Poly(vinylpyrrolidone)-Free Multistep Synthesis of Silver Nanoplates with Plasmon Resonance in the Near Infrared Range

Hybrid gum tragacanth/sodium alginate hydrogel reinforced with silver nanotriangles for bacterial biofilm inhibition

Biomaterial associated bacterial infections are indomitable to treatment due to the rise in antibiotic resistant strains, thereby triggering the need for new antibacterial agents. Herein, composite bactericidal hydrogels were formulated by incorporating silver nanotriangles (AgNTs) inside a hybrid polymer network of Gum Tragacanth/Sodium Alginate (GT/SA) hydrogels. Physico-chemical examination revealed robust mechanical strength, appreciable porosity and desirable in vitro enzymatic biodegradation of composite hydrogels. The antibacterial activity of AgNT-hydrogel was tested against planktonic and biofilm-forming Gram-negative (Escherichia coli and Pseudomonas aeruginosa) and Gram-positive (Staphylococcus aureus) bacteria. For all the strains, AgNT-hydrogel showed a dose-dependent decrease in bacterial growth. The addition of AgNT-hydrogels (40-80 mg ml^-1) caused 87% inhibition of planktonic biomass and up to 74% reduction in biofilm formation. Overall, this study proposes a promising approach for designing antibacterial composite hydrogels to mitigate various forms of bacterial infection.

Ferric Chloride-Induced Synthesis of Silver Nanodisks with Considerable Activity for the Reduction of 4-Nitrophenol

Silver nanodisks (AgNDs) have been successfully synthesized by using ferric chloride as an auxiliary agent in the presence of polyvinylpyrrolidone and N,N-dimethylformamide as both a solvent and a reducing agent. The mass ratio of reactants, temperature, and time were demonstrated to be the key factors determining the morphology of the product, and the conversion of Fe3+/Fe2+ ions played an important role in increasing the ratio of silver nanosheets (AgNSs). As the reaction prolonged, the etching effect of Cl- ions on the tips of AgNSs became more and more obvious, which made the obtained typical polygonal AgNSs turn into AgNDs eventually. In addition, the prepared AgNDs exhibited a considerable catalytic activity in the reduction of 4-nitrophenol.

A novel method based on Ag-Au nanorings with tunable plasmonic properties for the sensitive detection of amantadine

To prevent the toxic effect of amantadine (AMD) on humans, a sensitive and direct detection method is required. The conventional enzyme-linked immunosorbent assay (ELISA) usually shows a monochromatic gradient color variation with the concentration of the target; hence, it is not a sensitive method for naked-eye detection. In this work, Ag-Au nanorings with highly tunable plasmon properties were synthesized as colorimetric nanosensors. The growth of Ag on the hollow nanorings led to rich color variations. Ag-Au nanorings were integrated into ELISA for the sensitive detection of AMD with the naked eye. The proposed method showed high sensitivity for the qualitative and quantitative detection of AMD, the visible cut-off value (0.2 ng mL^-1) and limit of detection (0.071 ng mL^-1) were 10-fold and 4.7-fold lower, respectively, than those of conventional ELISA. This method showed a linear range of 0.08-2 ng mL^-1 and 4-12 ng mL^-1. The detection results of this method on 100 samples (food samples and municipal water) agreed well with those of liquid chromatography-tandem mass spectrometry. The proposed plasmonic ELISA has high sensitivity, easy operation, and naked-eye readout.

Wet-chemical synthesis of two-dimensional metal nanomaterials for electrocatalysis

Two-dimensional (2D) metal nanomaterials have gained ever-growing research interest owing to their fascinating physicochemical properties and promising application, especially in the field of electrocatalysis. In this review, we briefly introduce the recent advances in wet-chemical synthesis of 2D metal nanomaterials. Subsequently, the catalytic performances of 2D metal nanomaterials in a variety of electrochemical reactions are illustrated. Finally, we summarize current challenges and highlight our perspectives on preparing high-performance 2D metal electrocatalysts.

Non-toxic near-infrared light-emitting diodes

Harnessing cost-efficient printable semiconductor materials as near-infrared (NIR) emitters in light-emitting diodes (LEDs) is extremely attractive for sensing and diagnostics, telecommunications, and biomedical sciences. However, the most efficient NIR LEDs suitable for printable electronics rely on emissive materials containing precious transition metal ions (such as platinum), which have triggered concerns about their poor biocompatibility and sustainability. Here, we review and highlight the latest progress in NIR LEDs based on non-toxic and low-cost functional materials suitable for solution-processing deposition. Different approaches to achieve NIR emission from organic and hybrid materials are discussed, with particular focus on fluorescent and exciplex-forming host-guest systems, thermally activated delayed fluorescent molecules, aggregation-induced emission fluorophores, as well as lead-free perovskites. Alternative strategies leveraging photonic microcavity effects and surface plasmon resonances to enhance the emission of such materials in the NIR are also presented. Finally, an outlook for critical challenges and opportunities of non-toxic NIR LEDs is provided.

