A multi-layered split ring metamaterial for a multiwavelength and tunable lasing spaser

We report a multiwavelength and tunable lasing spaser realized by a gain-assisted metamaterial. The metamaterial consists of three regularly spaced parallel arrays of weakly asymmetric metallic split rings, with the first-layered array located on the gain medium surface and the other two-layered arrays embedded in it. Our simulations demonstrate that the three-layered metamaterial can radiate three-wavelength electromagnetic waves with high Q factors and transmission enhancement, which can be tuned by varying the gain coefficient

An analog of double electromagnetically induced transparency with extremely high group indexes

An asymmetric metamaterial exhibiting an analog of double electromagnetically induced transparency (EIT) in the middle-infrared region is reported. The metamaterial consists of two-layered arrays of U-shaped rings embedded in a medium, with the lower layer rotated by 90◦. Our simulations demonstrate that both maximum group indexes are extremely high at the two EIT-like positions. The group index reaches about thrice the currently reported maximum value at the high-frequency EIT-like position. The transmittance at the two transparency positions also possesses extremely high Q factors, which is conducive to controlling the propagation of electromagnetic waves.Published versio

Fe₃O₄@Carbon Microsphere Supported Ag–Au Bimetallic Nanocrystals with the Enhanced Catalytic Activity and Selectivity for the Reduction of Nitroaromatic Compounds

The heterostructure Ag–Au bimetallic nanocrystals supported on Fe₃O₄@carbon composite microspheres were synthesized by one facile and controllable approach, wherein the Ag nanocrystals attached on the Fe₃O₄@carbon microspheres were prepared first and served as reductant for the galvanic replacement reaction with the Au precursor (HAuCl₄). Upon varying the feeding amounts of the Au precursor, the bimetallic compositions on the Fe₃O₄@carbon microsphere could be readily tuned resulting in a series of composite microspheres with different Au-to-Ag molar ratios. Subsequently, we thus investigated the catalytic activity and selectivity of the magnetic composite catalysts from two sides. First, 4-nitrophenol (4-NP) was applied as a model molecule to study the effect of different Au-to-Ag molar ratios on catalytic capabilities of the resulting composite microspheres. It was found that upon the addition of NaBH₄ the catalytic capability was markedly enhanced when the Au content was increased. The maximum activity parameter value reached 1580 s^–1 g^–1, which is far higher than those of known monometallic composites. Also, they could give the equally high yields for other nitroaromatic compounds with various substituents, irrespective of the linked electron-donating or electron-withdrawing groups. Second, the synergistic effects of the carbon substrate in the catalysis reaction were demonstrated. When compared with colloidal SiO₂, TiO₂, and poly­(styrene-<i>co</i>-acrylic acid) substrates, the carbon support not only facilitated the enhancement of the catalytic performance of the noble metal nanocrystals but was also more suitable for the <i>in situ</i> preparation of Au–Ag bimetallic nanocrystals using the GRR. Besides, the particles’ convenience in terms of their magnetic separability and outstanding reusability was validated through many successive reduction reaction cycles. In light of these unique characteristics, the Fe₃O₄@C@Ag–Au composite microspheres show promising and great potential for practical applications

Core-Double-Shell Fe₃O₄@Carbon@Poly(In^III-carboxylate) Microspheres: Cycloaddition of CO₂ and Epoxides on Coordination Polymer Shells Constituted by Imidazolium-Derived Al^III–Salen Bifunctional Catalysts

A hydrid microsphere Fe₃O₄@carbon@poly­(In^III-carboxylate) consisting of a cluster of Fe₃O₄ nanoparticles as the core, a carbon layer as the inner shell and a porous In^III–carboxylate coordination polymer as the outer shell was prepared and applied as a recyclable catalyst for the cycloaddition reaction of CO₂ and epoxides. Construction of this hybrid microsphere was achieved in the two steps, including (1) the one-pot solvothermal synthesis of Fe₃O₄@C particles with the abundant carboxylic groups on the carbon surface and (2) the subsequent growth of the outer shell polymers based on the precipitation coordination polymerization. Imidazolium-substituted Salen ligands were synthesized and chelated with the In­(III) ions using the terminal carboxylic groups. The coordination polymer shell was formed on the Fe₃O₄@C particles, and the structures including shell thickness, surface area and porosity could be varied by tuning the feeding ratios of the In­(III) ions and the ligands. The optimal structure of the coordination polymers showed a shell thickness of ca. 45 nm with ∼5 nm of mesopore, 174.7 m²/g of surface area and 0.2175 cm³/g of pore volume. In light of gas uptake capability, catalytic activity and magnetic susceptibility, cycloaddition of CO₂ with a series of epoxides were studied by using Al-complexed Fe₃O₄@C@In^III-[IL-Salen] microspheres. The results validated that the self-supporting catalytic layer with high surface area was of remarkable advantages, which were attributed from great increment of effective active sites and combination of nucleophilic/electrophilic synergistic property and CO₂ uptake capability. Therefore, these hybrid microspheres provided excellent catalytic activity, prominent selectivity to cyclic carbonates and outstanding recyclability with the assistance of an applied magnetic field

