Fabrication of Au25(SG)18–ZIF‐8 Nanocomposites: A Facile Strategy to Position Au25(SG)18 Nanoclusters Inside and Outside ZIF‐8

Multifunctional composite materials are currently highly desired for sustainable energy applications. A general strategy to integrate atomically precise Au₂₅(SG)₁₈ with ZIF‐8 (Zn(MeIm)₂, MeIm = 2‐methylimidazole), is developed via the typical Zn‐carboxylate type of linkage. Au₂₅(SG)₁₈ are uniformly encapsulated into a ZIF‐8 framework (Au₂₅(SG)₁₈@ZIF‐8) by coordination‐assisted self‐assembly. In contrast, Au₂₅(SG)₁₈ integrated by simple impregnation is oriented along the outer surface of ZIF‐8 (Au₂₅(SG)₁₈/ZIF‐8). The porous structure and thermal stability of these nanocomposites are characterized by N₂ adsorption–desorption isothermal analysis and thermal gravimetric analysis. The distribution of Au₂₅(SG)₁₈ in the two nanocomposites is confirmed by electron microscopy, and the accessibility of Au₂₅(SG)₁₈ is evaluated by the 4‐nitrophenol reduction reaction. The as‐prepared nanocomposites retain the high porosity and thermal stability of the ZIF‐8 matrix, while also exhibiting the desired catalytic and optical properties derived from the integrated Au₂₅(SG)₁₈ nanoclusters (NCs). Au₂₅(SG)₁₈@ZIF‐8 with isolated Au₂₅ sites is a promising heterogenous catalyst with size selectivity imparted by the ZIF‐8 matrix. The structural distinction between Au₂₅(SG)₁₈@ZIF‐8 and Au₂₅(SG)₁₈/ZIF‐8 determines their different emission features, and provides a new strategy to adjust the optical behavior of Au₂₅(SG)₁₈ for applications in bioimaging and biotherapy.     

Developing a millifluidic platform for the synthesis of ultrasmall nanoclusters: ultrasmall copper nanoclusters as a case study

The future of lab-on-a-chip devices for the synthesis of nanomaterials hinges on the successful development of high-throughput methods with better control over their size. While significant effort in this direction mainly focuses on developing "difficult to fabricate" complex microfluidic reactors, scant attention has been paid to the "easy to fabricate" and simple millifluidic systems that could provide the required control as well as high throughput. By utilizing numerical simulation of fluids within the millifluidic space at different flow rates, the results presented here show velocity profiles and residence time distributions similar to the case of microfluidics. By significantly reducing the residence time and residence time distribution, a continuous flow synthesis of ultrasmall copper nanoclusters (UCNCs) with exceptional colloidal stability is achieved. In-situ synchrotron-radiation-based X-ray absorption spectroscopy (XAS) reveal that the as-prepared clusters are about 1 nm, which is further supported by transmission electron microscopy and UV-vis spectroscopy studies. The clusters reported here are the smallest ever produced using a lab-on-a-chip platform. When supported on silica, they are found to efficiently catalyze C-H oxidation reactions, hitherto unknown to be catalyzed by Cu. This work suggests that a millifluidic platform can be an inexpensive, versatile, easy-to-use, and powerful tool for nanoparticle synthesis in general, and more specifically for ultrasmall nanoclusters (UNCs).     

Nano-C(60) : a novel, effective, fluorescent sensing platform for biomolecular detection

Water-soluble nano-C(60) can serve as a novel, effective, fluorescent sensing platform for biomolecular detection with high sensitivity and selectivity. In this paper, fluorescent detection of DNA and thrombin via nano-C(60) is demonstrated for the first time. The principle of the assay lies in the fact that the adsorption of the fluorescently labeled single-stranded DNA (ssDNA) probe by nano-C(60) leads to substantial fluorescence quenching. In the presence of a target, the biomolecular mutual interaction suppresses this quenching, signaling the existence of the target. This sensing system rivals graphene oxide but is superior to other carbon-structure-based systems. The present method can also achieve multiplex DNA detection and withstand the interference from human blood serum.     

