Plasmonic Ag nanoparticles via environment-benign atmospheric microplasma electrochemistry

Synthesis of Gold-PVP Nanostructured Composites by Microplasma: A Test to Study Their Inhibiting Tendency of Avian Influenza Virus Activity

Gold–polymer nanostructured composites have a great potential in the biomedical and advanced materials field as an antimicrobial agent against various pathogens, especially viruses. In the present work, gold and gold-PVP colloids have been prepared by the electrochemical reduction of hydrogen tetrachlorauric acid (HAuCl4·3H2O) precursor. The atmospheric pressure microplasma technique was used as a reducing agent, while D-Fructose was used as a stabilizing agent in the synthesis process. X-ray Diffraction (XRD) confirmed the crystalline behavior of both gold nanostructured particles and gold-PVP nanocomposites. The morphology of the nanoparticles was examined by SEM. The absorption characteristic peaks at 541 nm and 542 nm in UV-Vis spectra confirmed the surface plasmon resonance in gold nanostructured particles and gold-PVP nanostructured composites, respectively. Dynamic light scattering studies with percentage intensity distribution revealed particle size distribution ranges from 8–288 nm for gold colloids and 15–297 nm for gold-PVP colloids. Gold-PVP nanostructured composites have shown an improvement in the antiviral activity against the H9N2 virus as compared to bare gold nanostructured particles.

Preparation of Metal Nitride Particles Using Arc Discharge in Liquid Nitrogen

A simple process to synthesize metal nitride particles was proposed using submerged arc discharge plasma in liquid nitrogen. Gibbs standard free energy was considered for the selection of the nitride-forming materials. In this study, titanium (Ti) and aluminum (Al) electrodes were used as raw materials for nitride particle preparation. Liquid nitrogen acted as a dielectric medium as well as a nitridation source in this process. A copper electrode was also used as a non-reactive material for comparison with the reactive Ti and Al electrodes. As the operating conditions of the experiments, the arc discharge current was varied from 5 A (low-power mode) to 30 A (high-power mode). The formation of titanium nitride (TiN) and aluminum nitride (AlN) was confirmed in the particles prepared in all experimental conditions by X-ray powder diffraction (XRD). The observation using a field emission scanning electron microscope (FE-SEM) and a field emission transmission electron microscope (FE-TEM) indicated that the synthesized TiN particles showed a cubic morphology, whereas AlN particles containing unreacted Al showed a spherical morphology. The experiments using different metal electrode configurations showed that the anode generated most of the particles in this process. Based on the obtained results, a particle formation mechanism was proposed.

Fructose-coated Ångstrom silver prevents sepsis by killing bacteria and attenuating bacterial toxin-induced injuries

Serious infection caused by multi-drug-resistant bacteria is a major threat to human health. Bacteria can invade the host tissue and produce various toxins to damage or kill host cells, which may induce life-threatening sepsis. Here, we aimed to explore whether fructose-coated Ångstrom-scale silver particles (F-AgÅPs), which were prepared by our self-developed evaporation-condensation system and optimized coating approach, could kill bacteria and sequester bacterial toxins to attenuate fatal bacterial infections.

Methods: A series of in vitro assays were conducted to test the anti-bacterial efficacy of F-AgÅPs, and to investigate whether F-AgÅPs could protect against multi-drug resistant Staphylococcus aureus (S. aureus)- and Escherichia coli (E. coli)-induced cell death, and suppress their toxins (S. aureus hemolysin and E. coli lipopolysaccharide)-induced cell injury or inflammation. The mouse models of cecal ligation and puncture (CLP)- or E. coli bloodstream infection-induced lethal sepsis were established to assess whether the intravenous administration of F-AgÅPs could decrease bacterial burden, inhibit inflammation, and improve the survival rates of mice. The levels of silver in urine and feces of mice were examined to evaluate the excretion of F-AgÅPs.

