Morphology-directed synthesis of ZnO nanostructures and their antibacterial activity

Catharanthus roseus-assisted bio-fabricated zinc oxide nanoparticles for promising antibacterial potential against Klebsiella pneumoniae

This study emphasized on the synthesis of zinc oxide nanoparticles (ZnO NPs) in an environmentally friendly manner from the extract of Catharanthus roseus leaves and its antibacterial assessment against the pneumonia-causing pathogen Klebsiella pneumoniae. This simple and convenient phytosynthesis approach is found to be beneficial over conventional methods, wherein plants serve as excellent reducing, capping, and stabilizing agents that enables the formation of ZnO NPs without the use of harmful chemicals. The formation of ZnO NPs was confirmed through several characterization techniques such as UV-visible spectroscopy, XRD, FT-IR, SEM, HR-TEM, and EDX. XRD analysis revealed high polycrystallinity with crystallite size of approximately 13 nm. SEM and HR-TEM revealed the hexagonal structure of ZnO NPs with the particle size range of 20-50 nm. The EDX shows the elemental purity without any impurity. Furthermore, the antibacterial efficacy by the technique of disc diffusion exhibited clear inhibition zones in ZnO NPs-treated discs. In addition, 125 µg/mL of ZnO NP concentration showed minimum inhibition by the microbroth dilution method. The potent inhibitory activity was further validated with trypan blue dye exclusion and fluorescence microscopy. Finally, SEM examination confirmed the efficient antibacterial potential of ZnO NPs through disruption of the intact morphology of Klebsiella pneumoniae.

Sprayable, thermosensitive hydrogels for promoting wound healing based on hollow, porous and pH-sensitive ZnO microspheres

A solvothermal method and the subsequent heat treatment process were developed to fabricate hollow ZnO particles with hierarchical pores on a large scale. The as-obtained hollow, porous ZnO microspheres with tunable sizes, high specific surface areas, pH sensitivity, antibacterial properties, and high adsorption capacities showed significant advantages for drug delivery. Sprayable hydrogels containing hollow, porous ZnO microspheres and curcumin nanoparticles (CNPs) were prepared to accelerate wound healing. The water-dispersed CNPs promoted both the migration of fibroblasts and angiogenesis and an aqueous solution of Pluronic F127 (a temperature-sensitive phase-change hydrogel material) was shown to be an effective choice for medical dressings. The experimental data suggest that hollow, porous ZnO microspheres can be loaded with additional CNPs to achieve continuous long-term therapeutic effects.

Transforming Natural Eggshell and Diatomite into Bioactive Calcium Silicate Material for Bone Regeneration

Calcium silicate (CS), a new and important bioceramic bone graft material, is prepared by using eggshells, which have a porous structure and are rich in calcium ions. Furthermore, the preparation of new CS materials using eggshells and diatomaceous earth minimizes their negative impact on the environment. In this study, we prepared CS materials using a high-temperature calcination method. The composition of the material was demonstrated by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analysis. Scanning electron microscopy (SEM) analysis confirmed the porous structure of the CS material. We also introduced ZnO to prepare ZnO-CS with antibacterial properties and showed that ZnO-CS exhibits excellent antibacterial effects through in vitro antibacterial experiments. Subsequent in vitro mineralization experiments demonstrated that ZnO-CS promoted the formation of a hydroxyapatite layer. Furthermore, in vitro cytotoxicity experiments demonstrated that ZnO-CS had very good biosafety and promoted cell proliferation. These findings were confirmed through subsequent cell proliferation experiments. Our results indicate that the novel ZnO-CS is a promising candidate for bone tissue engineering.

In the View of Electrons Transfer and Energy Conversion: The Antimicrobial Activity and Cytotoxicity of Metal-Based Nanomaterials and Their Applications

The global pandemic and excessive use of antibiotics have raised concerns about environmental health, and efforts are being made to develop alternative bactericidal agents for disinfection. Metal-based nanomaterials and their derivatives have emerged as promising candidates for antibacterial agents due to their broad-spectrum antibacterial activity, environmental friendliness, and excellent biocompatibility. However, the reported antibacterial mechanisms of these materials are complex and lack a comprehensive understanding from a coherent perspective. To address this issue, a new perspective is proposed in this review to demonstrate the toxic mechanisms and antibacterial activities of metal-based nanomaterials in terms of energy conversion and electron transfer. First, the antimicrobial mechanisms of different metal-based nanomaterials are discussed, and advanced research progresses are summarized. Then, the biological intelligence applications of these materials, such as biomedical implants, stimuli-responsive electronic devices, and biological monitoring, are concluded based on trappable electrical signals from electron transfer. Finally, current improvement strategies, future challenges, and possible resolutions are outlined to provide new insights into understanding the antimicrobial behaviors of metal-based materials and offer valuable inspiration and instructional suggestions for building future intelligent environmental health.