Resolving the stacking fault structure of silver nanoplates

The stacking fault structure (SFT) is the key to understanding the symmetry breaking of fcc nanocrystals and the origin of two-dimensional (2D) anisotropic growth of nanoplates. After resolving the SFT in Ag nanoplates under aberration-corrected transmission electron microscope (TEM) observations, it is found that there are three basic stacking faults, namely, twinned stacking fault (SF-t), a layer missed stacking fault (SF-m) and a layer inserted stacking fault (SF-i). The SFT is composed of one or a combination of two or all of the three kinds of stacking faults with a total number varying from 4 to 9. It has been demonstrated that the SFT could generate concave faces, step faces and (100) faces in the lateral directions, which provides sites for adding-atoms with a higher coordination number than on the top and bottom flat (111) faces, and results in the anisotropic growth along the 2D direction. Additionally, Ag nanoplates fall into either center symmetry or mirror symmetry when the corresponding number is even or odd. The center symmetry and mirror symmetry with different side face arrangements in turn manipulate the shape evolution to cubes and bipyramids, respectively. Our study provides a comprehensive understanding of the formation and growth of 2D metal nanomaterials.

Green synthesis of silver nanoplates using the special category of plant leaves showing the lotus effect

This paper reports the first ever green synthesis of silver nanoplates using plant leaves having the special feature of showing the lotus effect. Eichhornia crassipes and Colocasia esculenta plant leaves were chosen for the purpose. The aqueous leaf extract of these plants was used as a reducing as well as stabilizing agent in the hydrothermal synthesis of silver nanoplates using silver nitrate as the precursor. Well dispersed silver nanoplates were formed. The appearance of two SPR (Surface Plasmon Resonance) bands corresponding to in-plane and out of plane vibration confirmed the formation of anisotropic nanostructures. The blue shift in peaks of the nanostructures in UV-visible spectra gave information about the stability of the nanoplates with time. Dynamic Light Scattering (DLS) and powder XRD were used to evaluate the ultimate average diameter and crystal structure of these nanostructures respectively. FESEM/EDX and HRTEM/SAED images also confirmed the formation of silver nanoplates. The FT-IR spectra helped to identify the reducing and stabilizing component of plant leaves extract in the formation of 2-D nanostructures. Preliminary antibacterial activity was examined using these nanoplates. A significant zone of inhibition was observed for S. aureus, a Gram positive bacterium.

Synthesis of large gold nanoparticles with deformation twinnings by one-step seeded growth with Cu(ii)-mediated Ostwald ripening for determining nitrile and isonitrile groups

In this work, uniform and large gold nanoparticles (Au NPs) including quasi-spherical (QS) Au NPs with average diameters of 70 to 196 nm and trisoctahedral (TOH) Au NPs with average diameters of 140 to 195 nm were successfully synthesized by controlling the concentration of Cu2+ ions and the particle number of 3 nm Au-NP seeds, respectively, using a one-step seeded growth method with Cu2+-mediated Ostwald ripening. It is found that because of the concentration-dependent under-potential deposition of Cu2+ ions (CuUPD), 3 nm Au-NP seeds are firstly changed into Au NPs with a controlled QS- or TOH shape at the initial growth stage, followed by the conformal growth of Au atoms onto the initially formed Au NPs due to Cu2+-mediated Ostwald ripening, in which the extra Au atoms come from the dissolution of in situ Au nuclei by the unavoidable self-nucleation. Moreover, the as-prepared QS Au NPs with a rough surface exhibit a better SERS performance for physically adsorbed probes (crystal violet, CV) than the TOH Au NPs with sharp tips and with a comparable size. Furthermore, the as-prepared QS Au NPs can be used to distinguish nitrile and isonitrile groups by surface-enhanced Raman scattering (SERS) due to the presence of deformation twinnings. Thus, the as-prepared QS Au NPs with a rough surface and deformation twinnings can be further used as templates for the fabrication of bimetallic materials with multi-functionalities.