Results: F-AgÅPs efficiently killed various bacteria that can cause lethal infections and also competed with host cells to bind with S. aureus α-hemolysin, thus blocking its cytotoxic activity. F-AgÅPs inhibited E. coli lipopolysaccharide-induced endothelial injury and macrophage inflammation, but not by directly binding to lipopolysaccharide. F-AgÅPs potently reduced bacterial burden, reversed dysregulated inflammation, and enhanced survival in mice with CLP- or E. coli bloodstream infection-induced sepsis, either alone or combined with antibiotic therapy. After three times injections within 48 h, 79.18% of F-AgÅPs were excreted via feces at the end of the 14-day observation period.

Conclusion: This study suggests the prospect of F-AgÅPs as a promising intravenous agent for treating severe bacterial infections.

Microplasma assisted synthesis of silver nanoparticles capped with PVA, PVP and Sucrose

Silver nanoparticles (Ag NPs) have been synthesized by exposing Ar gas microplasma to liquid solution containing Ag+ ions. Sucrose, Polyvinyl Alcohol (PVA) and Polyvinylpyrrolidone (PVP) were added separately as capping agents in aqueous solution to avoid agglomeration of Ag NPs. There are two main mechanism involved in this experiment (1). interaction of electrons from microplasma with Ag+ ions present in aqueous solution and (2). Control of Ag NPs size by capping agents by surrounding Ag NPs. We have performed a comparison of capping performance of Sucrose and PVA in terms of stability of Ag NPs with the help of Ultraviolet-Visible spectroscopy (UV-vis). X-ray diffraction (XRD) analysis of Ag NPs capped with PVA and Sucrose shows average crystal size of 25 nm and 60 nm respectively. Dynamic Light Scattering (DLS) analysis was employed to measure the size distribution of Ag NPs capped with Sucrose, PVA and PVP capping agents. DLS showed that PVA-capped Ag NPs formed are more uniform in size as compared to Sucrose-capped. Average size of Ag NPs measured from DLS is 65 nm when capped with PVA and 120 nm when capped with Sucrose. Fourier Transform Infrared Spectroscopy (FTIR) spectrum obtained have bands of wavenumbers corresponding to functional groups of Sucrose and PVA which are present around Ag NPs.

Microplasma assisted synthesis of gold nanoparticle/graphene oxide nanocomposites and their potential application in SERS sensing

This is the first study on the deployment of direct current atmospheric pressure microplasma technique for the single step synthesis of gold nanoparticle/graphene oxide (AuNP/GO) nanocomposites. The nanocomposites were characterized using ultraviolet-visible spectroscopy (UV-vis), x-ray diffraction and x-ray photoelectron spectroscopy and their formation mechanisms have been discussed in detail. Our AuNP/GO nanocomposites are highly biocompatible and have demonstrated surface enhanced Raman scattering (SERS) properties as compared to pure AuNPs and pure GO. Their potential as SERS substrate has been further demonstrated using probe molecules (methylene blue) at different concentrations.

Atmospheric Pressure Plasma-Synthesized Gold Nanoparticle/Carbon Nanotube Hybrids for Photothermal Conversion

In this work, a room-temperature atmospheric pressure direct-current plasma has been deployed for the one-step synthesis of gold nanoparticle/carboxyl group-functionalized carbon nanotube (AuNP/CNT-COOH) nanohybrids in aqueous solution for the first time. Uniformly distributed AuNPs are formed on the surface of CNT-COOH, without the use of reducing agents or surfactants. The size of the AuNP can be tuned by changing the gold salt precursor concentration. UV-vis, ζ-potential, and X-ray photoelectron spectroscopy suggest that carboxyl surface functional groups on CNTs served as nucleation and growth sites for AuNPs and the multiple potential reaction pathways induced by the plasma chemistry have been elucidated in detail. The nanohybrids exhibit significantly enhanced Raman scattering and photothermal conversion efficiency that are essential for potential multimodal cancer treatment applications.