Hydrophilic ZnO/C nanocomposites with superior adsorption, photocatalytic, and photo-enhanced antibacterial properties for synergistic water purification

Owing to the numerous potential applications of ZnO nanomaterials, the development of ZnO-based nanocomposites has become of great scientific interest in various fields. In this paper, we are reporting the fabrication of a series of ZnO/C nanocomposites through a simple "one-pot" calcination method under three different temperatures, 500 ℃, 600 ℃, and 700 ℃, with samples labeled as ZnO/C-500, -600, and -700, respectively. All samples exhibited adsorption capabilities and photon-activated catalytic and antibacterial properties, with the ZnO/C-700 sample showing superior performance among the three. The carbonaceous material in ZnO/C is key to expanding the optical absorption range and improving the charge separation efficiency of ZnO. The remarkable adsorption property of the ZnO/C-700 sample was demonstrated using Congo red dye, and is credited to its good hydrophilicity. It was also found to exhibit the most notable photocatalysis effect due to its high charge transfer efficiency. The hydrophilic ZnO/C-700 sample was also examined for antibacterial effects both in vitro (against Escherichia coli and Staphylococcus aureus) and in vivo (against MSRA-infected rat wound model), and it was observed to exhibit synergistic killing performance under visible-light irradiation. A possible cleaning mechanism is proposed on the basis of our experimental results. Overall, this work presents a facile way of synthesizing ZnO/C nanocomposites with outstanding adsorption, photocatalysis, and antibacterial properties for the efficient treatment of organic and bacterial contaminants in wastewater.

Antibacterial Effects of ZnO Nanodisks: Shape Effect of the Nanostructure on the Lethality in Escherichia coli

The role of the shape of the nanostructure on the antibacterial effects of ZnO nanodisks has been investigated by detailed mass spectrometry-based proteomics along with other spectroscopic and microscopic studies on E. coli. The primary interaction study of the E. coli cells in the presence of ZnO nanodisks showed rigorous cell surface damage disrupting the cell wall/membrane components detected by microscopic and ATR-FTIR studies. Protein profiling of whole-cell extracts in the presence and absence of ZnO nanodisks identified several proteins that are upregulated and downregulated under the stress of the nanodisks. This suggests that the bacterial response to the primary stress leads to a secondary impact of ZnO nanodisk toxicity via regulation of the expression of specific proteins. Results showed that the ZnO nanodisks lead to the over-expression of peptidyl-dipeptidase Dcp, Transketolase-1, etc., which are important to maintaining the osmotic balance in the cell. The abrupt change in osmotic pressure leads to mechanical injury to the membrane, and nutritional starvation conditions, which is revealed from the expression of the key proteins involved in membrane-protein assembly, maintaining membrane integrity, cell division processes, etc. Thus, indicating a deleterious effect of ZnO nanodisk on the protective layer of E. coli. ZnO nanodisks seem to primarily affect the protective membrane layer, inducing cell death via the development of osmotic shock conditions, as one of the possible reasons for cell death. These results unravel a unique behavior of the disk-shaped ZnO nanostructure in executing lethality in E. coli, which has not been reported for other known shapes or morphologies of ZnO nanoforms.

