Zinc nanostructures for oxygen scavenging

Effects of Zn-ZnO Core-Shell Nanoparticles on Antimicrobial Mechanisms and Immune Cell Activation

The deposition of zinc-zinc oxide nanoparticles (Zn-ZnO NPs) onto porous Ta2O5 surfaces enriched with calcium phosphate by DC magnetron sputtering was investigated to improve the surface antimicrobial activity without triggering an inflammatory response. Different sizes and amounts of Zn NPs obtained by two optimized different depositions and an additional thin carbon (C) layer deposited over the NPs were explored. The deposition of the Zn NPs and the C layer mitigates the surface porosity, increasing the surface hydrophobicity and decreasing the surface roughness. The possible antimicrobial effect and immune system activation of Zn-ZnO NPs were investigated in Candida albicans and macrophage cells, respectively. It was found that the developed surfaces displayed a fungistatic behavior, as they impair the growth of C. albicans between 5 and 24 h of culture. This behavior was more evident on the surfaces with bigger NPs and the highest amounts of Zn. The same trend was observed in both reactive oxygen species (ROS) generation and loss of C. albicans' membrane integrity. After 24 h of culture, cell toxicity was also dependent on the amount of the NPs. Cell toxicity was observed in surfaces with the highest amount of Zn NPs and with the C layer, while cells were able to grow without any signs of cytotoxicity in the porous surfaces with the lowest amount of NPs. The same Zn-dose-dependent behavior was noticed in the TNF-α production. The Zn-containing surfaces show a vastly inferior cytokine secretion than the lipopolysaccharide (LPS)-stimulated cells, indicating that the modified surfaces do not induce an inflammatory response from macrophage cells. This study provides insights for understanding the Zn amount threshold that allows a simultaneous inhibition of the fungi growth with no toxic effect and the main antimicrobial mechanisms of Zn-ZnO NPs, contributing to future clinical applications.

Effect of nanopackaging on the quality of edible mushrooms and its action mechanism: A review

With higher demands for food packaging and the development of nanotechnology, nanopackaging is becoming a research hotspot in the field of food packaging because of its superb preservation effect, and it can effectively resist oxidation and regulates energy metabolism to maintain the quality and prolong the shelf life of mushrooms. Furthermore, under the background of SARS-CoV-2 pandemic, nanomaterials could be a potential tool to prevent virus transmission because of their excellent antiviral activities. However, the investigation and application of nanopackaging are facing many challenges including costs, environmental pollution, poor in-depth genetic research for mechanisms and so on. This article reviews the preservation effect and mechanisms of nanopackaging on the quality of mushrooms and discusses the trends and challenges of using these materials in food packaging technologies with the focus on nanotechnology and based on recent studies.

Development and Characterization of Electrospun Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Biopapers Containing Cerium Oxide Nanoparticles for Active Food Packaging Applications

Food quality is mainly affected by oxygen through oxidative reactions and the proliferation of microorganisms, generating changes in its taste, odor, and color. The work presented here describes the generation and further characterization of films with active oxygen scavenging properties made of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) loaded with cerium oxide nanoparticles (CeO₂NPs) obtained by electrospinning coupled to a subsequent annealing process, which could be used as coating or interlayer in a multilayer concept for food packaging applications. The aim of this work is to explore the capacities of these novel biopolymeric composites in terms of O₂ scavenging capacity, as well as antioxidant, antimicrobial, barrier, thermal, and mechanical properties. To obtain such biopapers, different ratios of CeO₂NPs were incorporated into a PHBV solution with hexadecyltrimethylammonium bromide (CTAB) as a surfactant. The produced films were analyzed in terms of antioxidant, thermal, antioxidant, antimicrobial, optical, morphological and barrier properties, and oxygen scavenging activity. According to the results, the nanofiller showed some reduction of the thermal stability of the biopolyester but exhibited antimicrobial and antioxidant properties. In terms of passive barrier properties, the CeO₂NPs decreased the permeability to water vapor but increased the limonene and oxygen permeability of the biopolymer matrix slightly. Nevertheless, the oxygen scavenging activity of the nanocomposites showed significant results and improved further by incorporating the surfactant CTAB. The PHBV nanocomposite biopapers developed in this study appear as very interesting constituents for the potential design of new active organic recyclable packaging materials.