Synthesis of Ag/TiO2 nanocomposite via plasma liquid interactions: Improved performance as photoanode in dye-sensitized solar cell

Ag/TiO₂ nanocomposite was prepared by the atmospheric direct current plasma in aqueous solution to improve its performance in dye-sensitized solar cells (DSSCs) as the photoanode. The fabricated DSSC shows high power conversion efficiency over 6.5% and displays better long-term stability than that of referenced pure TiO₂. The comparison of photoluminescence spectra of Ag/TiO₂ and pure TiO₂ showed that only the Ag containing samples had notable photocurrent under visible light, which was attributed to the highly dispersed Ag, according to the EDS and XRD measurements. The short-circuit current density (Jsc) and open-circuit voltage (Voc) reached 13.43 mA cm^-2 and 0.72 V in Ag/TiO₂, and 9.44 mA cm^-2 and 0.68 V in pure TiO₂, respectively. The performance improvement in Ag/TiO₂ DSSC may occur due to the declined band-gap energy, retarded charge recombination and greater surface coverage of the sensitizing dye over Ag/TiO₂ nanocomposite.

Synthesis of metallic nanoparticles by microplasma

The synthesis of metallic nanoparticles has been of long standing interest, primarily induced by their novel and unique properties that differ considerably from bulk materials. Despite various methods have been developed, it is still a challenge to produce high-quality metallic nanoparticles with controllable properties in a simple, cost-effective and environmentally benign manner. However, the development of the microplasma-assisted technology can bring an answer to this formidable challenge. In the present work, four main microplasma configurations used for metallic synthesis of metallic nanoparticles are reviewed.  These are  hollow-electrode microdischarges, microplasma jets with external electrodes, microplasma jets with consumable electrodes and plasma–liquid systems. The state of the art characterization methodologies and diagnostic techniques for in situ microplasma-assisted precursor dissociation as well as ex situ metallic nanoparticles analysis is also summarized. Further, a broad category of representative examples of microplasma-induced metallic nanoparticle fabrication is presented, together with the discussion of possible synthesis mechanisms. This is followed by a brief introduction to related safety considerations. Finally, the future perspectives, associated challenges and feasible solutions for scale-up of this technique are pointed out.

Graphical Abstract:

Pulse-Modulated Radio-Frequency Alternating-Current-Driven Atmospheric-Pressure Glow Discharge for Continuous-Flow Synthesis of Silver Nanoparticles and Evaluation of Their Cytotoxicity toward Human Melanoma Cells

An innovative and environmentally friendly method for the synthesis of size-controlled silver nanoparticles (AgNPs) is presented. Pectin-stabilized AgNPs were synthesized in a plasma-reaction system in which pulse-modulated radio-frequency atmospheric-pressure glow discharge (pm-rf-APGD) was operated in contact with a flowing liquid electrode. The use of pm-rf-APGD allows for better control of the size of AgNPs and their stability and monodispersity. AgNPs synthesized under defined operating conditions exhibited average sizes of 41.62 ± 12.08 nm and 10.38 ± 4.56 nm, as determined by dynamic light scattering and transmission electron microscopy (TEM), respectively. Energy-dispersive X-ray spectroscopy (EDS) confirmed that the nanoparticles were composed of metallic Ag. Furthermore, the ξ-potential of the AgNPs was shown to be -43.11 ± 0.96 mV, which will facilitate their application in biological systems. Between 70% and 90% of the cancerous cells of the human melanoma Hs 294T cell line underwent necrosis following treatment with the synthesized AgNPs. Furthermore, optical emission spectrometry (OES) identified reactive species, such as NO, NH, N₂, O, and H, as pm-rf-APGD produced compounds that may be involved in the reduction of the Ag(I) ions.

In-liquid plasma: a novel tool in the fabrication of nanomaterials and in the treatment of wastewaters

Attempts to generate plasma in liquids have been successful and various devices have been proposed.

