Enzymatically Polymerized Organic Conductors on Model Lipid Membranes.

Seamless integration between biological systems and electrical components is essential for enabling a twinned biochemical-electrical recording and therapy approach to understand and combat neurological disorders. Employing bioelectronic systems made up of conjugated polymers, which have an innate ability to transport both electronic and ionic charges, provides the possibility of such integration. In particular, translating enzymatically polymerized conductive wires, recently demonstrated in plants and simple organism systems, into mammalian models, is of particular interest for the development of next-generation devices that can monitor and modulate neural signals. As a first step toward achieving this goal, enzyme-mediated polymerization of two thiophene-based monomers is demonstrated on a synthetic lipid bilayer supported on a Au surface. Microgravimetric studies of conducting films polymerized in situ provide insights into their interactions with a lipid bilayer model that mimics the cell membrane. Moreover, the resulting electrical and viscoelastic properties of these self-organizing conducting polymers suggest their potential as materials to form the basis for novel approaches to in vivo neural therapeutics.

A Biologically Interfaced Evolvable Organic Pattern Classifier.

Future brain-computer interfaces will require local and highly individualized signal processing of fully integrated electronic circuits within the nervous system and other living tissue. New devices will need to be developed that can receive data from a sensor array, process these data into meaningful information, and translate that information into a format that can be interpreted by living systems. Here, the first example of interfacing a hardware-based pattern classifier with a biological nerve is reported. The classifier implements the Widrow-Hoff learning algorithm on an array of evolvable organic electrochemical transistors (EOECTs). The EOECTs' channel conductance is modulated in situ by electropolymerizing the semiconductor material within the channel, allowing for low voltage operation, high reproducibility, and an improvement in state retention by two orders of magnitude over state-of-the-art OECT devices. The organic classifier is interfaced with a biological nerve using an organic electrochemical spiking neuron to translate the classifier's output to a simulated action potential. The latter is then used to stimulate muscle contraction selectively based on the input pattern, thus paving the way for the development of adaptive neural interfaces for closed-loop therapeutic systems.

Metabolite-induced in vivo fabrication of substrate-free organic bioelectronics.

Interfacing electronics with neural tissue is crucial for understanding complex biological functions, but conventional bioelectronics consist of rigid electrodes fundamentally incompatible with living systems. The difference between static solid-state electronics and dynamic biological matter makes seamless integration of the two challenging. To address this incompatibility, we developed a method to dynamically create soft substrate-free conducting materials within the biological environment. We demonstrate in vivo electrode formation in zebrafish and leech models, using endogenous metabolites to trigger enzymatic polymerization of organic precursors within an injectable gel, thereby forming conducting polymer gels with long-range conductivity. This approach can be used to target specific biological substructures and is suitable for nerve stimulation, paving the way for fully integrated, in vivo-fabricated electronics within the nervous system.

Organic electrochemical neurons and synapses with ion mediated spiking.

Future brain-machine interfaces, prosthetics, and intelligent soft robotics will require integrating artificial neuromorphic devices with biological systems. Due to their poor biocompatibility, circuit complexity, low energy efficiency, and operating principles fundamentally different from the ion signal modulation of biology, traditional Silicon-based neuromorphic implementations have limited bio-integration potential. Here, we report the first organic electrochemical neurons (OECNs) with ion-modulated spiking, based on all-printed complementary organic electrochemical transistors. We demonstrate facile bio-integration of OECNs with Venus Flytrap (Dionaea muscipula) to induce lobe closure upon input stimuli. The OECNs can also be integrated with all-printed organic electrochemical synapses (OECSs), exhibiting short-term plasticity with paired-pulse facilitation and long-term plasticity with retention >1000 s, facilitating Hebbian learning. These soft and flexible OECNs operate below 0.6 V and respond to multiple stimuli, defining a new vista for localized artificial neuronal systems possible to integrate with bio-signaling systems of plants, invertebrates, and vertebrates.

Enzyme-assisted in vivo polymerisation of conjugated oligomer based conductors.

Conjugated polymers conduct both electronic and ionic carriers and thus can stimulate and translate biological signals when used as active materials in bioelectronic devices. Self- and on-demand organization of the active material directly in the in vivo environment can result in the seamless integration of the bioelectronic interface. Along that line, we recently demonstrated spontaneous in vivo polymerization of the conjugated oligomer ETE-S in the vascular tissue of plants and the formation of conducting wires. In this work, we elucidate the mechanism of the in vivo polymerization of the ETE-S trimer and demonstrate that ETE-S polymerizes due to an enzymatic reaction where the enzyme peroxidase is the catalyst and hydrogen peroxide is the oxidant. ETE-S, therefore, represents the first example of a conducting polymer that is enzymatically polymerized in vivo. By reproducing the reaction in vitro, we gain further insight on the polymerization mechanism and show that hydrogen peroxide is the limiting factor. In plants the ETE-S triggers the catalytic cycle responsible for the lignification process, hacks this biochemical pathway and integrates within the plant cell wall, forming conductors along the plant structure.

