Synthesis of pyridine chitosan and its protonic conductivity

Constructing Two-Dimensional (2D) Heterostructure Channels with Engineered Biomembrane and Graphene for Precise Scandium Sieving

The special properties of rare earth elements (REE) have effectively broadened their application fields. How to accurately recognize and efficiently separate target rare earth ions with similar radii and chemical properties remains a formidable challenge. Here, precise two-dimensional (2D) heterogeneous channels are constructed using engineered E. coli membranes between graphene oxide (GO) layers. The difference in binding ability and corresponding conformational change between Lanmodulin (LanM) and rare earth ions in the heterogeneous channel allows for precisely recognizing and sieving of scandium ions (Sc3+). The engineered E. coli membranes not only can protect the integrity of structure and functionality of LanM, the rich lipids and sugars, but also help the Escherichia coli (E. coli) membranes closely tile on the GO nanosheets through interaction, preventing swelling and controlling interlayer spacing accurately down to the sub-nanometer. Apparently, the 2D heterogeneous channels showcase excellent selectivity for trivalent ions (SFFe /Sc≈3), especially for Sc3+ ions in REE with high selectivity (SFCe/Sc≈167, SFLa/Sc≈103). The long-term stability and tensile strain tests verify the membrane's outstanding stability. Thus, this simple, efficient, and cost-effective work provides a suggestion for constructing 2D interlayer heterogeneous channels for precise sieving, and this valuable strategy is proposed for the efficient extraction of Sc.

Solid-State Molecular Protonics Devices of Solid-Supported Biological Membranes Reveal the Mechanism of Long-Range Lateral Proton Transport

Lateral proton transport (PT) on the surface of biological membranes is a fundamental biochemical process in the bioenergetics of living cells, but a lack of available experimental techniques has resulted in a limited understanding of its mechanism. Here, we present a molecular protonics experimental approach to investigate lateral PT across membranes by measuring long-range (70 μm) lateral proton conduction via a few layers of lipid bilayers in a solid-state-like environment, i.e., without having bulk water surrounding the membrane. This configuration enables us to focus on lateral proton conduction across the surface of the membrane while decoupling it from bulk water. Hence, by controlling the relative humidity of the environment, we can directly explore the role of water in the lateral PT process. We show that proton conduction is dependent on the number of water molecules and their structure and on membrane composition, where we explore the role of the headgroup, the tail saturation, the membrane phase, and membrane fluidity. The measured PT as a function of temperature shows an inverse temperature dependency, which we explain by the desorption and adsorption of water molecules into the solid membrane platform. We explain our findings by discussing the role of percolating hydrogen bonding within the membrane structure in a Grotthuss-like mechanism.

Glycoproteins as a Platform for Making Proton-Conductive Free-Standing Biopolymers

Biopolymers are an attractive environmentally friendly alternative to common synthetic polymers, whereas primarily proteins and polysaccharides are the biomacromolecules that are used for making the biopolymer. Due to the breadth of side chains of such biomacromolecules capable of participating in hydrogen bonding, proteins and polysaccharide biopolymers were also used for the making of proton-conductive biopolymers. Here, we introduce a new platform for combining the merits of both proteins and polysaccharides while using a glycosylated protein for making the biopolymer. We use mucin as our starting point, whereas being a waste of the food industry, it is a highly available and low-cost glycoprotein. We show how we can use different chemical strategies to target either the glycan part or specific amino acids for both crosslinking between the different glycoproteins, thus making a free-standing biopolymer, as well as for introducing superior proton conductivity properties to the formed biopolymer. The resultant proton-conductive soft biopolymer is an appealing candidate for any soft bioelectronic application.

