Zinc Oxide Spherical-Shaped Nanostructures: Investigation of Surface Reactivity and Interactions with Microbial and Mammalian Cells

Synergistic bactericidal combinations between gentamicin and chitosan capped ZnO nanoparticles: A promising strategy for repositioning this first-line antibiotic

Gentamicin (GEN), a widely used broad-spectrum antibiotic, faces challenges amid the global emergency of antimicrobial resistance. This study aimed to explore the synergistic effects of zinc oxide nanoparticles (ZnO NPs) in combination with GEN on the bactericidal activity against various bacterial strains. Results showed ZnO NPs with MICs ranging from 0.002 to 1.5 μg/mL, while the precursor salt displayed a MIC range of 48.75-1560 μg/mL. Chitosan (CS)-capped ZnO NPs exhibited even lower MICs than their uncapped counterparts, with the CS-capped synthesized ZnO NPs demonstrating the lowest values. Minimal bactericidal concentrations (MBC) aligned with MIC trends. Combinations of CS-capped synthesized ZnO NPs and GEN proved highly effective, inhibiting bacterial growth at significantly lower concentrations than GEN or ZnO NPs alone. This phenomenon may be attributed to the conformation of CS on the ZnO NPs' surface, enhancing the positive particle surface charge. This possibly facilitates a more effective interaction between ZnO NPs and microorganisms, leading to increased accumulation of zinc and GEN within bacterial cells and an overproduction of reactive oxygen species (ROS). It's crucial to note that, while this study did not specifically involve resistant strains, its primary focus remains on enhancing the overall antimicrobial activity of gentamicin. The research aims to contribute to addressing the global challenge of antimicrobial resistance, recognizing the urgent need for effective strategies to combat this critical issue. The findings, particularly the observed synergy between ZnO NPs and GEN, hold significant implications for repositioning the first-line antibiotic GEN.

Deciphering the role of water and a zinc-doping process in a polyol-based approach for obtaining Zn/Co/Al-based spinels: toward "green" mesoporous inorganic pigments

Two new families of zinc/cobalt/aluminum-based pigments, with a unique composition, were obtained through the polyol method. The hydrolysis process of a mixture of Co(CH3COO)2, Zn(acac)2 and Al(acac)3 (acac- = acetylacetonate ion) in 1,4-butanediol afforded dark blue gels (wPZnxCo1-xAl), in the presence of a supplementary amount of water, and light green powders (PZnxCo1-xAl), respectively, for the water-free procedure (x = 0, 0.2, 0.4). The calcination of the precursors yielded dark green (wZnxCo1-xAl) and blue (ZnxCo1-xAl) products. XRD measurements and Rietveld refinement indicate the co-existence of three spinel phases, in different proportions: ZnxCo1-xAl2O4, Co3O4 and the defect spinel, γ-Al2.67O4. The Raman scattering and XPS spectra are in agreement with the compositions of the samples. The morphology of wZnxCo1-xAl consists of large and irregular spherical particle aggregates (ca. 5-100 mm). Smaller agglomerates (ca. 1-5 mm) with a unique silkworm cocoon-like hierarchical morphology composed of cobalt aluminate cores covered with flake-like alumina shells are formed for ZnxCo1-xAl. TEM and HR-TEM analyses revealed the formation of crystalline, polyhedral particles of 7-43 nm sizes for wZnxCo1-xAl, while for ZnxCo1-xAl, a duplex-type morphology, with small (7-13 nm) and larger (30-40 nm) particles, was found. BET assessment showed that both series of oxides are mesoporous materials, with different pore structures, with the water-free samples exhibiting the largest surface areas due, most likely, to the high percent of aluminum oxide. A chemical mechanism is proposed to highlight the role of the water amount and the nature of the starting compounds in the hydrolysis reaction products and, further, in the morpho-structural features and composition of the resulting spinel oxides. The CIE L*a*b* and C* colorimetric parameters indicate that the pigments are bright, with a moderate degree of luminosity, presenting an outstanding high blueness.

Copper(II) Oxide Nanoparticles Embedded within a PEDOT Matrix for Hydrogen Peroxide Electrochemical Sensing

The aim of this study is the preparation of nanostructured copper(II) oxide-based materials (CuONPs) through a facile additive-free polyol procedure that consists of the hydrolysis of copper(II) acetate in 1,4-butane diol and its application in hydrogen peroxide sensing. The nonenzymatic electrochemical sensor for hydrogen peroxide determination was constructed by drop casting the CuONP sensing material on top of a glassy carbon electrode (GCE) modified by a layer of poly(3,4-ethylenedioxythiophene) conducting polymer (PEDOT). The PEDOT layer was prepared on GCE using the sinusoidal voltage method. The XRD pattern of the CuONPs reveals the formation of the monoclinic tenorite phase, CuO, with average crystallite sizes of 8.7 nm, while the estimated band gap from UV-vis spectroscopy is of 1.2 eV. The SEM, STEM, and BET analyses show the formation of quasi-prismatic microaggregates of nanoparticles, with dimensions ranging from 1 µm up to ca. 200 µm, with a mesoporous structure. The developed electrochemical sensor exhibited a linear response toward H₂O₂ in the concentration range from 0.04 to 10 mM, with a low detection limit of 8.5 μM of H₂O₂. Furthermore, the obtained sensor possessed an excellent anti-interference capability in H₂O₂ determination in the presence of interfering compounds such as KNO₃ and KNO₂.

