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The ultrafast monitoring of deoxyribonucleic acid (DNA) dynamic structural changes is an emerging and rapidly growing research topic in biotechnology. The existing optical spectroscopy used to identify different dynamical DNA structures lacks quick response while requiring large consumption of samples and bulky instrumental facilities. It is highly demanded to develop an ultrafast technique that monitors DNA structural changes with the external stimulus or cancer‐related disease scenarios. Here, we demonstrate a novel photonic integrated graphene‐optofluidic device to monitor DNA structural changes with the ultrafast response time. Our approach is featured with an effective and straightforward design of decoding the electronic structure change of graphene induced by its interactions with DNAs in different conformations using ultrafast nanosecond pulse laser and achieving refractive index sensitivity of ~3 × 10−5 RIU. This innovative technique for the first time allows us to perform ultrafast monitoring of the conformational changes of special DNA molecules structures, including G‐quadruplex formation by K+ ions and i‐motif formation by the low pH stimulus. The graphene‐optofluidic device as presented here provides a new class of label‐free, ultrafast, ultrasensitive, compact, and cost‐effective optical biosensors for medical and healthcare applications.

Quantum dots (QD) with electric-field-controlled charge state are promising for electronics applications, e.g., digital information storage, single-electron transistors, and quantum computing. Inor...

The kagome lattice, whose electronic valence band (VB) structure includes two Dirac bands and one flat band, offers a rich space to realise tuneable topological and strongly correlated electronic phases in two-dimensional (2D) and layered materials. While strong electron correlations have been observed in inorganic kagome crystals, they remain elusive in organic systems. The latter offer versatile synthesis protocols via molecular self-assembly and metal-ligand coordination. Here, we report the synthesis of a 2D metal-organic framework (MOF) where di-cyano-anthracene (DCA) molecules form a kagome arrangement via coordination with copper (Cu) atoms on a silver surface [Ag(111)]. Low-temperature scanning tunnelling spectroscopy revealed Kondo screening--by the Ag(111) conduction electrons--of magnetic moments localised at Cu and DCA sites of the MOF. Density functional theory and mean-field Hubbard modelling show that these local moments emerge from strong interactions between kagome MOF electrons, enabling organic 2D materials as viable platforms for strongly correlated nanoelectronics and spintronics., Main text: 32 pages, 5 figures. Supplementary Information: 51 pages, 20 figures

We use angle-resolved photoemission spectroscopy to investigate the electronic structure of bilayer graphene at high n-doping and extreme displacement fields, created by intercalating epitaxial monolayer graphene on silicon carbide with magnesium to form quasi-freestanding bilayer graphene on magnesium-terminated silicon carbide. Angle-resolved photoemission spectroscopy reveals that upon magnesium intercalation, the single massless Dirac band of epitaxial monolayer graphene is transformed into the characteristic massive double-band Dirac spectrum of quasi-freestanding bilayer graphene. Analysis of the spectrum using a simple tight binding model indicates that magnesium intercalation results in an n-type doping of 2.1 $\times$ 10$^{14}$ cm$^{-2}$, creates an extremely high displacement field of 2.6 V/nm, opening a considerable gap of 0.36 eV at the Dirac point. This is further confirmed by density-functional theory calculations for quasi-freestanding bilayer graphene on magnesium-terminated silicon carbide, which show a similar doping level, displacement field and bandgap. Finally, magnesium-intercalated samples are surprisingly robust to ambient conditions; no significant changes in the electronic structure are observed after 30 minutes exposure in air., 46 pages including supporting information, 4 figures in the main paper and 9 figures in the supporting information

Supramolecular chemistry protocols applied on surfaces offer compelling avenues for atomic-scale control over organic-inorganic interface structures. In this approach, adsorbate-surface interactions and two-dimensional confinement can lead to morphologies and properties that differ dramatically from those achieved via conventional synthetic approaches. Here, we describe the bottom-up, on-surface synthesis of one-dimensional coordination nanostructures based on an iron (Fe)-terpyridine (tpy) interaction borrowed from functional metal-organic complexes used in photovoltaic and catalytic applications. Thermally activated diffusion of sequentially deposited ligands and metal atoms and intraligand conformational changes lead to Fe-tpy coordination and formation of these nanochains. We used low-temperature scanning tunneling microscopy and density functional theory to elucidate the atomic-scale morphology of the system, suggesting a linear tri-Fe linkage between facing, coplanar tpy groups. Scanning tunneling spectroscopy reveals the highest occupied orbitals, with dominant contributions from states located at the Fe node, and ligand states that mostly contribute to the lowest unoccupied orbitals. This electronic structure yields potential for hosting photoinduced metal-to-ligand charge transfer in the visible/near-infrared. The formation of this unusual tpy/tri-Fe/tpy coordination motif has not been observed for wet chemistry synthetic methods and is mediated by the bottom-up on-surface approach used here, offering pathways to engineer the optoelectronic properties and reactivity of metal-organic nanostructures.

The emergence of graphene in recent years provides exciting avenues for achieving fast, reliable DNA/RNA sensing and sequencing. Here we explore the possibility of enhancing electronic fingerprints of nucleobases adsorbed on graphene by tuning the surface coverage and modifying molecular dipoles using first-principles calculations. We demonstrate that intermolecular interactions have a strong influence on the adsorption geometry and the electronic structure of the nucleobases, resulting in tilted configurations and a considerable modification of their electronic fingerprints in graphene. Our analysis reveals that the molecular dipole of the nucleobase molecules plays a dominant role in the electronic structure of graphene-nucleobase systems, inducing significant changes in the work functions and energy level alignments at the interface. These results highlight tunable control of the measured molecular signals in graphene by optimizing the surface contact between nucleobases and graphene. Our findings have important implications for identification and understanding of molecular fingerprints of DNA/RNA nucleobases in graphene-based sensing and sequencing methods.

Non-covalent functionalization via physisorption of organic molecules provides a scalable approach for modifying the electronic structure of graphene while preserving its excellent carrier mobilities. Here we investigated the physisorption of long-chain acenes, namely, hexacene and its fluorinated derivative perfluorohexacene, on bilayer graphene for tunable graphene devices using first principles methods. We find that the adsorption of these molecules leads to the formation of localized states in the electronic structure of graphene close to its Fermi level, which could be readily tuned by an external electric field. The electric field not only creates a variable band gap as large as 250 meV in bilayer graphene, but also strongly influences the charge redistribution within the molecule-graphene system. This charge redistribution is found to be weak enough not to induce strong surface doping, but strong enough to help preserve the electronic states near the Dirac point of graphene., 17 pages, 7 figures, supporting information