Microbial Mediated Synthesis of Zinc Oxide Nanoparticles, Characterization and Multifaceted Applications

Nanoparticles have gained considerable importance compared to bulk counterparts due to their unique properties. Due to their high surface to volume ratio and high reactivity, metallic and metal-oxide nanostructures have shown great potential applications. Among them, zinc oxide nanoparticles (ZnONPs) have gained tremendous attention attributed to their unique properties such as low toxicity, biocompatibility, simplicity, easy fabrication, and environmental friendly. Remarkably, ZnONPs exhibit optical, physical, antimicrobial, anticancer, anti-inflammatory and wound healing properties. These nanoparticles have been applied in various fields such as in biomedicine, biosensors, electronics, food, cosmetic industries, textile, agriculture and environment. The synthesis of ZnONPs can be performed by chemical, physical and biological methods. Although the chemical and physical methods suffer from some disadvantages such as the involvement of high temperature and pressure conditions, high cost and not environmentally friendly, the green synthesis of ZnONPs offers a promising substitute to these conventional methods. On that account, the microbial mediated synthesis of ZnONPs is clean, eco-friendly, nontoxic and biocompatible method. This paper reviews the microbial synthesis of ZnONPs, parameters used for the optimization process and their physicochemical properties. The potential applications of ZnONPs in biomedical, agricultural and environmental fields as well as their toxic aspects on human beings and animals have been reviewed.

The Study on Molecular Profile Changes of Pathogens via Zinc Nanocomposites Immobilization Approach

The most critical group of all includes multidrug resistant bacteria that pose a particular threat in hospitals, as they can cause severe and often deadly infections. Modern medicine still faces the difficult task of developing new agents for the effective control of bacterial-based diseases. The targeted administration of nanoparticles can enhance the efficiency of conventional pharmaceutical agents. However, the interpretation of interfaces' interactions between nanoparticles and biological systems still remains a challenge for researchers. In fact, the current research presents a strategy for using ZnO NPs immobilization with ampicillin and tetracycline. Firstly, the study provides the mechanism of the ampicillin and tetracycline binding on the surface of ZnO NPs. Secondly, it examines the effect of non-immobilized ZnO NPs, immobilized with ampicillin (ZnONPs/AMP) and tetracycline (ZnONPs/TET), on the cells' metabolism and morphology, based on the protein and lipid profiles. A sorption kinetics study showed that the antibiotics binding on the surface of ZnONPs depend on their structure. The efficiency of the process was definitely higher in the case of ampicillin. In addition, flow cytometry results showed that immobilized nanoparticles present a different mechanism of action. Moreover, according to the MALDI approach, the antibacterial activity mechanism of the investigated ZnO complexes is mainly based on the destruction of cell membrane integrity by lipids and proteins, which is necessary for proper cell function. Additionally, it was noticed that some of the identified changes indicate the activation of defense mechanisms by cells, leading to a decrease in the permeability of a cell's external barriers or the synthesis of repair proteins.

Enzymatically-degradable hydrogel coatings on titanium for bacterial infection inhibition and enhanced soft tissue compatibility via a self-adaptive strategy

Ideal percutaneous titanium implants request both antibacterial ability and soft tissue compatibility. ZnO structure constructed on titanium has been widely proved to be helpful to combat pathogen contamination, but the biosafety of ZnO is always questioned. How to maintain the remarkable antibacterial ability of ZnO and efficiently reduce the corresponding toxicity is still challenging. Herein, a hybrid hydrogel coating was constructed on the fabricated ZnO structure of titanium, and the coating was proved to be enzymatically-degradable when bacteria exist. Then the antibacterial activity of ZnO was presented. When under the normal condition (no bacteria), the hydrogel coating was stable and tightly adhered to titanium. The toxicity of ZnO was reduced, and the viability of fibroblasts was largely improved. More importantly, the hydrogel coating provided a good buffer zone for cell ingrowth and soft tissue integration. The curbed Zn ion release was also proved to be useful to regulate fibroblast responses such as the expression of CTGF and COL-I. These results were also validated by in vivo studies. Therefore, this study proposed a valid self-adaptive strategy for ZnO improvement. Under different conditions, the sample could present different functions, and both the antibacterial ability and soft tissue compatibility were finely preserved.

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Enzymatically-degradable hydrogel coatings are prepared on the ZnO structure of titanium.

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The degradation of the hydrogel coating is accelerated when S. aureus exists and the remarkable antibacterial activity of ZnO is presented.

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The hydrogel coating is stable and tightly adhered on ZnO when no bacteria exists and the toxicity of ZnO is largely reduced.

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The fibroblast responses and soft tissue compatibility are improved.