Stabilizer-free silver nanoparticles as efficient catalysts for electrochemical reduction of oxygen

In this work we demonstrated the potential of the He+5% H₂+1% N₂ plasma jet treatment for the synthesis of surfactant-free silver nanoparticles (Ag NPs) with narrow size distribution. The obtained colloidal solutions of electrostatically stabilized Ag NPs do not show any agglomeration for several months. Apart from an atomic thin oxide layer and the relatively weakly bound OH^- ions, the surface of Ag NPs can be considered as stabilizer-free. The surface charge (characterized by the zeta potential) of Ag NPs in solution was measured by electrophoretic light scattering technique. Plasmonic band position and width in the UV/VIS extinction spectra was utilized for the assessment of Ag NPs size distribution. Highly concentrated Ag NPs were uniformly deposited on the surface of the glassy carbon (GC) electrodes by vacuum-drying technique. The deposition process was monitored with a digital camera attached to a microscope. The assemblies of Ag NPs on the electrode surface were characterized by scanning electron microscopy. The Ag NP/GC catalysts were electrochemically tested in alkaline solution using the rotating disk electrode method. The Ag NP/GC electrodes exhibited high electrocatalytic activity toward the oxygen reduction reaction (ORR) in 0.1M KOH solution, indicating their potential applicability as cathode materials for alkaline fuel cells.

Size-controlled synthesis of gold nanoparticles by a novel atmospheric pressure glow discharge system with a metallic pin electrode and a flowing liquid electrode

A direct current atmospheric pressure glow discharge operated between a pin-type solid metallic electrode and the surface of a flowing solution, positively or negatively charged and serving as the flowing liquid anode or cathode, was used for synthesizing gold nanoparticles.

Plasma enhanced vortex fluidic device manipulation of graphene oxide

A vortex fluid device (VFD) with non-thermal plasma liquid processing within dynamic thin films has been developed.

Sustainable Life Cycles of Natural-Precursor-Derived Nanocarbons

Sustainable societal and economic development relies on novel nanotechnologies that offer maximum efficiency at minimal environmental cost. Yet, it is very challenging to apply green chemistry approaches across the entire life cycle of nanotech products, from design and nanomaterial synthesis to utilization and disposal. Recently, novel, efficient methods based on nonequilibrium reactive plasma chemistries that minimize the process steps and dramatically reduce the use of expensive and hazardous reagents have been applied to low-cost natural and waste sources to produce value-added nanomaterials with a wide range of applications. This review discusses the distinctive effects of nonequilibrium reactive chemistries and how these effects can aid and advance the integration of sustainable chemistry into each stage of nanotech product life. Examples of the use of enabling plasma-based technologies in sustainable production and degradation of nanotech products are discussed-from selection of precursors derived from natural resources and their conversion into functional building units, to methods for green synthesis of useful naturally degradable carbon-based nanomaterials, to device operation and eventual disintegration into naturally degradable yet potentially reusable byproducts.

Microplasma-assisted rapid synthesis of luminescent nitrogen-doped carbon dots and their application in pH sensing and uranium detection

Developing a simple synthesis method and expanding the application of carbon dots have attracted increasing attention. In this report, we have developed a facile method to synthesize fluorescent carbon dots (CDs) with the assistance of atmospheric-pressure microplasma. The CDs could be produced within a few minutes with no need of high temperature, external energy input, and multistep procedures. The as-prepared CDs had a relatively uniform size of approximately 2.3 nm. The FTIR spectrum and the XPS analysis showed that carbonyl groups and amide groups exist on the surface of CDs. The CDs showed bright blue luminescence and high stability in high salt concentration and low pH without further modification. A pH-dependent PL behavior was observed and could be applied for pH sensing in the range of 3-14. Moreover, the CDs could be utilized as a reagent capable of detecting U(vi) with a low detection limit and high selectivity.

Microplasma-chemical synthesis and tunable real-time plasmonic responses of alloyed AuxAg1−x nanoparticles

A new conceptual microplasma-based approach is developed to produce AuAg alloyed crystalline nanoparticles at atmospheric pressure and low temperatures, in the absence of a chemical reducing agent. Real-time plasmonic monitoring is demonstrated.