Micron-Scale Fabrication of Ultrathin Amorphous Copper Nanosheets Templated by DNA Scaffolds

Synthesis of fluorescent AuNCs with RNA as template

Although nucleic acids have been widely used as templates for the synthesis of nanomaterials, the synthesis of RNA-templated gold nanoclusters (AuNCs) has not been explored. In this work, we developed a simple strategy for synthesis of RNA-templated fluorescent AuNCs. We first evaluated the adsorption of different nucleoside monophosphates (NMP) on gold atoms. Our density function theory simulation and isothermal titration calorimetry measurements demonstrated that adenosine monophosphate (AMP) is a superior gold binder than other NMPs or deoxyadenosine monophosphate. Afterwards, NMP-templated synthesis of AuNCs was conducted in various pH environments, and our results indicated that bright green light-emitting AMP-templated AuNCs can be obtained at pH ∼6.0. In order to study the synthesis mechanism of AuNCs, we investigated the effects of reducing agent type and addition time, and the negative charge carried by template nucleotides on the fluorescence of AuNCs. Finally, we extended the template AMP into RNA hairpin structure, the fluorescence intensity was the highest when the cyclic bases were poly 16 A. This study opens new routes to synthesize fluorescent AuNCs using RNA templates.

Self-Organized Gradually Single-Atom-Layer of Metal Osmium for an Unprecedented Hydrogen Production from Seawater

Atomic thick two-dimensional (2D) materials with exciting physical, chemical, and electronic properties are gaining increasing attention in next-generation science and technology, showing great promise in catalysis and energy science. However, the precise design and synthesis of efficient catalytic systems based on such materials still face many difficulties, especially in how to control the preparation of structurally determined, highly active, atomic-scale distribution of material systems. Here, we report that a highly active zerovalent osmium single-atom-layer with a thickness of single atom size has been successfully and controllably self-organized on the surface of 2D graphdiyne (GDY) material. Detailed characterizations showed that the incomplete charge transfer effect between the Os atoms and GDY not only stabilized the catalytic system but also improved the intrinsic activity, making the Gibbs free energy reach the best and resulting in remarkable performance with a small overpotential of 49 mV at 500 mA cm-2, large specific j0 of 18.6 mA cm-2, and turnover frequency of 3.89 H2 s-1 at 50 mV. In addition, the formation of sp-C-Os bonds guarantees the high long-term stability of 800 h at a large current density of 500 mA cm-2 in alkaline simulated seawater.

DNA Framework-Templated Fabrication of Ultrathin Electroactive Gold Nanosheets

Generally, two-dimensional gold nanomaterials have unique properties and functions that offer exciting application prospects. However, the crystal phases of these materials tend to be limited to the thermodynamically stable crystal structure. Herein, we report a DNA framework-templated approach for the ambient aqueous synthesis of freestanding and microscale amorphous gold nanosheets with ultrathin sub-nanometer thickness. We observe that extended single-stranded DNA on DNA nanosheets can induce site-specific metallization and enable precise modification of the metalized nanostructures at predefined positions. More importantly, the as-prepared gold nanosheets can serve as an electrocatalyst for glucose oxidase-catalyzed aerobic oxidation, exhibiting enhanced electrocatalytic activity (~3-fold) relative to discrete gold nanoclusters owing to a larger electrochemical active area and wider band gap. The proposed DNA framework-templated metallization strategy is expected to be applicable in a broad range of fields, from catalysis to new energy materials.

Copper Nanosheet-Based Wash-Free Fluorescence Imaging of Cancer Cells

Near-infrared fluorescence (NIRF) probes greatly facilitate in vivo imaging of various biologically important species. However, there are several significant limitations such as consuming washing steps, photobleaching, and low signal intensity. Herein, we synthesized fluorescent copper nanosheets templated with DNA scaffolds (DNS/CuNSs). We employ them and Cy5.5 of the fluorescence resonance energy transfer (FRET) system, which have a larger Stokes shift (∼12-fold) than the traditional NIRF dye Cy5.5. Based on their excellent fluorescence properties, we employ DNS/CuNSs-Cy5.5 for fluorescence probes in cancer cell imaging. Compared with the free Cy5.5 fluorescence probe, the novel fluorescence imaging probe implements wash-free imaging and exhibits enhanced anti-photobleaching ability (∼5.5-fold). Moreover, the FRET system constructed by DNS/CuNSs has a higher signal amplification ability (∼4.17-fold), which is more similar to that of Cu nanoclusters prepared with DNA nanomonomers as a template. This work provides a new idea for cancer cell MCF-7 imaging and is expected to promote the development of cancer cell fluorescence imaging.

Slowly Removing Surface Ligand by Aging Enhances the Stability of Pd Nanosheets toward Electron Beam Irradiation and Electrocatalysis

Surface ligands play an important role in shape-controlled growth and stabilization of colloidal nanocrystals. Their quick removal tends to cause structural deformation and/or aggregation to the nanocrystals. Herein, we demonstrate that the surface ligand based on poly(vinylpyrrolidone) (PVP) can be slowly removed from Pd nanosheets (NSs, 0.93±0.17 nm in thickness) by simply aging the colloidal suspension. The aged Pd NSs show well-preserved morphology, together with significantly enhanced stability toward both e-beam irradiation and electrocatalysis (e.g., ethanol oxidation). It is revealed that the slow desorption of PVP during aging forces the re-exposed Pd atoms to reorganize, facilitating the surface to transform from being nearly perfect to defect-rich. The resultant Pd NSs with abundant defects no longer rely on surface ligand to stabilize the atomic arrangement and thus show excellent structural and electrochemical stability. This work provides a facile and effective method to maintain the integrity of colloidal nanocrystals by slowly removing the surface ligand.

Amorphous Copper-Based Nanoparticles with Clusterization-Triggered Phosphorescence for Ultrasensing 2,4,6-Trinitrotoluene

Amorphous metal-based nanostructures have attracted great attention recently due to their facilitative electron transfer and abundant reactive sites, whereas it remains enigmatic as to whether amorphous copper-based nanoparticles (CuNPs) can be achieved. Here, for synthesizing amorphous CuNPs, glutathione is adopted as a ligand to inhibit the nucleation and crystallization process via its electrostatic repulsion. By subtly tailoring the solvent polarity, not only can amorphous glutathione-functionalized CuNPs (GSH-CuNPs) with phosphorescent performance be achieved after transferring the non-conjugation of GSH ligand to through-space conjugation, namely clusterization-triggered emission, but also the phosphorescence-off of GSH-CuNPs toward 2,4,6-trinitrotoluene (TNT) can be realized by the photoinduced electron-transfer process through the hydrogen bond channel, which is established between carboxyl and amino groups of GSH-CuNPs with the nitryl group of TNT. Benefitting from the intrinsic superiorities of the amorphous CuNPs, desired phosphorescence and detection performances of GSH-CuNPs toward airborne TNT microparticulates are undoubtedly realized, including high quantum yield (13.22%), excellent specificity in 33 potential interferents, instantaneous response, and ultralow detection limit (1.56 pg). The present GSH-CuNPs are expected to stretch amorphous metal-based nanostructures and deepen the insights into amorphous materials for optical detection.