Influence of surfactant-tailored Mn-doped ZnO nanoparticles on ROS production and DNA damage induced in murine fibroblast cells

The present study concerns the in vitro oxidative stress responses of non-malignant murine cells exposed to surfactant-tailored ZnO nanoparticles (NPs) with distinct morphologies and different levels of manganese doping. Two series of Mn-doped ZnO NPs were obtained by coprecipitation synthesis method, in the presence of either polyvinylpyrrolidone (PVP) or sodium hexametaphosphate (SHMTP). The samples were investigated by powder X-ray Diffraction, Transmission Electron Microscopy, Fourier-Transform Infrared and Electron Paramagnetic Resonance spectroscopic methods, and N₂ adsorption-desorption analysis. The observed surfactant-dependent effects concerned: i) particle size and morphology; ii) Mn-doping level; iii) specific surface area and porosity. The relationship between the surfactant dependent characteristics of the Mn-doped ZnO NPs and their in vitro toxicity was assessed by studying the cell viability, intracellular reactive oxygen species (ROS) generation, and DNA fragmentation in NIH3T3 fibroblast cells. The results indicated a positive correlation between the specific surface area and the magnitude of the induced toxicological effects and suggested that Mn-doping exerted a protective effect on cells by diminishing the pro-oxidative action associated with the increase in the specific BET area. The obtained results support the possibility to modulate the in vitro toxicity of ZnO nanomaterials by surfactant-controlled Mn-doping.

Toxicity of Different Zinc Oxide Nanomaterials at 3 Trophic Levels: Implications for Development of Low-Toxicity Antifouling Agents

Because zinc oxide (ZnO) nanomaterials are used in antifouling and antibacterial solutions, understanding their toxic effects on different aquatic organisms is essential. In the present study, we evaluated the toxicity of ZnO nanoparticles of 10 to 30 nm (ZnONPI) and 80 to 200 nm (ZnONPII), ZnO nanorods (width 80 nm, height 1.7 µm) attached to the support substrate (glass, ZnONRG) and not attached (ZnONRS), as well as Zn²⁺ ions at concentrations ranging from 0.5 to 100 mg/L. Toxicity was evaluated using the microalga Dunaliella salina, the brine shrimp Artemia salina, and the marine bacterium Bacillus cereus. The highest toxicity was observed for ZnONPs (median lethal concentration [LC50] ~15 mg/L) and Zn²⁺ ions (LC50 ~13 mg/L), whereas the lowest toxicity found for ZnO nanorods (ZnONRG LC50 ~60 mg/L; ZnONRS LC50 ~42 mg/L). The presence of the support substrate in case of ZnO nanorods reduced the associated toxicity to aquatic organisms. Smaller ZnONPs resulted in the highest Zn²⁺ ion dissolution among tested nanostructures. Different aquatic organisms responded differently to ZnO nanomaterials, with D. salina and B. cereus being more sensitive than A. salina. Toxicity of nanostructures increased with an increase of the dose and the time of exposure. Supported ZnO nanorods can be used as a low-toxicity alternative for future antimicrobial and antifouling applications. Environ Toxicol Chem 2020;39:1343-1354. © 2020 SETAC.

Lipid-coated ZnO nanoparticles synthesis, characterization and cytotoxicity studies in cancer cell

ZnO nanoparticles are widely used in biological, chemical, and medical fields, but their toxicity impedes their wide application. In this study, pristine ZnO NPs (~ 7 nm; ~ 18 nm; ~ 49 nm) and lipid-coated ZnO NPs (~ 13 nm; ~ 22 nm; ~ 52 nm) with different morphologies were prepared by chemical method and characterized by TEM, XRD, HRTEM, FTIR, and DLS. Our results showed that the lipid-coated ZnO NPs (~ 13 nm; ~ 22 nm; ~ 52 nm) groups improved the colloidal stability, prevented the aggregation and dissolution of nanocrystal particles in the solution, inhibited the dissolution of ZnO NPs into Zn²⁺ cations, and reduced cytotoxicity more efficiently than the pristine ZnO NPs (~ 7 nm; ~ 18 nm; ~ 49 nm). Compared to the lipid-coated ZnO NPs, pristine ZnO NPs (~ 7 nm; ~ 18 nm; ~ 49 nm) could dose-dependently destroy the cells at low concentrations. At the same concentration, ZnO NPs (~ 7 nm) exhibited the highest cytotoxicity. These results could provide a basis for the toxicological study of the nanoparticles and direct future investigations for preventing strong aggregation, reducing the toxic effects of lipid-bilayer and promoting the uptake of nanoparticles by HeLa cells efficiently.