Resistance-Based Lateral Flow Immunosensor with a NFC-Enabled Smartphone for Rapid Diagnosis of Leptospirosis in Clinical Samples

Leptospirosis is one of the most life-threatening tropical diseases caused by pathogenic Leptospira. To date, a diagnostic device that offers rapid and sensitive detection of leptospires has been still in demand for proper treatment to reduce the mortality rate. Herein, we create a resistance-based lateral flow immunosensor diagnosis device (R-LFI) that integrates near-field communication (NFC) with a portable smartphone for leptospiral detection in clinical samples. A specific monoclonal antibody against the pathogen was coated on a nitrocellulose membrane (NCM) where the test line was collocated. Two electrodes with a sandwich-like configuration were installed employing a conductive double-sided adhesive tape and connected with a NFC smartphone-based detection system. A half-sandwich immunocomplex formation induced high proton conduction, resulting in a considerable decrement in resistive response. The performance of the R-LFI sensor was evaluated using recombinant LipL32 (rLipL32), Leptospira interrogans, and clinical samples. The R-LFI device exhibited linear responses toward rLipL32 protein in phosphate buffer and L. interrogans-spiked healthy human serum samples within the concentration ranging from 1 to 1000 ng mL^-1 (limit of detection (LOD): 0.29 ng mL^-1) and from 10⁴ to 10⁶ cell mL^-1 (LOD: 4.89 × 10³ cell mL^-1), respectively. Our R-LFI sensor successfully detected L. interrogans-positive clinical samples as confirmed by polymerase chain reaction (PCR). This platform offers high specificity, selectivity, simplicity, miniscule sample volume, and no labeling element requirement. These desirable features make it particularly suitable for countries where medical facilities and resources are limited.

Natural biopolymers as proton conductors in bioelectronics

Bioelectronic devices sense or deliver information at the interface between living systems and electronics by converting biological signals into electronic signals and vice-versa. Biological signals are typically carried by ions and small molecules. As such, ion conducting materials are ideal candidates in bioelectronics for an optimal interface. Among these materials, ion conducting polymers that are able to uptake water are particularly interesting because, in addition to ionic conductivity, their mechanical properties can closely match the ones of living tissue. In this review, we focus on a specific subset of ion-conducting polymers: proton (H⁺ ) conductors that are naturally derived. We first provide a brief introduction of the proton conduction mechanism, and then outline the chemical structure and properties of representative proton-conducting natural biopolymers: polysaccharides (chitosan and glycosaminoglycans), peptides and proteins, and melanin. We then highlight examples of using these biopolymers in bioelectronic devices. We conclude with current challenges and future prospects for broader use of natural biopolymers as proton conductors in bioelectronics and potential translational applications.

Enhanced Proton Conductivity across Protein Biopolymers Mediated by Doped Carbon Nanoparticles

Carbon nanoparticles, known as carbon-dots (C-Dots), are famous for their optoelectronic properties. Here it is shown that C-Dots can also mediate protons, where protein biopolymers are used as the protonic transport matrix. Energy transfer measurements indicate that different doped C-Dots bind to the protein biopolymer in different efficiencies. Electrical impedance measurements reveal enhanced conductance across the protein biopolymer upon C-Dots integration, dependent on the doping type. The enhanced conductivity is attributed to protonic conduction due to the large observed kinetic isotope effect, resulting in one of the highest measured proton conductivity across protein biopolymers. Transistor measurements show that the various doped C-Dots-protein biopolymer exhibit different increase in charge carrier density and in carrier mobility, suggesting different modes of proton transport. The ability of C-Dots to support protonic conduction opens a field of carbon-based protonic nanoparticles and due to the formation simplicity of C-Dots they can be integrated in a variety of protonic devices.

Biocompatible and Biodegradable Functional Polysaccharides for Flexible Humidity Sensors

Using wearable devices to monitor respiration rate is essential for reducing the risk of death or permanent injury in patients. Improving the performance and safety of these devices and reducing their environmental footprint could advance the currently used health monitoring technologies. Here, we report high-performance, flexible bioprotonic devices made entirely of biodegradable biomaterials. This smart sensor satisfies all the requirements for monitoring human breathing states, including noncontact characteristic and the ability to discriminate humidity stimuli with ultrahigh sensitivity, rapid response time, and excellent cycling stability. In addition, the device can completely decompose after its service life, which reduces the risk to the human body. The cytotoxicity test demonstrates that the device shows good biocompatibility based on the viability of human skin fibroblast-HSAS1 cells and human umbilical vein endothelial (HUVECs), illustrating the safety of the sensor upon integration with the human skin.

