A Memristive Element Based on an Electrically Controlled Single-Molecule Reaction

A single-molecule memory element is electrically-controlled using two distinct reaction mechanisms as reported by K. Moth-Poulsen, J. Hihath, and co-workers (DOI:10.1002/anie.202002300). By using separate electrically-controllable reactions for the forward and reverse reactions the bistable norbornadiene-quadricyclane system can be set in either state. The device can be switched through multiple cycles when a square-wave voltage signal is applied to the molecule. Each state has a unique conductance value allowing the system to act as a switch or memory device

Thermal and electrochemical gate effects on DNA conductance

Abstract In an attempt to understand the complexities of DNA charge transport we have used a scanning tunnelling microscope break junction to repeatedly form a large number of Au-DNA-Au junctions. The DNA is covalently bound to the Au electrodes via gold-thiol bonds, and all measurements are carried out in an aqueous buffer solution to maintain a biological conformation of the duplex. A statistical analysis is carried out to determine the conductance of a single DNA duplex. Previously, we have seen an algebraic dependence of the conductance on length, suggesting a hopping mechanism. To attempt to verify this as the conduction mechanism we have changed the solution temperature and applied an electrochemical gate to the molecular junction to help elucidate the charge transport properties. In an alternating GC sequence with a length of eight base pairs, neither the temperature nor the gate potential caused a significant change in the conductance within the available experimental window

A Chirality-Based Quantum Leap

There is increasing interest in the study of chiral degrees of freedom occurring in matter and in electromagnetic fields. Opportunities in quantum sciences will likely exploit two main areas that are the focus of this Review: (1) recent observations of the chiral-induced spin selectivity (CISS) effect in chiral molecules and engineered nanomaterials and (2) rapidly evolving nanophotonic strategies designed to amplify chiral light-matter interactions. On the one hand, the CISS effect underpins the observation that charge transport through nanoscopic chiral structures favors a particular electronic spin orientation, resulting in large room-temperature spin polarizations. Observations of the CISS effect suggest opportunities for spin control and for the design and fabrication of room-temperature quantum devices from the bottom up, with atomic-scale precision and molecular modularity. On the other hand, chiral-optical effects that depend on both spin- and orbital-angular momentum of photons could offer key advantages in all-optical and quantum information technologies. In particular, amplification of these chiral light-matter interactions using rationally designed plasmonic and dielectric nanomaterials provide approaches to manipulate light intensity, polarization, and phase in confined nanoscale geometries. Any technology that relies on optimal charge transport, or optical control and readout, including quantum devices for logic, sensing, and storage, may benefit from chiral quantum properties. These properties can be theoretically and experimentally investigated from a quantum information perspective, which has not yet been fully developed. There are uncharted implications for the quantum sciences once chiral couplings can be engineered to control the storage, transduction, and manipulation of quantum information. This forward-looking Review provides a survey of the experimental and theoretical fundamentals of chiral-influenced quantum effects and presents a vision for their possible future roles in enabling room-temperature quantum technologies.ISSN:1936-0851ISSN:1936-086

A machine learning approach for accurate and real-time DNA sequence identification

BackgroundThe all-electronic Single Molecule Break Junction (SMBJ) method is an emerging alternative to traditional polymerase chain reaction (PCR) techniques for genetic sequencing and identification. Existing work indicates that the current spectra recorded from SMBJ experimentations contain unique signatures to identify known sequences from a dataset. However, the spectra are typically extremely noisy due to the stochastic and complex interactions between the substrate, sample, environment, and the measuring system, necessitating hundreds or thousands of experimentations to obtain reliable and accurate results.ResultsThis article presents a DNA sequence identification system based on the current spectra of ten short strand sequences, including a pair that differs by a single mismatch. By employing a gradient boosted tree classifier model trained on conductance histograms, we demonstrate that extremely high accuracy, ranging from approximately 96 % for molecules differing by a single mismatch to 99.5 % otherwise, is possible. Further, such accuracy metrics are achievable in near real-time with just twenty or thirty SMBJ measurements instead of hundreds or thousands. We also demonstrate that a tandem classifier architecture, where the first stage is a multiclass classifier and the second stage is a binary classifier, can be employed to boost the single mismatched pair's identification accuracy to 99.5 %.ConclusionsA monolithic classifier, or more generally, a multistage classifier with model specific parameters that depend on experimental current spectra can be used to successfully identify DNA strands

Conformational gating of DNA conductance.