Zinc Oxide Synthesis from Extreme Ratios of Zinc Acetate and Zinc Nitrate: Synergistic Morphology

The synthesis of ZnO comprising different ratios of zinc acetate (ZA) and zinc nitrate (ZN) from the respective zinc precursor solutions was successfully completed via a simple precipitation method. Zinc oxide powders with different mole ratios of ZA/ZN were produced—80/1, 40/1, and 20/1. The crystallinity, microstructure, and optical properties of all produced ZnO powders were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-Vis-NIR spectrophotometry. The average agglomerated particle sizes of ZnO-80/1, ZnO-40/1, and ZnO-20/1 were measured at 655, 640, and 620 nm, respectively, using dynamic light scattering (DLS). The optical properties of ZnO were significantly affected by the extreme ratio differences in the zinc precursors. ZnO-80/1 was found to have a unique coral-sheet structure morphology, which resulted in its superior ability to reflect near-infrared (NIR) radiation compared to ZnO-40/1 and ZnO-20/1. The NIR-shielding performances of ZnO were assessed using a thermal insulation test, where coating with ZnO-80/1 could lower the inner temperature by 5.2 °C compared with the neat glass substrate. Due to the synergistic effects on morphology, ZnO-80/1 exhibited the property of enhanced NIR shielding in curtailing the internal building temperature, which allows for its utilization as an NIR-reflective pigment coating in the construction of building envelopes.

Mechanical and Water Absorption Properties of Short Banana Fiber/Unsaturated Polyester/Molecular Sieves + ZnO Nanorod Hybrid Nanobiocomposites

ZnO nanorods were prepared by the sol-gel method and characterized using UV-visible absorption spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, powder X-ray diffraction (PXRD), thermogravimetric analysis/differential thermogravimetry (TGA/DTG), high-resolution transmission electron microscopy (HR-TEM), field emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray spectroscopy (EDAX). Banana fiber/polyester resin (BF/PE) biocomposites and BF/PE/MS/nano ZnO nanobiocomposites were made using the untreated and chemically treated (with NaOH, formic acid, acetic anhydride, hydrogen peroxide, and potassium permanganate) banana fiber (BF), unsaturated polyester resin (PE), molecular sieves (MS), and the prepared ZnO nanorods. The KMnO₄, Ac₂O, and NaOH treatments enhanced the thermal stability of the nanobiocomposites. Addition of 2% of ZnO nanorods increased the tensile strength of all of the chemically treated BF/PE/MS biocomposites. The chemical treatments alone decreased (NaOH-15.4 MPa; KMnO₄-14.5 MPa; H₂O₂-9.9 MPa; Ac₂O-7.9 MPa; HCOOH-6.9 MPa) the compressive strength of the untreated BF/PE/MS biocomposite (25.9 MPa). But the chemical treatment and addition of ZnO nanorods enhanced the compressive strength effectively (48.5, 41.6, 39.4, 37.0, and 34.6 MPa for NaOH, HCOOH, KMnO₄, H₂O₂, and Ac₂O treatments, respectively) compared to the untreated BF/PE/MS biocomposites (24.0 MPa). The H₂O₂ (69.0 MPa) and NaOH (62.9 MPa) treatments enhanced the flexural strength of the untreated BF/PE biocomposites (51.6 MPa). The addition of ZnO nanorods enhanced the flexural strength of all of the chemically treated (except NaOH) BF/PE/MS biocomposites (55.7, 59.4, 79.0, and 67.4 MPa for HCOOH, Ac₂O, H₂O₂, and KMnO₄ treatments, respectively). The impact strengths of the biocomposites were enhanced by both chemical treatments and addition of ZnO nanorods. The addition of ZnO nanorods decreased the water absorption of the biocomposites significantly from 24.3% for the untreated to a minimum of 14.5% for the H₂O₂-treated BF/PE/MS/ZnO nanobiocomposite.

