Single-Molecule Nanocatalysis Reveals Catalytic Activation Energy of Single Nanocatalysts

By monitoring the temperature-dependent catalytic activity of single Au nanocatalysts for a fluorogenic reaction, we derive the activation energies via multiple methods for two sequential catalytic steps (product formation and dissociation) on single nanocatalysts. The wide distributions of activation energies across multiple individual nanocatalysts indicate a huge static heterogeneity among the individual nanocatalysts. The compensation effect and isokinetic relationship of catalytic reactions are observed at the single particle level. This study exemplifies another function of single-molecule nanocatalysis and improves our understanding of heterogeneous catalysis

Observing the Heterogeneous Electro-redox of Individual Single-Layer Graphene Sheets

Electro-redox-induced heterogeneous fluorescence of an individual single-layer graphene sheet was observed in real time by a total internal reflection fluorescence microscope. It was found that the fluorescence intensity of an individual sheet can be tuned reversibly by applying periodic voltages to control the redox degree of graphene sheets. Accordingly, the oxidation and reduction kinetics of an individual single-layer graphene sheet was studied at different voltages. The electro-redox-induced reversible variation of fluorescence intensity of individual sheets indicates a reversible band gap tuning strategy. Furthermore, correlation analysis of redox rate constants on individual graphene sheets revealed a redox-induced spatiotemporal heterogeneity or dynamics of graphene sheets. The observed controllable redox kinetics can rationally guide the precise band gap tuning of individual graphene sheets and then help their extensive applications in optoelectronics and devices for renewable energy

The effect of iodide on the synthesis of gold nanoprisms

<div><p>It has been known that the iodide (I⁻) anions are necessary for the production of high-quality Au nanoprisms. Based on a previously reported seed-mediated synthesis of triangular gold nanoprisms, herein, we further optimised the synthesis process by varying the concentration of added NaI and seeds, respectively, to get high-quality (size-monodisperse, tip-sharp and purity-high) Au nanoprisms. The results show that the ratio between the concentration of I⁻ and seeds is a very sensitive parameter to control the quality (size-monodispersity, tip-sharpness and purity) of Au nanoprisms.</p></div

The performance of MR perfusion-weighted imaging for the differentiation of high-grade glioma from primary central nervous system lymphoma: A systematic review and meta-analysis

<div><p>It is always a great challenge to distinguish high-grade glioma (HGG) from primary central nervous system lymphoma (PCNSL). We conducted a meta-analysis to assess the performance of MR perfusion-weighted imaging (PWI) in differentiating HGG from PCNSL. The heterogeneity and threshold effect were evaluated, and the sensitivity (SEN), specificity (SPE) and areas under summary receiver operating characteristic curve (SROC) were calculated. Fourteen studies with a total of 598 participants were included in this meta-analysis. The results indicated that PWI had a high level of accuracy (area under the curve (AUC) = 0.9415) for differentiating HGG from PCNSL by using the best parameter from each study. The dynamic susceptibility-contrast (DSC) technique might be an optimal index for distinguishing HGGs from PCNSLs (AUC = 0.9812). Furthermore, the DSC had the best sensitivity 0.963 (95%CI: 0.924, 0.986), whereas the arterial spin-labeling (ASL) displayed the best specificity 0.896 (95% CI: 0.781, 0.963) among those techniques. However, the variability of the optimal thresholds from the included studies suggests that further evaluation and standardization are needed before the techniques can be extensively clinically used.</p></div

Regeneration and Enhanced Catalytic Activity of Pt/C Electrocatalysts

By adding pure carbon support to improve the redispersion of platinum (Pt), a sintered Pt/C electrocatalyst for methanol electrooxidation was effectively regenerated in activity and doubled in amount on the basis of a one-step liquid oxychlorination. The apparent activity (mA mg_cata.^–1) of the optimal Pt/C regenerated (Pt 3.3 wt %) is close to the initial fresh Pt/C (Pt 10 wt %) and about two times that of fresh Pt/C (Pt 3.3 wt %), making Pt utilization doubled and then the resource-limited Pt potentially sustainable. The new nucleation of metal atoms on added pure support surface was found to be the key for both the improved redispersion of metal nanoparticles and the effective regeneration of catalytic activity in situ

Summary Receiver-Operating Characteristic curve (SROC).

<p>(A) Overall group; (B) DSC group; (C) ASL group; (D) DCE group. AUC area under the curve.</p

Methodological quality analysis of the 12 eligible studies using QUADAS-2 tool.

<p>Methodological quality analysis of the 12 eligible studies using QUADAS-2 tool.</p

Funnel plot of publication bias.

<p>(A) Overall group; (B) DSC group; (C) ASL group; (D) DCE group.</p

Forest plot showing the sensitivity and specificity of different groups for the differentiation of HGGs from PCNSLs.

<p>(A) Overall group; (B) DSC group; (C) ASL group; (D) DCE group.</p

Single-Molecule Nanocatalysis of Pt Nanoparticles

Because of the inhomogeneous structure of nanoparticles, many underlying catalytic details of these catalysts are hidden in the ensemble-averaged measurements. The single-molecule approach enables studying the catalytic behavior of nanoparticles at the single-particle level in single-turnover resolution. Here, on the basis of such a method, we study the catalytic behaviors of individual Pt nanoparticles to reveal the catalytic properties of nanoparticles of the product formation and desorption process. It is found that the catalytic reaction on Pt nanoparticles follows competitive mechanism in product formation process, while the product desorption process shows no selectivity between the indirect and direct desorption pathways. Moreover, the dynamic heterogeneity of Pt nanoparticles in product formation and desorption process is revealed to be due to the catalysis-induced surface restructuring. Surprisingly, it is found both experimentally and theoretically that the tiny difference in substrate molecules could lead to a huge difference in surface restructuring even on the same type of nanoparticle