Proton conductivity of glycosaminoglycans

Proton conductivity is important in many natural phenomena including oxidative phosphorylation in mitochondria and archaea, uncoupling membrane potentials by the antibiotic Gramicidin, and proton actuated bioluminescence in dinoflagellate. In all of these phenomena, the conduction of protons occurs along chains of hydrogen bonds between water and hydrophilic residues. These chains of hydrogen bonds are also present in many hydrated biopolymers and macromolecule including collagen, keratin, chitosan, and various proteins such as reflectin. All of these materials are also proton conductors. Recently, our group has discovered that the jelly found in the Ampullae of Lorenzini- shark’s electro-sensing organs- is the highest naturally occurring proton conducting substance. The jelly has a complex composition, but we proposed that the conductivity is due to the glycosaminoglycan keratan sulfate (KS). Here we measure the proton conductivity of hydrated keratan sulfate purified from Bovine Cornea. PdH_x contacts at 0.50 ± 0.11 mS cm ^-1, which is consistent to that of Ampullae of Lorenzini jelly at 2 ± 1 mS cm ^-1. Proton conductivity, albeit with lower values, is also shared by other glycosaminoglycans with similar chemical structures including dermatan sulfate, chondroitin sulfate A, heparan sulfate, and hyaluronic acid. This observation supports the relationship between proton conductivity and the chemical structure of biopolymers.

Macroscale Biomolecular Electronics and Ionics

The conduction of ions and electrons over multiple length scales is central to the processes that drive the biological world. The multidisciplinary attempts to elucidate the physics and chemistry of electron, proton, and ion transfer in biological charge transfer have focused primarily on the nano- and microscales. However, recently significant progress has been made on biomolecular materials that can support ion and electron currents over millimeters if not centimeters. Likewise, similar transport phenomena in organic semiconductors and ionics have led to new innovations in a wide variety of applications from energy generation and storage to displays and bioelectronics. Here, the underlying principles of conduction on the macroscale in biomolecular materials are discussed, highlighting recent examples, and particularly the establishment of accurate structure-property relationships to guide rationale material and device design. The technological viability of biomolecular electronics and ionics is also discussed.

Hydrogen bonding, π-π stacking and van der Waals forces-dominated layered regions in the crystal structure of 4-amino-pyridinium hydrogen (9-phosphono-non-yl)phospho-nate

The asymmetric unit of the title mol-ecular salt, [C5H7N2+][(HO)2OP(CH2)9PO2(OH)-], consists of one 4-amino-pyridinium cation and one hydrogen (9-phos-phono-non-yl)phospho-nate anion, both in general positions. As expected, the 4-amino-pyridinium moieties are protonated exclusively at their endocyclic nitro-gen atom due to a mesomeric stabilization by the imine form which would not be given in the corresponding double-protonated dicationic species. In the crystal, the phosphonyl (-PO3H2) and hydrogen phospho-nate (-PO3H) groups of the anions form two-dimensional O-H⋯O hydrogen-bonded networks in the ab plane built from 24-membered hydrogen-bonded ring motifs with the graph-set descriptor R66(24). These networks are pairwise linked by the anions' alkyl-ene chains. The 4-amino-pyridinium cations are stacked in parallel displaced face-to-face arrangements and connect neighboring anionic substructures via medium-strong charge-supported N-H⋯O hydrogen bonds along the c axis. The resulting three-dimensional hydrogen-bonded network shows clearly separated hydro-philic and hydro-phobic structural domains.

Long-Range Proton Conduction across Free-Standing Serum Albumin Mats

Free-standing serum-albumin mats can transport protons over millimetre length-scales. The results of photoinduced proton transfer and voltage-driven proton-conductivity measurements, together with temperature-dependent and isotope-effect studies, suggest that oxo-amino-acids of the protein serum albumin play a major role in the translocation of protons via an "over-the-barrier" hopping mechanism. The use of proton-conducting protein mats opens new possibilities for bioelectronic interfaces.