Quantitative evaluation of the antibacterial factors of ZnO nanorod arrays under dark conditions: Physical and chemical effects on Escherichia coli inactivation

Although zinc oxide nanorod (ZnO NR) arrays are a nanomaterial that offers efficient bactericidal activity, they have not been systematically evaluated to quantitatively investigate their disinfection mechanism under dark conditions. In this study, ZnO NR arrays of different lengths (0.5-4 μm) were uniformly grown via hydrothermal synthesis. The longer arrays exhibited higher Escherichia coli (E. coli) inactivation efficiency up to 94.2% even under darkness for 30 min. When the NR arrays were coated via Al₂O₃ atomic layer deposition, the inactivation efficiency was decreased to 56.4% because the generation of reactive oxygen species (ROS) and the leaching of Zn²⁺ ions were both hindered by the surficial coverage of defect sites. The morphological effect, i.e., the mechanical rupture of E. coli on the surface, contributed 56.4% of the bactericidal efficiency; chemical effects, i.e., ROS formation and zinc ion release, contributed the remaining 37.8% under dark conditions. The bactericidal effect of fabricated ZnO NR arrays was further validated in bottled and pond water spiked with E. coli, exhibiting 87.5% and 80.4% inactivation efficiencies, respectively, within 30 min. Understanding these antibacterial mechanisms is not only of significance for research in this and related fields but also beneficial for potential application in various fields, e.g., biomedical and antifouling areas.

Electrospun Active Biopapers of Food Waste Derived Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with Short-Term and Long-Term Antimicrobial Performance

This research reports about the development by electrospinning of fiber-based films made of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) derived from fermented fruit waste, so-called bio-papers, with enhanced antimicrobial performance. To this end, different combinations of oregano essential oil (OEO) and zinc oxide nanoparticles (ZnONPs) were added to PHBV solutions and electrospun into mats that were, thereafter, converted into homogeneous and continuous films of ~130 μm. The morphology, optical, thermal, mechanical properties, crystallinity, and migration into food simulants of the resultant PHBV-based bio-papers were evaluated and their antimicrobial properties were assessed against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) in both open and closed systems. It was observed that the antimicrobial activity decreased after 15 days due to the release of the volatile compounds, whereas the bio-papers filled with ZnONPs showed high antimicrobial activity for up to 48 days. The electrospun PHBV biopapers containing 2.5 wt% OEO + 2.25 wt% ZnONPs successfully provided the most optimal activity for short and long periods against both bacteria.

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.

Potent and durable antibacterial activity of ZnO-dotted nanohybrids hydrothermally derived from ZnAl-layered double hydroxides

The search for effective alternatives to traditional antibiotics to avoid antibiotic resistant bacteria is growing worldwide. ZnO nanoparticles are found to effectively inhibit growth and proliferation of bacteria, and ZnO-based layered double hydroxides (ZnO-based LDHs) have been intensively investigated for this purpose. However, the nanocomposites are made in a multi-step preparation process with severe agglomeration and limited bactericidal ability. In this research, ZnO-dotted nanohybrids using Zn₃Al-LDHs as precursors (ZnO-dotted LDHs or ZnO/LDHs) were synthesized under facile hydrothermal conditions. An understanding of the transformation of the LDH precursors to the ZnO/LDHs was conducted with TEM/HRTEM/XRD/FTIR. ZnO/LDHs can be transformed from ZnAl-LDHs, with more ZnO nanodots generated upon heating at 150 and 200 °C for 2 h (Zn₃Al-150, Zn₃Al-200). Zn₃Al-200 nanohybrids showed potent antibacterial activity towards Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) at 100-300 μg/mL for 4 days. Antibacterial activity of Zn₃Al-200 may be attributed to the synergistic effects (ROS, leached Zn²⁺ and physical interaction). This research thus suggests a potential economic approach to prepare ZnO/LDH nanocomposites for avoiding the antibiotic resistant bacteria in environmental engineering or clinic fields.