(Lysozyme type VI)-stabilized Au8 clusters: synthesis mechanism and application for sensing of glutathione in a single drop of blood

This paper presents a one-pot approach for preparing highly fluorescent Au(8) clusters by reacting the Au(3+) precursor solution with lysozyme type VI (Lys VI) at pH 3. The fluorescence band of (Lys VI)-stabilized Au(8) clusters is centered at 455 nm on the excitation at 380 nm. Blue-emitting Au(8) clusters have a high quantum yield (～56%), two fluorescence lifetimes, and a rare amount of Au(+) on the surface of the Au core. When the pH of a solution of Au(8) clusters increases suddenly to 12, the Au(8) clusters gradually convert to Au(25) clusters over time. This conversion is also observed in the case of (Lys VI)-directed synthesis of Au(25) clusters at pH 12. The pH-induced conversion of Au(8) to Au(25) clusters suggests that the size of (Lys VI)-stabilized gold nanoclusters (AuNCs) relies on the secondary structure of Lys VI, which is susceptible to pH change. Based on these results and previous literature, this paper proposes the possible mechanism for growing (Lys VI)-stabilized Au(8) and Au(25) clusters. Additionally, (Lys VI)-stabilized Au(8) clusters could sense glutathione (GSH) through GSH-induced core-etching of Au(8) clusters; the limit of detection at a signal-to-noise ratio of 3 for GSH is determined to be 20 nm. Except for cysteine, the selectivity of (Lys VI)-stabilized Au(8) clusters for GSH over amino acids is remarkably high. The practicality of using Au(8) clusters to determine the concentration of GSH in a single drop of blood is also validated.     

A new parameter for (normalized) evaluation of H-index: countries as a case study

It is known that the H-indexes of individuals, research groups, institutions, scientific journals, and countries strongly depend on the field of study, slowly increase with the number of publications, N, and can be described by empirical power-law functions of the type H?=?C?×?N^a (C and a are constants and depend on the specific field being analyzed). In this paper, we use this function and propose a new index [Montazerian–Zanotto–Eckert (MZE)], which is normalized by the number of publications and typically varies from ??1 to +?1, to characterize the relative standing of a research group, institution, or author to those of his/her peer groups. Due to the rich statistics available, as an example, here we analyzed and tested the new parameter against the citation-related performance (H-index) of countries. We found that the MZE index readily distinguishes between countries that stand above or below the average (for any given number of publications). Generally, publications of countries with a positive MZE index are more interesting or visible than the average. Analyzing publication output in this manner instead of the H-index allows for a less biased comparison between researchers, journals, universities, or countries for any particular combination of H-index and publication output.

     

Science and power: Francoist Spain (1939–1975) as a case study

This paper takes Franco's Spain to be a powerful case study for analyzing the ways in which power shapes science and technology and is shaped by them in return. Spain was the last country in Western Europe to establish closer links with any of the international cooperative institutions emerging after WWII. As such, developments internal to Spanish society were quite autonomous and relatively free from foreign influences. The paper focuses first on the brand new, powerful institution that the Francoist regime created to promote scientific research under tight political control, the Consejo Superior de Investigaciones Científicas. Next it turns to applied science and technology, top priorities for the regime's state‐supported programs of industrialization. They were implemented through the politically and financially powerful Instituto Nacional de Industria. Using diplomatic sources, the paper next argues that, until the late 1950s, Spain maintained substantial political and economic isolation essentially because the regime bet on autarkic policies and a model of largely isolated development. In this model, it was crucial for the regime to develop its own technological and scientific resources. Finally, the paper examines how the regime fostered a new Spanish identity in which science had a new role.     

Two‐Dimensional Self‐Organization of an Ordered Au Silicide Nanowire Network on a Si(110)‐16 × 2 Surface

A well‐ordered two‐dimensional (2D) network consisting of two crossed Au silicide nanowire (NW) arrays is self‐organized on a Si(110)‐16 × 2 surface by the direct‐current heating of ≈1.5 monolayers of Au on the surface at 1100 K. Such a highly regular crossbar nanomesh exhibits both a perfect long‐range spatial order and a high integration density over a mesoscopic area, and these two self‐ordering crossed arrays of parallel‐aligned NWs have distinctly different sizes and conductivities. NWs are fabricated with widths and pitches as small as ≈2 and ≈5 nm, respectively. The difference in the conductivities of two crossed‐NW arrays opens up the possibility for their utilization in nanodevices of crossbar architecture. Scanning tunneling microscopy/spectroscopy studies show that the 2D self‐organization of this perfect Au silicide nanomesh can be achieved through two different directional electromigrations of Au silicide NWs along different orientations of two nonorthogonal 16 × 2 domains, which are driven by the electrical field of direct‐current heating. Prospects for this Au silicide nanomesh are also discussed.