Self-Aligning Nanojunctions for Integrated Single-Molecule Circuits.

Robust, high-yield integration of nanoscale components 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 nanoscale devices 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 creating nanometer-scale gaps between metallic carbon electrodes by 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 create mCNT-DNA-mCNT nanojunctions, where the gap is precisely matched to the DNA length. These junctions are then integrated with top-down lithographic techniques to create single-molecule circuits that 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 devices will enable opportunities for manufacturing of hybrid electronic systems for a wide range of applications.

Structure-Dependent Electrical Conductance of DNA Origami Nanowires.

Exploring the structural and electrical properties of DNA origami nanowires is an important endeavor for the advancement of DNA nanotechnology and DNA nanoelectronics. Highly conductive DNA origami nanowires are a desirable target for creating low-cost self-assembled nanoelectronic devices and circuits. In this work, the structure-dependent electrical conductance of DNA origami nanowires is investigated. A silicon nitride (Si3 N4 ) on silicon semiconductor chip with gold electrodes was used for collecting electrical conductance measurements of DNA origami nanowires, which are found to be an order of magnitude less electrically resistive on Si3 N4 substrates treated with a monolayer of hexamethyldisilazane (HMDS) (∼1013 ohms) than on native Si3 N4 substrates without HMDS (∼1014 ohms). Atomic force microscopy (AFM) measurements of the height of DNA origami nanowires on mica and Si3 N4 substrates reveal that DNA origami nanowires are ∼1.6 nm taller on HMDS-treated substrates than on the untreated ones indicating that the DNA origami nanowires undergo increased structural deformation when deposited onto untreated substrates, causing a decrease in electrical conductivity. This study highlights the importance of understanding and controlling the interface conditions that affect the structure of DNA and thereby affect the electrical conductance of DNA origami nanowires.

Gold Nanoparticle Synthesis.

Gold nanoparticles (Au nanoparticles) that are ~12 nm in diameter were synthesized by rapidly injecting a solution of 150 mg (0.15 mmol) of tetrachloroauric acid in 3.0 g (3.7 mmol, 3.6 mL) of oleylamine (technical grade) and 3.0 mL of toluene into a boiling solution of 5.1 g (6.4 mmol, 8.7 mL) of oleylamine in 147 mL of toluene. While boiling and mixing the reaction solution for 2 hours, the color of the reaction mixture changed from clear, to light yellow, to light pink, and then slowly to dark red. The heat was then turned off, and the solution was allowed to gradually cool down to room temperature for 1 hour. The gold nanoparticles were then collected and separated from the solution using a centrifuge and washed three times; by vortexing and dispersing the gold nanoparticles in 10 mL portions of toluene, and then precipitating the gold nanoparticles by adding 40 mL portions of methanol and spinning them in a centrifuge. The solution was then decanted to remove any remaining byproducts and unreacted starting materials. Drying the gold nanoparticles in a vacuum environment produced a solid black pellet; which could be stored for long periods of time (up to one year) for later use, and then redissolved in organic solvents such as toluene.