Bioelectronics: A positive future for squid proteins

Superprotonic Conductivity in a Metalloporphyrin-Based SMOF (Supramolecular Metal-Organic Framework)

Metal-organic frameworks and supramolecular metal-organic frameworks (SMOFs) exhibit great potential for a broad range of applications taking advantage of the high surface area and pore sizes and tunable chemistry. In particular, metalloporphyrin-based MOFs and SMOFs are becoming of great importance in many fields due to the bioessential functions of these macrocycles that are being mimicked. On the other hand, during the last years, proton-conducting materials have aroused much interest, and those presenting high conductivity values are potential candidates to play a key role in some solid-state electrochemical devices such as batteries and fuel cells. In this way, using metalloporphyrins as building units we have obtained a new crystalline material with formula [H(bipy)]2[(MnTPPS)(H2O)2]·2bipy·14H2O, where bipy is 4,4'-bipyidine and TPPS4- is the meso-tetra(4-sulfonatephenyl) porphyrin. The crystal structure shows a zig-zag water chain along the [100] direction located between the sulfonate groups of the porphyrin. Taking into account those structural features, the compound was tested for proton conduction by complex electrochemical impedance spectroscopy (EIS). The as-obtained conductivity is 1 × 10-2 S·cm-1 at 40 °C and 98% relative humidity, which is a remarkably high value.

Electronic control of H+ current in a bioprotonic device with carbon nanotube porins

Hybrid biotic abiotic devices can be used to interface electronics with biological systems for novel therapies or to increase device functionality beyond silicon. Many strategies exist to merge the electronic and biological worlds, one dominated by electrons and holes as charge carriers, the other by ions. In the biological world, lipid bilayers and ion channels are essential to compartmentalize the cell machinery and regulate ionic fluxes across the cell membrane. Here, we demonstrate a bioelectronic device in which a lipid bilayer supported on H+-conducting Pd/PdHx contacts contains carbon nanotubes porin (CNTP) channels. This bioelectronic device uses CNTPs to control of H+ flow across the lipid bilayer with a voltage applied to the Pd/PdHx contacts. Potential applications of these devices include local pH sensing and control.

A protonic biotransducer controlling mitochondrial ATP synthesis

In nature, protons (H⁺) play an important role in biological activities such as in mitochondrial ATP synthesis, which is driven by a H⁺ gradient across the inner membrane, or in the activation of acid sensing ion channels in neuron cells. Bioprotonic devices directly interface with the H⁺ concentration (pH) to facilitate engineered interactions with these biochemical processes. Here we develop a H⁺ biotransducer that changes the pH in a mitochondrial matrix by controlling the flow of H⁺ between a conductive polymer of sulfonated polyaniline and solution. We have successfully modulated the rate of ATP synthesis in mitochondria by altering the solution pH. Our H⁺ biotransducer provides a new way to monitor and modulate pH dependent biological functions at the interface between the electronic devices and biological materials.

Taking Electrons out of Bioelectronics: From Bioprotonic Transistors to Ion Channels

From cell-to-cell communication to metabolic reactions, ions and protons (H+) play a central role in many biological processes. Examples of H+ in action include oxidative phosphorylation, acid sensitive ion channels, and pH dependent enzymatic reactions. To monitor and control biological reactions in biology and medicine, it is desirable to have electronic devices with ionic and protonic currents. Here, we summarize our latest efforts on bioprotonic devices that monitor and control a current of H+ in physiological conditions, and discuss future potential applications. Specifically, we describe the integration of these devices with enzymatic logic gates, bioluminescent reactions, and ion channels.

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.

Protein-Based Bioelectronics

The desire for flexible electronics is booming, and development of bioelectronics for health monitoring, internal body procedures, and other biomedical applications is heavily responsible for the growing market. Most current fabrication techniques for flexible bioelectronics, however, do not use materials that optimize both biocompatibility and mechanical properties. This Review explores flexible electronic technologies, fabrication methods, and protein materials for biomedical applications. With favorable sustainability and biocompatibility, naturally derived proteins are an exceptional alternative to synthetic materials currently used. Many proteins can take on various forms, such as fibers, films, and scaffolds. The fabrication of resistors and organic solar cells on silk has already been proven, and optoelectronics made of collagen and keratin have also been explored. The flexibility and biocompatibility of these materials along with their proven performance in electronics make them ideal materials in the advancement of biomedical devices.

Proton conductivity in ampullae of Lorenzini jelly

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.

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.

3D proton transfer augments bio-photocurrent generation

An enhancement of the photocurrent is achieved in a biohybrid nanocomposite consisting of nanovesicle reconstituted proteorhodopsin and potassium phosphotungstate nanoparticles. With the observation of an accelerated protein photocycle and elevated proton conductivity, this improvement of the photo-electric performance is attributed to the construction of a 3D proton-transfer framework.