Preparation of ZnO Nanoparticles with High Dispersibility Based on Oriented Attachment (OA) Process

Understanding nanoparticle growth mechanisms is crucial for the synthesis of nanocrystals with desired biological and chemical properties. Growth of nanocrystals by oriented attachment (OA) is frequently reported as a method supplementary to the classical growth by Ostwald ripening (OR) process. In this work, ZnO nanoparticles (NPs) were prepared by wet chemical method. Size/shape evolution of ZnO NPs in ethanol solution was systematically studied using transmission electron microscopy (TEM), dynamic light scattering (DLS), and X-ray diffraction (XRD). In addition, a detailed process of the nanoparticle growth-based OA mechanism is discussed. Results revealed that reaction conditions affect size/shape of NPs and change their surface structure: prior to OA, the surface of adjacent particles transformed into their "rough" states. We proved that stability of the solution was significantly improved in this state. Such a state is important to design nanoparticles with high stability and as nano-suspensions with special physical and/or chemical properties. This state is a critical step in enhancing OA process.

The Advancing of Zinc Oxide Nanoparticles for Biomedical Applications

Zinc oxide nanoparticles (ZnO NPs) are used in an increasing number of industrial products such as rubber, paint, coating, and cosmetics. In the past two decades, ZnO NPs have become one of the most popular metal oxide nanoparticles in biological applications due to their excellent biocompatibility, economic, and low toxicity. ZnO NPs have emerged a promising potential in biomedicine, especially in the fields of anticancer and antibacterial fields, which are involved with their potent ability to trigger excess reactive oxygen species (ROS) production, release zinc ions, and induce cell apoptosis. In addition, zinc is well known to keep the structural integrity of insulin. So, ZnO NPs also have been effectively developed for antidiabetic treatment. Moreover, ZnO NPs show excellent luminescent properties and have turned them into one of the main candidates for bioimaging. Here, we summarize the synthesis and recent advances of ZnO NPs in the biomedical fields, which will be helpful for facilitating their future research progress and focusing on biomedical fields.

Combating pathogens with Cs2.5H0.5PW12O40 nanoparticles: a new proton-regulated antimicrobial agent

The transfer of pathogens from contaminated surfaces to patients is one of the main causes of health care-associated infections (HCAIs). Cases of HCAIs due to multidrug-resistant organisms have been growing worldwide, whereas inorganic nano-antimicrobials are valuable today for the prevention and control of HCAIs. Here, we present a cesium salt of phosphotungstic heteropolyacid (Cs_2.5H_0.5PW₁₂O₄₀) as a promising nanomaterial for use in antimicrobial product technologies. This water-insoluble Keggin salt exhibits a broad biocide spectrum against Gram-positive and Gram-negative bacteria, yeasts, and filamentous fungi even under dark conditions. The Cs_2.5H_0.5PW₁₂O₄₀ nanoparticles (NPs) act as a proton-regulated antimicrobial whose activity is mediated on the release of hydronium ions (H₃O⁺), yielding an in situ acidic pH several units below those tolerable by most of the fungal and bacterial nosocomial pathogens.

Assessment of photocatalytic potentiality and determination of ecotoxicity (using plant model for better environmental applicability) of synthesized copper, copper oxide and copper-doped zinc oxide nanoparticles

NPS SYNTHESIS, CHARACTERIZATION AND AZO-DYE DEGRADATION

A facile cost effective wet chemical method of synthesis is proposed for Cu-NPs, CuO-NPs and Cu-doped ZnO-NPs. The nanomaterials are opto-physically characterized for nano standard quality. Cu-doped ZnO-NPs based catalytic system is found to possess most efficient photocatalytic activity in degradation of two organic azo-dyes namely methyl red (MR) and malachite green (MG) that are released as industrial effluents in eco-environment intercollegium. Two possible photocatalytic degradation pathways are proposed to understand the mechanism of interaction prevailing during the mineralization of MR and MG dyes. Such study provides insight for waste water management. The uniqueness of the present work is 1) possible routes of MG dye degradation by Cu-doped ZnO-NPs and subsequent intermediate by-products are novel and pioneered of its kind. 2) two new intermediate byproducts are identified suggesting prevalence of multiple MR degradation pathways by Cu-doped ZnO-NPs.