An Evolvable Organic Electrochemical Transistor for Neuromorphic Applications.

An evolvable organic electrochemical transistor (OECT), operating in the hybrid accumulation-depletion mode is reported, which exhibits short-term and long-term memory functionalities. The transistor channel, formed by an electropolymerized conducting polymer, can be formed, modulated, and obliterated in situ and under operation. Enduring changes in channel conductance, analogous to long-term potentiation and depression, are attained by electropolymerization and electrochemical overoxidation of the channel material, respectively. Transient changes in channel conductance, analogous to short-term potentiation and depression, are accomplished by inducing nonequilibrium doping states within the transistor channel. By manipulating the input signal, the strength of the transistor response to a given stimulus can be modulated within a range that spans several orders of magnitude, producing behavior that is directly comparable to short- and long-term neuroplasticity. The evolvable transistor is further incorporated into a simple circuit that mimics classical conditioning. It is forecasted that OECTs that can be physically and electronically modulated under operation will bring about a new paradigm of machine learning based on evolvable organic electronics.

Controlling the volatility of the written optical state in electrochromic DNA liquid crystals.

Liquid crystals are widely used in displays for portable electronic information display. To broaden their scope for other applications like smart windows and tags, new material properties such as polarizer-free operation and tunable memory of a written state become important. Here, we describe an anhydrous nanoDNA-surfactant thermotropic liquid crystal system, which exhibits distinctive electrically controlled optical absorption, and temperature-dependent memory. In the liquid crystal isotropic phase, electric field-induced colouration and bleaching have a switching time of seconds. Upon transition to the smectic liquid crystal phase, optical memory of the written state is observed for many hours without applied voltage. The reorientation of the DNA-surfactant lamellar layers plays an important role in preventing colour decay. Thereby, the volatility of optoelectronic state can be controlled simply by changing the phase of the material. This research may pave the way for developing a new generation of DNA-based, phase-modulated, photoelectronic devices.

High-Density Noncovalent Functionalization of DNA by Electrostatic Interactions.

Preserving DNA hybridization in organic solvents could someday serve to significantly extend the applicability of DNA-based technologies. Here, we present a method that can be used to solubilize double-stranded DNA at high concentrations in organic media. This method requires first precipitating a DNA molecule from the aqueous environment with an anilinium derivative and subsequently exchanging this moiety with an amine-containing surfactant in organic solvent. We demonstrate that this method yields complete exchange of the surfactant and allows for the modification of DNA with hydrophobic primary, secondary, and tertiary alkylamines and ordered functional π-systems. Using this approach, we fabricate a multichromophoric light harvesting system that would be unattainable by traditional methods. Additionally, this method makes it possible to use small, hydrophilic molecules to solubilize DNA in organic solvents, which reduces the shielding around the DNA and makes the macromolecule more accessible for further chemical modification. We believe that this approach will prove tremendously beneficial in expanding the scope of DNA-based nano- and biotechnologies.

Solvent-free liquid crystals and liquids based on genetically engineered supercharged polypeptides with high elasticity.

A series of solvent-free elastin-like polypeptide liquid crystals and liquids are developed by electrostatic complexation of supercharged elastin-like polypeptides with surfactants. The smectic mesophases exhibit a high elasticity and the values can be easily tuned by varying the alkyl chain lengths of the surfactants or the lengths of the elastin-like polypeptides.

Solvent-free Liquid Crystals and Liquids from DNA.

As DNA exhibits persistent structures with dimensions that exceed the range of their intermolecular forces, solid-state DNA undergoes thermal degradation at elevated temperatures. Therefore, the realization of solvent-free DNA fluids, including liquid crystals and liquids, still remains a significant challenge. To address this intriguing issue, we demonstrate that combining DNA with suitable cationic surfactants, followed by dehydration, can be a simple generic scheme for producing these solvent-free DNA fluid systems. In the anhydrous smectic liquid crystalline phase, DNA sublayers are intercalated between aliphatic hydrocarbon sublayers. The lengths of the DNA and surfactant are found to be extremely important in tuning the physical properties of the fluids. Stable liquid-crystalline and liquid phases are obtained in the -20 °C to 200 °C temperature range without thermal degradation of the DNA. Thus, a new type of DNA-based soft biomaterial has been achieved, which will promote the study and application of DNA in a much broader context.