Oxygen Adsorption on Polar and Non-Polar Zn:ZnO Heterostructures from First Principles

Zn:ZnO nanostructures have been studied extensively due to their potential use in many applications, such as oxygen scavengers for food packaging applications. Under atmospheric conditions, ZnO grows on the surface of Zn via an oxidation process. The mechanisms governing Zn oxidation are still not fully understood, with classical oxidation models, such as the Cabrera Mott, underestimating the oxide thickness of Zn:ZnO core-shell structures. In this work, Ab initio DFT calculations were performed to assess the adsorption properties of oxygen molecules on Zn:ZnO heterostructures to help elucidate the mechanisms involved in the growth of a ZnO film on a Zn substrate. Results suggest that the charge transfer mechanism from the Zn:ZnO heterostructures to the adsorbed oxygen layer can be promoted by two different processes: the electronic doping of ZnO due to the formation of the Zn:ZnO interface and the excess surface charge due to the presence of dangling bonds on the as cleaved ZnO.

Zn and Zn-Fe Nanostructures with Multifunctional Properties as Components for Food Packaging Materials

Metallic and bimetallic nanostructures have shown interesting chromatic and antibacterial properties, and they can be used in various applications. In this work, zinc (Zn) and iron (Fe) nanostructures were produced with different morphologies: (i) pure Zn; (ii) Zn-Fe nanoalloys; (iii) Zn-Fe nanolayers (Zn-Fe NLs); and (iv) Zn nanolayers combined with Fe nanoparticles (Zn NLs + Fe NPs). The aim was to produce components for food packaging materials with active and intelligent properties, including oxygen absorption capacity, chromatic properties, and antibacterial properties. Thus, the morphology, structure, and chemical composition of the samples were characterized and correlated with their oxidation, chromatic, and antibacterial properties. The results revealed a relevant reduction in the coating’s opacity after oxidation varying from 100 to 10% depending on the morphology of the system. All coatings exhibited significant antibacterial activity against S. aureus, revealing a direct correlation with Zn content. The incorporation of Fe for all atomic arrangements showed a negative impact on the antibacterial effect against E. coli, decreasing to less than half the zone of inhibition for Zn-Fe NLs and Zn NLs + Fe NPs and suppressing the antibacterial effect for Zn-Fe alloy when compared with the pure Zn system.

Porous tantalum oxide with osteoconductive elements and antibacterial core-shell nanoparticles: A new generation of materials for dental implants

Implant surfaces with cytocompatible and antibacterial properties are extremely desirable for the prevention of implant's infection and the promotion of osseointegration. In this work, both micro-arc oxidation (MAO) and DC magnetron sputtering techniques were combined in order to endow tantalum-based surfaces with osteoblastic cytocompatibility and antibacterial activity. Porous Ta₂O₅ layers containing calcium (Ca) and phosphorous (P) were produced by MAO (TaCaP) to mimic the bone tissue morphology and chemical composition (Ca/P ratio close to 1.67). Furthermore, zinc (Zn) nanoparticles were deposited onto the previous surfaces by DC magnetron sputtering without or with an additional thin carbon layer deposited over the nanoparticles (respectively, TaCaP-Zn and TaCaP-ZnC) to control the Zn ions (Zn²⁺) release. Before osteoblastic cell seeding, the surfaces were leached for three time-points in PBS. All modified samples were cytocompatible. TaCaP-Zn slightly impaired cell adhesion but this was improved in the samples leached for longer immersion times. The initial cell adhesion was clearly improved by the deposition of the carbon layer on the Zn nanoparticles, which also translated to a higher proliferation rate. Both Zn-containing surfaces presented antibacterial activity against S. aureus. The two surfaces were active against planktonic bacteria, and TaCaP-Zn also inhibited sessile bacteria. Attributing to the excellent in vitro performance of the nanostructured Ta surface, with osteoconductive elements by MAO followed by antimicrobial nanoparticles incorporation by magnetron sputtering, this work is clearly a progress on the strategy to develop a new generation of dental implants.

