There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Here, we present a review of the antibacterial effects of silver nanomaterials, including proposed antibacterial mechanisms and possible toxicity to higher organisms. For purpose of this review, silver nanomaterials include silver nanoparticles, stabilized silver salts, silver–dendrimer, polymer and metal oxide composites, and silver-impregnated zeolite and activated carbon materials. While there is some evidence that silver nanoparticles can directly damage bacteria cell membranes, silver nanomaterials appear to exert bacteriocidal activity predominantly through release of silver ions followed (individually or in combination) by increased membrane permeability, loss of the proton motive force, inducing de-energization of the cells and efflux of phosphate, leakage of cellular content, and disruption DNA replication. Eukaryotic cells could be similarly impacted by most of these mechanisms and, indeed, a small but growing body of literature supports this concern. Most antimicrobial studies are performed in simple aquatic media or cell culture media without proper characterization of silver nanomaterial stability (aggregation, dissolution, and re-precipitation). Silver nanoparticle stability is governed by particle size, shape, and capping agents as well as solution pH, ionic strength, specific ions and ligands, and organic macromolecules—all of which influence silver nanoparticle stability and bioavailability. Although none of the studies reviewed definitively proved any immediate impacts to human health or the environment by a silver nanomaterial containing product, the entirety of the science reviewed suggests some caution and further research are warranted given the already widespread and rapidly growing use of silver nanomaterials.

https://link.springer.com/content/pdf/10.1007%2Fs11051-010-9900-y.pdf

A review of the antibacterial effects of silver nanomaterials and potential implications for human health and the environment

Green synthesis of metal nanoparticles using plants

Synthesis of metallic nanoparticles using plant extracts.

In materials science, “green” synthesis has gained extensive attention as a reliable, sustainable, and eco-friendly protocol for synthesizing a wide range of materials/nanomaterials including
 metal/metal oxides nanomaterials, hybrid materials, and bioinspired materials. As such, green synthesis is regarded as an important tool to reduce the destructive effects associated with the traditional methods of synthesis for nanoparticles commonly utilized in laboratory and industry. In this review, we summarized the fundamental processes and mechanisms of “green” synthesis approaches, especially for metal and metal oxide [e.g., gold (Au), silver (Ag), copper oxide (CuO), and zinc oxide (ZnO)] nanoparticles using natural extracts. Importantly, we explored the role of biological components, essential phytochemicals (e.g., flavonoids, alkaloids, terpenoids, amides, and aldehydes) as reducing agents and solvent systems. The stability/toxicity of nanoparticles and the associated surface engineering techniques for achieving biocompatibility are also discussed. Finally, we covered applications of such synthesized products to environmental remediation in terms of antimicrobial activity, catalytic activity, removal of pollutants dyes, and heavy metal ion sensing.

/pdf/green-synthesis-of-metals-and-their-oxide-nanoparticles-4onh2g0i4w.pdf

‘Green’ synthesis of metals and their oxide nanoparticles: applications for environmental remediation

Biological synthesis of silver and gold nanoparticles using apiin as reducing agent

Conductive and stretchable electrodes that can be printed directly on a stretchable substrate have drawn extensive attention for wearable electronics and electronic skins. Printable inks that contain liquid metal are strong candidates for these applications, but the insulating oxide skin that forms around the liquid metal particles limits their conductivity. This study reveals that hydrogen doping introduced by ultrasonication in the presence of aliphatic polymers makes the oxide skin highly conductive and deformable. X-ray photoelectron spectroscopy and atom probe tomography confirmed the hydrogen doping, and first-principles calculations were used to rationalize the obtained conductivity. The printed circuit lines show a metallic conductivity (25,000 S cm–1), excellent electromechanical decoupling at a 500% uniaxial stretching, mechanical resistance to scratches and long-term stability in wide ranges of temperature and humidity. The self-passivation of the printed lines allows the direct printing of three-dimensional circuit lines and double-layer planar coils that are used as stretchable inductive strain sensors. Hydrogen doping and polymer adsorption at the oxide surface of liquid metal microparticles increase the conductivity and viscoplastic behaviour of the oxide, leading to liquid-metal-based printed circuits with stable resistance up to 500% strain.

/pdf/hydrogen-doped-viscoplastic-liquid-metal-microparticles-for-4m3fjnzgts.pdf

Hydrogen-doped viscoplastic liquid metal microparticles for stretchable printed metal lines.

A highly efficient, scalable, three step divergent synthesis of blocked isocyanate-terminated polyurethane dendrimers up to fourth generation (G4) has been developed avoiding the formation of free isocyanate. Amine-terminated polyurethane dendrimers were obtained as complementary functional materials in the second step. The blocked isocyanate moiety possessing easily cleavable blocking agents facilitated the dendrimer construction. Heat-curable adhesives based on G2 dendrimers tested on aluminum plates showed tensile shear strength of 2.41 MPa.

Amine- and blocked isocyanate-terminated polyurethane dendrimers: integrated synthesis, photophysical properties and application in a heat curable system

/pdf/folding-and-bending-planar-coils-for-highly-precise-soft-1ygjbhbrht.pdf

Folding and Bending Planar Coils for Highly Precise Soft Angle Sensing

The use of novel p-chlorophenyl and styrenyl-TEMPO terminated fourth generation (G4) polyurethane dendrimers doped with KI and I2 in conjunction with N3 dye as an efficient polymer electrolyte to improve the efficiency of nanocrystalline TiO2 dye-sensitized solar cell (DSSC) is described. Coordinative interactions and structural changes of these dendritic polymer electrolytes have been characterized by X-ray diffraction (XRD), electrical conductivity and scanning electron microscopic (SEM) studies. The XRD and SEM results confirm the amorphous structure of the electrolytes. The ionic conductivity of doped polyurethane dendrimers was remarkably high and the values were in the range of 1.5 × 10−3 Scm−1 to 1.1 × 10−3 Scm−1 at room temperature. As a consequence, the performance of the devices fabricated with dendrimers were appreciably good compared to that fabricated without dendrimers and in one case the photocurrent, photovoltage, fill factor and energy conversion efficiency achieved were 10.6 mA cm−2, 900 (mV), 0.51 and 8.5%, respectively, under simulated sunlight with AM 1.5 at 50 mW cm−2.

Selvaraj Veerapandian

Papers

Biological synthesis of silver and gold nanoparticles using apiin as reducing agent

Hydrogen-doped viscoplastic liquid metal microparticles for stretchable printed metal lines.

Amine- and blocked isocyanate-terminated polyurethane dendrimers: integrated synthesis, photophysical properties and application in a heat curable system

Folding and Bending Planar Coils for Highly Precise Soft Angle Sensing

Enhanced performance of a nanocrystalline dye-sensitized solar cell based on polyurethane dendrimers