Nucleic acid chemistry in the organic phase: from functionalized oligonucleotides to DNA side chain polymers.

DNA-incorporating hydrophobic moieties can be synthesized by either solid-phase or solution-phase coupling. On a solid support the DNA is protected, and hydrophobic units are usually attached employing phosphoramidite chemistry involving a DNA synthesizer. On the other hand, solution coupling in aqueous medium results in low yields due to the solvent incompatibility of DNA and hydrophobic compounds. Hence, the development of a general coupling method for producing amphiphilic DNA conjugates with high yield in solution remains a major challenge. Here, we report an organic-phase coupling strategy for nucleic acid modification and polymerization by introducing a hydrophobic DNA-surfactant complex as a reactive scaffold. A remarkable range of amphiphile-DNA structures (DNA-pyrene, DNA-triphenylphosphine, DNA-hydrocarbon, and DNA block copolymers) and a series of new brush-type DNA side-chain homopolymers with high DNA grafting density are produced efficiently. We believe that this method is an important breakthrough in developing a generalized approach to synthesizing functional DNA molecules for self-assembly and related technological applications.

Probing the shielding properties of aptameric protective groups.

Site-specific derivatization of chemically equivalent functional groups has recently been facilitated by the introduction of high-affinity aptamers as non-covalent protective groups. More specifically, a series of RNA aptamers have proven to be highly efficient in enhancing the regioselectivity of reactions with the aminoglycoside antibiotic neomycin B, which carries several chemically indistinguishable amino and hydroxy groups. Since small-molecule targets tend to exhibit multiple modes of binding with a single aptamer, the impact of secondary binding sites on the regioselectivity should be considered. To address this issue, we investigated a series of well-characterized RNA aptamers that bind neomycin B and propose a mechanism that accounts for the regioselective outcome of these transformations. We further demonstrate that the regioselectivity induced by non-covalent aptamer protective groups is determined by the number of binding sites, their affinity, and the mode of interaction with the guest molecule.

Conformationally constrained cyclic peptides: powerful scaffolds for asymmetric catalysis.

Cyclic peptides containing a disulfide bridge were identified as a simple and versatile coordination sphere for asymmetric catalysis. Upon complexation with Cu(2+) ions they catalyze Diels-Alder and Friedel-Crafts reactions with high enantioselectivities of up to 99% ee and 86% ee, respectively. Moreover, the peptides ligands were systematically optimized with the assistance of "Alanine Scanning". This biomolecular design could greatly expand the choice of peptide scaffolds for artificial metallopeptide catalysts.

Development of an electrochemical insulin sensor based on the insulin-linked polymorphic region.

Here we report the design and fabrication of an electrochemical aptamer-based (E-AB) sensor for detection of insulin. The aptamer used in this study is the insulin-linked polymorphic region (ILPR) sequence, a G-rich sequence that presumably undergoes ligand-induced folding to form a G-quadruplex in presence of insulin. Our circular dichroism data, however, suggests that the ILPR sequence, even in absence of the target, is predominantly in a G-quadruplex-like form. Insulin binding, however, has shown to further induce the formation of the G-quadruplex. To evaluate the potential of the ILPR sequence as a biosensing element, we constructed two E-AB insulin sensors that are identical in all aspects but the location of the methylene blue (MB) redox label. We find that the sensor fabricated with internal MB-modified probes (In-IT) shows enhanced sensing behavior when compared to one fabricated using terminal-MB modified probes (In1). The improvements observed with the In-IT sensor could be attributed to the more effective obstruction of electron transfer upon insulin binding. Overall, both sensors perform well, affording a detection limit of 10 nM and 50 nM for the In-IT and In1 sensors, respectively.

Design and characterization of an electrochemical peptide-based sensor fabricated via"click" chemistry.

We report an electrochemical peptide-based sensor fabricated via'click' chemistry for detection of anti-p24 antibodies. Our results also allude to a signaling mechanism similar to that of the linear probe electrochemical DNA sensor.

An electrochemical peptide-based biosensing platform for HIV detection.

We have fabricated a potentially generalizable electrochemical peptide-based (E-PB) sensor for the detection of HIV anti-p24 antibodies. The E-PB sensor is sensitive, specific and fares well even when challenged in a realistically complex medium such as human urine proxy.

Folding-based electrochemical DNA sensor fabricated on a gold-plated screen-printed carbon electrode.

Here we report a folding-based electrochemical DNA (E-DNA) sensor fabricated on a gold-plated screen-printed carbon electrode and show that the E-DNA sensor is not required to be fabricated on a relatively flat gold surface; the sensor works comparably well when fabricated on an electrodeposited gold film with a surface roughness factor of approximately 7.