DNA is a promising molecule for applications in molecular electronics because of its unique electronic and self-assembly properties. Here we report that the conductance of DNA duplexes increases by approximately one order of magnitude when its conformation is changed from the B-form to the A-form. This large conductance increase is fully reversible, and by controlling the chemical environment, the conductance can be repeatedly switched between the two values. The conductance of the two conformations displays weak length dependencies, as is expected for guanine-rich sequences, and can be fit with a coherence-corrected hopping model. These results are supported by ab initio electronic structure calculations that indicate that the highest occupied molecular orbital is more disperse in the A-form DNA case. These results demonstrate that DNA can behave as a promising molecular switch for molecular electronics applications and also provide additional insights into the huge dispersion of DNA conductance values found in the literature

Mapping DNA Conformations Using Single-Molecule Conductance Measurements

DNA is an attractive material for a range of applications in nanoscience and nanotechnology, and it has recently been demonstrated that the electronic properties of DNA are uniquely sensitive to its sequence and structure, opening new opportunities for the development of electronic DNA biosensors. In this report, we examine the origin of multiple conductance peaks that can occur during single-molecule break-junction (SMBJ)-based conductance measurements on DNA. We demonstrate that these peaks originate from the presence of multiple DNA conformations within the solutions, in particular, double-stranded B-form DNA (dsDNA) and G-quadruplex structures. Using a combination of circular dichroism (CD) spectroscopy, computational approaches, sequence and environmental controls, and single-molecule conductance measurements, we disentangle the conductance information and demonstrate that specific conductance values come from specific conformations of the DNA and that the occurrence of these peaks can be controlled by controlling the local environment. In addition, we demonstrate that conductance measurements are uniquely sensitive to identifying these conformations in solutions and that multiple configurations can be detected in solutions over an extremely large concentration range, opening new possibilities for examining low-probability DNA conformations in solutions

A Memristive Element Based on an Electrically Controlled Single‐Molecule Reaction

A single-molecule memory element is electrically-controlled using two distinct reaction mechanisms as reported by K. Moth-Poulsen, J. Hihath, and co-workers (DOI:10.1002/anie.202002300). By using separate electrically-controllable reactions for the forward and reverse reactions the bistable norbornadiene-quadricyclane system can be set in either state. The device can be switched through multiple cycles when a square-wave voltage signal is applied to the molecule. Each state has a unique conductance value allowing the system to act as a switch or memory device

Self-Aligning Nanojunctions for Integrated Single-Molecule Circuits

Robust, high-yield integration of nanoscale materials such as graphene nanoribbons, nanoparticles, or single-molecules with conventional electronic circuits has proven to be challenging. This difficulty arises because the contacts to these nanomaterials must be precisely fabricated with angstrom-level resolution to make reliable connections, and at manufacturing scales this cannot be achieved with even the highest-resolution lithographic tools. Here we introduce an approach that circumvents this issue by precisely synthesizing nanometer-scale gaps between metallic electrodes using a self-aligning, solution-phase process, which allows facile integration with conventional electronic systems with yields approaching 50%. The electrode separation is controlled by covalently binding metallic single-walled carbon nanotube (mCNT) electrodes to individual DNA duplexes to synthesize hybrid mCNT-DNA-mCNT nanojunctions, where the gap is precisely matched to the DNA length. Upon integration, the resulting single-molecule circuits have electronic properties dominated by the DNA in the junction, have reproducible conductance values with low dispersion, and are stable and robust enough to be utilized as active, high-specificity electronic biosensors for dynamic single-molecule detection of specific oligonucleotides, such as those related to the SARS-CoV-2 genome. This scalable approach for high-yield integration of nanometer-scale materials will create new opportunities for manufacturing hybrid electronic systems for a wide range of applications