Molecular-Level Control over Plasmonic Properties in Silver Nanoparticle/Self-Assembling Peptide Hybrids

The plasmonic properties of silver nanoparticle (AgNP) arrays are directly controlled by AgNP size, shape, and spatial arrangement. Reported here is a strategy to prepare chiral AgNP arrays templated by two constitutionally isomeric aromatic peptide amphiphiles (APAs), KSC'EKS and C'EKSKS (KS = S-aroylthiooxime-modified lysine, C' = citrulline, and E = glutamic acid). In phosphate buffer, both APAs initially self-assembled into nanoribbons with a similar geometry. However, in the presence of silver ions and poly(sodium 4-styrenesulfonate) (PSSS), one of the nanoribbons (KSC'EKS) turned into nanohelices with a regular twisting pitch, while the other (C'EKSKS) remained as nanoribbons. Both were used as templates for synthesis of arrays of ∼8 nm AgNPs to understand how small changes in molecular structure affect the plasmonic properties of these chiral AgNP/APA hybrids. Both hybrids showed improved colloidal stability compared to pure AgNPs, and both showed enhanced sensitivity as surface-enhanced Raman spectroscopy (SERS) substrates for model analytes, with nanohelices showing better SERS performance compared to their nanoribbon counterparts and pure AgNPs.

Bimetal composites for photocatalytic reduction of CO2 to CO in the near-infrared region by the SPR effect

A major challenge in the field of photocatalytic carbon dioxide (CO₂) reduction is to design catalyst systems featuring high selectivity for CO production, long-term stability and a composition of Earth-abundant elements.

Recent progress in the synthesis and applications of 2D metal nanosheets

The design and controlled synthesis of two-dimensional (2D) nanomaterials have been widely studied because the properties and functions of nanomaterials are highly dependent on their sizes, shapes, and dimensionalities. For instance, 2D metal nanosheets (2DMNSs) have attracted a significant amount of attention owing to their interesting properties, which are absent in corresponding bulk counterparts, and they have been confirmed to have potential applications in electrocatalysis, optics, and biomedicine. However, because of the close-packed structures of metals, the large-scale fabrication of 2DMNSs is challenging. In this review, we have outlined the research progress in the field of 2DMNSs, including the typical synthesis approaches and newly developed methods, as well as promising applications of the materials reported in recent years. Moreover, some preliminary and promising strategies to further improve the properties of 2DMNSs and some insights for the development of the field have been included.

Spectral-Selective Plasmonic Polymer Nanocomposites Across the Visible and Near-Infrared

State-of-the-art commercial light-reflecting glass is coated with a metalized film to decrease the transmittance of electromagnetic waves. In addition to the cost of the metalized film, one major limitation of such light-reflecting glass is the lack of spectral selectivity over the entire visible and near-infrared (NIR) spectrum. To address this challenge, we herein effectively harness the transmittance, reflectance, and filtration of any wavelength across the visible and NIR, by judiciously controlling the planar orientation of two-dimensional plasmonic silver nanoplates (AgNPs) in polymer nanocomposites. In contrast to conventional bulk polymer nanocomposites where plasmonic nanoparticles are randomly mixed within a polymer matrix, our thin-film polymer nanocomposites comprise a single layer, or any desired number of multiple layers, of planarly oriented AgNPs separated by tunable spacings. This design employs a minimal amount of metal and yet efficiently manages light across the visible and NIR. The thin-film plasmonic polymer nanocomposites are expected to have a significant impact on spectral-selective light modulation, sensing, optics, optoelectronics, and photonics.

One-Step Synthesis of Quadrilateral-Shaped Silver Nanoplates with Lamellar Structures Tuned by Amylopectin Derivatives

Polymers or small molecules with functional groups were always employed to synthesize two-dimensional (2D) silver nanostructures, but the polysaccharides and derivatives have rarely been used for their preparation, let alone of uniform quadrilateral shapes. Herein, amylopectin derivatives containing concentrated carboxyl groups were first used for the synthesis of uniform 2D quadrilateral silver nanoplates (QAgNPs) with lamellar structure. As a native hyperbranched polysaccharide, amylopectin was esterified with 10-undecenoyl chloride and then modified via thiol-ene click chemistry to introduce high amount and high density of carboxyl groups. Then, QAgNPs were synthesized via UV photoreduction in the presence of the resultant amylopectin 11-((3-carboxyl)ethylthio)undecanoate (APUE3-MPA) in water-tetrahydrofuran binary system. QAgNPs showed novel uniform quadrilateral shapes with lamellar structure, as verified by their wide-angle X-ray scattering patterns. The average interlayer distance was around 1.3 nm, whereas the average edge lengths of QAgNPs varied between 0.29 ± 0.07 and 1.09 ± 0.25 μm. The concentration of APUE3-MPA and the amount of water in the reaction system strongly affected the shapes of QAgNPs. Thus, the reaction system and the arrangement of numerous carboxyl groups were the key factors for the formation of lamellar-structured QAgNPs.