Decomposition of Bis(acetylacetonate)zinc(II) by Slow Electrons

The production of zinc-containing nanostructures has a large variety of applications. Using electron beam techniques to degrade organometallic molecules for that purpose is perhaps one of the most versatile methods. In this work, we investigate the scattering of low-energy (<12 eV) electrons with bis(acetylacetonate)zinc(II) molecules. We show that core excited and high-lying shape resonances are mainly responsible for the production of the precursor anions as well as the ligand negative fragments, which are observed exclusively at electron energies of >3 eV. The mechanisms for electron capture and then molecular dissociation are discussed in terms of density functional theory studies.

Plasmonic Ag nanoparticles embedded in lithium tantalate crystal for ultrafast laser generation

We report the Ag nanoparticles (NPs) embedded in LiTaO₃ (AgNP:LT) by direct Ag⁺ ion implantation. Transmission electron microscope imaging indicates that the embedded Ag NPs have an average diameter of 3.65 nm. The linear optical absorption spectrum of AgNP:LT peaking at 477 nm is observed owing to the typical effect of localized surface plasmon resonance. Z-scan investigation shows ultrafast saturable absorption of AgNP:LT at the near infrared 1 μm wavelength, which enables AgNP:LT to be a new saturable absorber (SA) for the generation of 1 μm Q-switched mode-locked pulsed laser with pulse duration of 35 ps and repetition rate of 8.74 GHz. This work not only opens a new way to tailor the nonlinearity of LiTaO₃ by embedding Ag⁺ NPs, but also develops AgNP:LT as a new SA for ultrafast laser generation.

Recent Developments in Food Packaging Based on Nanomaterials

The increasing demand for high food quality and safety, and concerns of environment sustainable development have been encouraging researchers in the food industry to exploit the robust and green biodegradable nanocomposites, which provide new opportunities and challenges for the development of nanomaterials in the food industry. This review paper aims at summarizing the recent three years of research findings on the new development of nanomaterials for food packaging. Two categories of nanomaterials (i.e., inorganic and organic) are included. The synthetic methods, physical and chemical properties, biological activity, and applications in food systems and safety assessments of each nanomaterial are presented. This review also highlights the possible mechanisms of antimicrobial activity against bacteria of certain active nanomaterials and their health concerns. It concludes with an outlook of the nanomaterials functionalized in food packaging.

Lattice induced crystallization of nanodroplets: the role of finite-size effects and substrate properties in controlling polymorphism

Targeting specific technological applications requires the control of nanoparticle properties, especially the crystalline polymorph. Freezing a nanodroplet deposited on a solid substrate leads to the formation of crystalline structures. We study the inherent mechanisms underlying this general phenomenon by means of molecular dynamics simulations. Our work shows that different crystal structures can be selected by finely tuning the solid substrate lattice parameter. Indeed, while for our system, face-centered cubic is usually the most preponderant structure, the growth of two distinct polymorphs, hexagonal centered packing and body-centered cubic, was also observed even when the solid substrate was face-centered cubic. Finally, we also demonstrated that the growth of hexagonal centered packing is conditioned by the appearance of large enough body-centered cubic clusters thus suggesting the presence of a cross-nucleation pathway. Our results provide insights into the impact of nanoscale effects and solid substrate properties towards the growth of polymorphic nanomaterials.

Gradient in defect density of ZnO nanorods grown by cathodic delamination, a corrosion process, leads to end-specific luminescence

ZnO nanorods were grown on a zinc substrate via cathodic delamination of a polymer coating, a tailored corrosion process, at room temperature. A comparison between in situ Raman spectra and post mortem cross sectional analysis by Raman spectroscopy, photoluminescence spectroscopy and scanning electron microscopy shows that in the initial stages of the synthesis, preferentially defect rich ZnO grows. At later stages, crystalline wurtzite ZnO growth dominates. The result is nanorod arrays consisting of nanorods with a large density of point defects in the ≈500 nm range near the zinc substrate, and low defect density in the regions further away from the interface. The growth, which proceeds over several hours, can be interrupted at any time. Large salt concentrations in the corrosive medium increase the growth rate, but also the amount of point defects. The resulting rods show strongly position-dependent luminescence and Raman spectra. Different luminescence can thus be selectively excited, based on the position of excitation.