Peroxidase-Like Activity of Fe₃O₄@Carbon Nanoparticles Enhances Ascorbic Acid-Induced Oxidative Stress and Selective Damage to PC‑3 Prostate Cancer Cells

Ascorbic acid (AA) is capable of inhibiting cancer cell growth by perturbing the normal redox state of cells and causing toxic effects through the generation of abundant reactive-oxygen species (ROS). However, the clinical utility of AA at a tolerable dosage is plagued by a relatively low in vivo efficacy. This study describes the development of a peroxidase-like composite nanoparticle for use in an AA-mediated therapeutic strategy. On the basis of a high-throughput, one-pot solvothermal approach, Fe₃O₄@C nanoparticles (NPs) were synthesized and then modified with folic acid (FA) on the surface. Particular focus is concentrated on the assessment of peroxidase-like catalytic activity by a chromogenic reaction in the presence of H₂O₂. The carbon shell of Fe₃O₄@C NPs contains partially graphitized carbon and thus facilitates electron transfer in the catalytic decomposition of H₂O₂, leading to the production of highly reactive hydroxyl radicals. Along with magnetic responsiveness and receptor-binding specificity, the intrinsic peroxidase-like catalytic activity of Fe₃O₄@C-FA NPs pronouncedly promotes AA-induced oxidative stress in cancer cells and optimizes the ROS-mediated antineoplastic efficacy of exogenous AA. In vitro experiments using human prostate cancer PC-3 cells demonstrate that Fe₃O₄@C-FA NPs serve as a peroxidase mimic to create hydroxyl radicals from endogenous H₂O₂ that is yielded in response to exogenous AA via an oxidative stress process. The usage of a dual agent leads to the enhanced cytotoxicity of PC-3 cells, and, because of the synergistic effect of NPs, the administrated dosage of AA is reduced markedly. However, because normal cells (HEK 293T cells) appear to have a higher capacity to cope with additionally generated ROS than cancer cells, the NP–AA combination shows little damage in this case, proving that selective killing of cancer cells could be achieved owing to preferential accumulation of ROS in cancer cells. A possible ROS-mediated mechanism is discussed to elucidate the pharmaceutical profile of the NP–AA agent. In general, this foundational study reveals that the peroxidase-like nanomaterials are applicable for modulating oxidative stress for the selective treatment of cancer cells by generating a high level of endogenous ROS

Upregulation of a KN1 homolog by transposon insertion promotes leafy head development in lettuce

Leafy head is a unique type of plant architecture found in some vegetable crops, with leaves bending inward to form a compact head. The genetic and molecular mechanisms underlying leafy head in vegetables remain poorly understood. We genetically fine-mapped and cloned a major quantitative trait locus controlling heading in lettuce. The candidate gene (LsKN1) is a homolog of knotted 1 (KN1) from Zea mays Complementation and CRISPR/Cas9 knockout experiments confirmed the role of LsKN1 in heading. In heading lettuce, there is a CACTA-like transposon inserted into the first exon of LsKN1 (LsKN1▽). The transposon sequences act as a promoter rather than an enhancer and drive high expression of LsKN1▽. The enhanced expression of LsKN1▽ is necessary but not sufficient for heading in lettuce. Data from ChIP-sequencing, electrophoretic mobility shift assays, and dual luciferase assays indicate that the LsKN1▽ protein binds the promoter of LsAS1 and down-regulates its expression to alter leaf dorsoventrality. This study provides insight into plant leaf development and will be useful for studies on heading in other vegetable crops