Stability of DNA Origami Nanostructure under Diverse Chemical Environments

We report the effect of chemical and physical treatments on the structural stability of DNA origami nanostructures. Our result shows that DNA nanostructure maintains its shape under harsh processing conditions, including thermal annealing up to 200 °C for 10 min, immersing in a wide range of organic solvents for up to 24 h, brief exposure to alkaline aqueous solutions, and 5 min exposure to UV/O₃. Our result suggests that the application window of DNA nanostructure is significantly wider than previously believed

Interaction of Magnesium Ions with Pristine Single-Layer and Defected Graphene/Water Interfaces Studied by Second Harmonic Generation

This work reports thermodynamic and electrostatic parameters for fused silica/water interfaces containing cm²-sized graphene ranging from a single layer of pristine graphene to defected graphene. Second harmonic generation (SHG) measurements carried out at pH 7 indicate that the surface charge density of the fused silica/water interface containing the defected graphene (−0.009(3) to −0.010(3) C/m²) is between that of defect-free single layer graphene (−0.0049(8) C/m²) and bare fused silica (−0.013(6) C/m²). The interfacial free energy of the fused silica/water interface calculated from the Lippmann equation is reduced by a factor of 7 in the presence of single-layer pristine graphene, while defected graphene reduces it only by a factor of at most 2. Subsequent SHG adsorption isotherm studies probing the Mg²⁺ adsorption at the fused silica/water interface result in fully reversible metal ion interactions and observed binding constants, <i>K</i>_ads, of 4(1) – 5(1) × 10³ M^–1 for pristine graphene and 3(1) – 4(1) × 10³ M^–1 for defected graphene, corresponding to adsorption free energies, Δ<i>G</i>_ads, referenced to the 55.5 molarity of water, of −30(1) to −31.1(7) kJ/mol for both interfaces, comparable to Mg²⁺ adsorption at the bare fused silica/water interface. Maximum Mg²⁺ ion densities are obtained from Gouy–Chapman model fits to the Langmuir adsorption isotherms and found to range from 1.1(5) – 1.5(4) × 10¹² ions adsorbed per cm² for pristine graphene and 2(1) – 3.1(5) × 10¹² ions adsorbed per cm² for defected graphene, slightly smaller than those of for Mg²⁺ adsorption at the bare fused silica/water interface ((2–4) × 10¹² ions adsorbed per cm²), assuming the magnesium ions are bound as divalent species. We conclude that the presence of defects in the graphene sheet, which we estimate here to be around 1.3 × 10¹¹ cm², imparts only subtle changes in the thermodynamic and electrostatic parameters quantified here

Graphene Nucleation Density on Copper: Fundamental Role of Background Pressure

<p>In this paper we discuss the effect of background pressure and synthesis temperature on the graphene crystal sizes in chemical vapor deposition (CVD) on copper catalyst. For the first time, we quantitatively demonstrate a fundamental role of the background pressure and provide the activation energy for graphene nucleation in atmospheric pressure CVD (9 eV), which is substantially higher than for low pressure CVD (4 eV). We attribute the difference to a greater importance of copper sublimation in low pressure CVD, where severe copper evaporation likely dictates the desorption rate of active carbon from the surface. At atmospheric pressure, where copper evaporation is suppressed, the activation energy is assigned to the desorption energy of carbon clusters instead. The highest possible temperature, close to the melting point of copper, should be used for large single crystal graphene synthesis. Using these conditions, we have synthesized graphene single crystals approaching 1 mm in size. Single crystal nature of synthesized graphene was confirmed by low energy electron diffraction. We also demonstrate that CVD of graphene at temperatures below 1000 oC shows higher nucleation density on (111) than on (100) and (101) copper surfaces but there is no identifiable preference at higher temperatures.</p