Erik Josberger

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.

Proton conductivity in ampullae of Lorenzini jelly

Researchers find the proton conductivity of jelly found in the Ampullae of Lorenzini of sharks and skates to be unusually high. In 1678, Stefano Lorenzini first described a network of organs of unknown function in the torpedo ray—the ampullae of Lorenzini (AoL). An individual ampulla consists of a pore on the skin that is open to the environment, a canal containing a jelly and leading to an alveolus with a series of electrosensing cells. The role of the AoL remained a mystery for almost 300 years until research demonstrated that skates, sharks, and rays detect very weak electric fields produced by a potential prey. The AoL jelly likely contributes to this electrosensing function, yet the exact details of this contribution remain unclear. We measure the proton conductivity of the AoL jelly extracted from skates and sharks. The room-temperature proton conductivity of the AoL jelly is very high at 2 ± 1 mS/cm. This conductivity is only 40-fold lower than the current state-of-the-art proton-conducting polymer Nafion, and it is the highest reported for a biological material so far. We suggest that keratan sulfate, identified previously in the AoL jelly and confirmed here, may contribute to the high proton conductivity of the AoL jelly with its sulfate groups—acid groups and proton donors. We hope that the observed high proton conductivity of the AoL jelly may contribute to future studies of the AoL function.

An enzyme logic bioprotonic transducer

Translating ionic currents into measureable electronic signals is essential for the integration of bioelectronic devices with biological systems. We demonstrate the use of a Pd/PdHx electrode as a bioprotonic transducer that connects H+ currents in solution into an electronic signal. This transducer exploits the reversible formation of PdHx in solution according to PdH↔Pd + H+ + e−, and the dependence of this formation on solution pH and applied potential. We integrate the protonic transducer with glucose dehydrogenase as an enzymatic and gate for glucose and NAD+. PdHx formation and associated electronic current monitors the output drop in pH, thus transducing a biological function into a measurable electronic output.

Taking electrons out of bioelectronics: bioprotonic memories, transistors, and enzyme logic

The ability of bioelectronic devices to conduct protons and other ions opens up opportunities to interface with biology. In this research highlight, we report on our recent efforts in bioprotonic devices. These devices monitor and modulate a current of protons with an applied voltage. Voltage-controlled proton flow mimics semiconductor devices with complementary transistors or biological behaviors such as synaptic-like memories and enzyme logic.

Electronic control of H + current in a bioprotonic device with Gramicidin A and Alamethicin

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.

A Palladium-Binding Deltarhodopsin for Light-Activated Conversion of Protonic to Electronic Currents.

Fusion of a palladium-binding peptide to an archaeal rhodopsin promotes intimate integration of the lipid-embedded membrane protein with a palladium hydride protonic contact. Devices fabricated with the palladium-binding deltarhodopsin enable light-activated conversion of protonic currents to electronic currents with on/off responses complete in seconds and a nearly tenfold increase in electrical signal relative to those made with the wild-type protein.

Proton mediated control of biochemical reactions with bioelectronic pH modulation

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.

Electrical and electrochemical characterization of proton transfer at the interface between chitosan and PdHx

In bioelectronic medicine and electroceuticals, electronic devices that conduct electrons are used to monitor and control ion-based biochemical reactions in order to detect and treat medical conditions. Advancing these devices will require a thorough understanding of the electrochemical pathways that transduce electronic currents into the ionic currents that interact with the natural system. Here, we analyze the tranduction of electronic current into a protonic current (H+) using Pd/PdHx contacts and a model proton conductor, chitosan. Linear sweep voltammetry and electrochemical impedance spectroscopy data indicate that, for Pd, limited proton injection occurs at the interface aided by water oxidation. For PdHx, H desorption and electrochemical oxidation to H+ lead to sustainable proton injection and transfer to the chitosan protonic conductor. We have developed electroanalytical expressions and predictive digital simulations that match the experimental results. This work confirms that PdHx contacts integrated in DC devices, in parallel with electrochemical impedance spectroscopy, comprise a suitable means for measuring H+ currents and interrogating the proton conductivity in biomaterials.

Two-terminal proton conducting devices with synaptic behavior and memory

With the recent physical demonstration of memristive-based devices low-power two terminal devices with memory and learning functions have advanced electronics and neuromorphic computing. To this end, typically slow moving ions are coupled with fast moving electrons. Ionic motion affords memory, with electronic current as the output signal. Here, we introduce fully ionic two-terminal devices in which protons provide both memory and output signal. These devices exhibit synaptic-like reversible short-term depression, memory, and can be turned “ON” and “OFF” with as little as 30 fJ of energy per bit if appropriately miniaturized.