Au nanoparticle and DNA (AuNP-DNA) hybrid membrane. The device can be turned on and off completely by using light, with a high on/off current ratio of up to 2 orders of magnitude. Moreover, the device only responds to specific light wavelengths due to the plasmonic effect from the AuNPs, which enables the capability of wavelength selectivity. Our results open up new avenues for exploring remotely controlled ionic circuits, in vivo protonic switches, and other biomedical applications.

Grotthuss mechanisms: from proton transport in proton wires to bioprotonic devices

In 1804, Theodore von Grotthuss proposed a mechanism for proton (H(+)) transport between water molecules that involves the exchange of a covalent bond between H and O with a hydrogen bond. This mechanism also supports the transport of OH(-) as a proton hole and is essential in explaining proton transport in intramembrane proton channels. Inspired by the Grotthuss mechanism and its similarity to electron and hole transport in semiconductors, we have developed semiconductor type devices that are able to control and monitor a current of H(+) as well as OH(-) in hydrated biopolymers. In this topical review, we revisit these devices that include protonic diodes, complementary, transistors, memories and transducers as well as a phenomenological description of their behavior that is analogous to electronic semiconductor devices.

Production and electrical characterization of the reflectin A2 isoform from Doryteuthis (Loligo) pealeii

​We report an improved methodology for the production of cephalopod proteins known as reflectins. Our findings may afford new opportunities for the study of these proteins’ multifaceted materials properties.

Two-terminal protonic devices with synaptic-like short-term depression and device memory

Two-terminal protonic devices with PdHx proton conducting contacts and a Nafion channel achieve 25 ms spiking, short term depression, and low-energy memory switching.

H+-type and OH- -type biological protonic semiconductors and complementary devices

Proton conduction is essential in biological systems. Oxidative phosphorylation in mitochondria, proton pumping in bacteriorhodopsin, and uncoupling membrane potentials by the antibiotic Gramicidin are examples. In these systems, H(+) hop along chains of hydrogen bonds between water molecules and hydrophilic residues - proton wires. These wires also support the transport of OH(-) as proton holes. Discriminating between H(+) and OH(-) transport has been elusive. Here, H(+) and OH(-) transport is achieved in polysaccharide- based proton wires and devices. A H(+)- OH(-) junction with rectifying behaviour and H(+)-type and OH(-)-type complementary field effect transistors are demonstrated. We describe these devices with a model that relates H(+) and OH(-) to electron and hole transport in semiconductors. In turn, the model developed for these devices may provide additional insights into proton conduction in biological systems.

Electronic and optoelectronic materials and devices inspired by nature

Inorganic semiconductors permeate virtually every sphere of modern human existence. Micro-fabricated memory elements, processors, sensors, circuit elements, lasers, displays, detectors, etc are ubiquitous. However, the dawn of the 21st century has brought with it immense new challenges, and indeed opportunities-some of which require a paradigm shift in the way we think about resource use and disposal, which in turn directly impacts our ongoing relationship with inorganic semiconductors such as silicon and gallium arsenide. Furthermore, advances in fields such as nano-medicine and bioelectronics, and the impending revolution of the 'ubiquitous sensor network', all require new functional materials which are bio-compatible, cheap, have minimal embedded manufacturing energy plus extremely low power consumption, and are mechanically robust and flexible for integration with tissues, building structures, fabrics and all manner of hosts. In this short review article we summarize current progress in creating materials with such properties. We focus primarily on organic and bio-organic electronic and optoelectronic systems derived from or inspired by nature, and outline the complex charge transport and photo-physics which control their behaviour. We also introduce the concept of electrical devices based upon ion or proton flow ('ionics and protonics') and focus particularly on their role as a signal interface with biological systems. Finally, we highlight recent advances in creating working devices, some of which have bio-inspired architectures, and summarize the current issues, challenges and potential solutions. This is a rich new playground for the modern materials physicist.

A polysaccharide bioprotonic field-effect transistor

In nature, electrical signalling occurs with ions and protons, rather than electrons. Artificial devices that can control and monitor ionic and protonic currents are thus an ideal means for interfacing with biological systems. Here we report the first demonstration of a biopolymer protonic field-effect transistor with proton-transparent PdH(x) contacts. In maleic-chitosan nanofibres, the flow of protonic current is turned on or off by an electrostatic potential applied to a gate electrode. The protons move along the hydrated maleic-chitosan hydrogen-bond network with a mobility of ~4.9×10(-3) cm(2) V(-1) s(-1). This study introduces a new class of biocompatible solid-state devices, which can control and monitor the flow of protonic current. This represents a step towards bionanoprotonics.