Modulation of Quorum Sensing and Biofilms in Less Investigated Gram-Negative ESKAPE Pathogens

Pathogenic bacteria have the ability to sense their versatile environment and adapt by behavioral changes both to the external reservoirs and the infected host, which, in response to microbial colonization, mobilizes equally sophisticated anti-infectious strategies. One of the most important adaptive processes is the ability of pathogenic bacteria to turn from the free, floating, or planktonic state to the adherent one and to develop biofilms on alive and inert substrata; this social lifestyle, based on very complex communication networks, namely, the quorum sensing (QS) and response system, confers them an increased phenotypic or behavioral resistance to different stress factors, including host defense mechanisms and antibiotics. As a consequence, biofilm infections can be difficult to diagnose and treat, requiring complex multidrug therapeutic regimens, which often fail to resolve the infection. One of the most promising avenues for discovering novel and efficient antibiofilm strategies is targeting individual cells and their QS mechanisms. A huge amount of data related to the inhibition of QS and biofilm formation in pathogenic bacteria have been obtained using the well-established gram-positive Staphylococcus aureus and gram-negative Pseudomonas aeruginosa models. The purpose of this paper was to revise the progress on the development of antibiofilm and anti-QS strategies in the less investigated gram-negative ESKAPE pathogens Klebsiella pneumoniae, Acinetobacter baumannii, and Enterobacter sp. and identify promising leads for the therapeutic management of these clinically significant and highly resistant opportunistic pathogens.

ZnO encapsulants: Design and new view

ZnO encapsulants with capsular configurations (e.g. a large inner cavity, sizeable pore, low density and high specific surface area) have attracted considerable attention as effective and promising candidates in various fields owing to the merits of ZnO (e.g. UV protection, photoelectric catalysis, gas sensitivity, antibacterial effect). However, the research on ZnO encapsulants has not yet reached the eruptive stage. This probably due to their high morphological flexibility and relatively low structural strength that is not easy to control during the preparation process. In this review, the principles of cavity-generating and pore-forming are firstly discussed in depth after going through the synthesis of hollow ZnO in the past ten years. Moreover, the regulation of cavity diameter and pore size of different synthetic strategies is investigated. Then, the research progress of ZnO encapsulants is debated in detail from the loading and release of functional materials and the corresponding characterization. Finally, some potential designs and new views on the future research and development of ZnO encapsulants are concluded.

Growth and formation mechanism of shape-selective preparation of ZnO structures: correlation of structural, vibrational and optical properties

A shape-selective preparation method was used to obtain highly crystalline rod-, needle-, nut-, and doughnut-like ZnO morphologies with distinct particle sizes and surface areas.

Zinc oxide‑selenium heterojunction composite: Synthesis, characterization and photo-induced antibacterial activity under visible light irradiation

The designing of new antibacterial agents with high and long-lasting activities are urgently needed in order to cope with the fast-emerging bacterial resistance. Zinc oxide nanoparticles (ZnO) have shown a significant promise as broad-spectrum antibacterial agents, and are efficient material in compromising bacterial membrane stability that leads to an increased cell permeability to nano-products. However, further engineering is required to improve their biological activities and to minimize their toxicity to healthy cells. In an attempt to resolve this issue, two semiconductor materials, ZnO and selenium (Se), were fabricated into a unique structural composite by a newly developed facile green method, and the designed composite was applied as an antibacterial nanomedicine. The developed methodology involves the initial preparation of ZnO, followed by its fabrication with Se at different temperatures (70 °C to 95 °C). Our experimental data showed that well defined interpenetrated crystalline Se network on ZnO (ZnO-Se) can be obtained at 80 °C for 180 min. The as-prepared ZnO-Se showed promising results in inhibiting the challenged bacterial strains under light irradiation (visible light) as compared to free ZnO. The enhanced biocidal property of ZnO-Se could be ascribed to its improved light-harvesting ability for sustainable induction of reactive oxygen species (ROS) and an active contact killing mechanism. Thus, ZnO-Se composite with a novel architecture could be a promising material in the treatment of bacterial infections by a mutual antibacterial synergy from the incorporated elements. Interestingly, the ZnO-Se has the ability to scavenge the overproduction of hydroxyl radicals, thus protecting the healthy cells from oxidative damage.

Self-assembled zinc oxide hierarchical structures with enhanced antibacterial properties from stacked chain-like zinc oxalate compounds

Single ZnO crystallites assembled into porous hierarchical structures have been prepared by topotactic thermal decomposition of in situ obtained zinc oxalate precursors, whose synthesis involves a redox reaction between 1,2-ethanediol and nitrate ion. For the first time it was demonstrated that post-synthesis protocols of the precursors (e.g. ultrasound irradiation, hydrolytic decomposition) master the hydrogen bonds formed between oxalate chains, allowing that way the adjustment of materials properties (morphology, porosity and optical) and a rational introduction of different dopants (Eu³⁺/Er³⁺). The ZnO surface reactivity is confirmed by the significant biocidal activity of the obtained materials against Gram-positive and Gram-negative planktonic and biofilm-embedded cells, superior to those reported in the literature for other ZnO-based materials or antibiotics, associated also with a good biocompatibility.