ASSESSMENT OF ECOTOXICITY

For assessment of residual NPs impact on environment, eco-toxicological assay is performed using plant system (Sesamum indicum L.) as model. The study encompasses seed germination, seedling morphology, quantification of endogenous H2O2 and MDA generation, estimation of DNA double strand break and analysis of cell cycle inhibition. Results highlight reduced ecotoxicity of Cu-doped ZnO-NPs compared to the other synthesized nanomaterials thereby suggesting better environmental applicability in waste water purification.

Novel folic acid conjugated Fe3O4-ZnO hybrid nanoparticles for targeted photodynamic therapy

A novel folic acid conjugated core-shell hybrid iron oxide-zinc oxide nanoparticle was developed for applications as a photosensitier (PS) in photodynamic therapy. Photodegradation studies on methylene blue demonstrated significantly enhanced photophysical properties of the produced nano-PSs, due to the charge recombination via electron trapping by dissolved Fe³⁺. A time and dose dependant toxicity associated with the nano-PSs was observed upon exposure to human epithelial colorectal adenocarcinoma (Caco-2) cells in the dark. UV irradiation of the synthesised nano-PSs resulted in a significant photo-killing effect with drastic reduction in Caco-2 cell viability to as low as 6%. Reduction in viability upon exposure was due fundamentally to cellular interactions with light irradiated PSs as the influence of radiation alone was subtracted. FA conjugation further enhanced the photo-killing effect.

Sol-gel synthesis of thorn-like ZnO nanoparticles endorsing mechanical stirring effect and their antimicrobial activities: Potential role as nano-antibiotics

The effect of mechanical stirring on sol-gel synthesis of thorn-like ZnO nanoparticles (ZnO-NPs) and antimicrobial activities is successfully reported in this study. The in-house synthesized nanoparticles were characterized by XRD, SEM, TEM, FTIR, TGA, DSC and UV-visible spectroscopy. The X-Ray Diffraction analysis revealed the wurtzite crystal lattice for ZnO-NPs with no impurities present. The diametric measurements of the synthesized thorn-like ZnO-NPs (morphology assessed by SEM) were well accounted to be less than 50 nm with the help of TEM. Relative decrease in aspect ratio was observed on increasing the agitation speed. The UV-visible spectroscopy showed the absorption peaks of the ZnO-NPs existed in both UVA and UVB region. A hypsochromic shift in λmax was observed when stirring pace was increased from 500 rpm to 2000 rpm. The FTIR spectroscopy showed the absorption bands of the stretching modes of Zn-O between 500 cm⁻¹ to 525 cm⁻¹. The Thermal analysis studies revealed better stability for ZnO-NPs prepared at 2000 rpm (ZnO-2000 rpm). TGA revealed the weight loss between two main temperatures ranges viz. around (90 °C–120 °C) and (240 °C–280 °C). Finally, the effect of ZnO-NPs prepared at different stirring conditions on the growth of Gram-positive (Bacillus subtilis), Gram-negative (Escherichia coli) bacteria and a fungi (Candida albicans) were examined; which showed good antibacterial as well as antifungal properties. These findings introduce a simple, inexpensive process to synthesize ZnO-NPs using conventional methods without the use of sophisticated equipments and its application as a potent nano-antibiotic.

Insight into Biological Effects of Zinc Oxide Nanoflowers on Bacteria: Why Morphology Matters

Zinc oxides have gained exciting achievements in antimicrobial fields because of their advantageous properties, whereas their biological effects on bacteria are currently underexplored. In this study, biological effects of flower-shaped nano zinc oxides on bacteria were systematically investigated. Zinc oxide nanoflowers with controllable morphologies (viz., rod flowers, fusiform flowers, and petal flowers) were synthesized by modulating merely base type and concentration using the hydrothermal process. Their antibacterial power is in an order of petal flowers > fusiform flowers > rod flowers because of their differences in microscopic parameters such as specific surface area, pore size, and Zn-polar plane, etc. More importantly, the role of morphology in influencing biological effect on bacteria was examined, focusing on the morphology-induced effect on integrality of cell wall, permeability of cell membrane, DNA cleavage, etc. As for cytotoxicity, all petal flowers, fusiform flowers, and rod flowers show trivial cytotoxicity to the Hela cells. This work provides a guide for enhancing biological effect of the biocides on pathogenic bacteria by the morphological modulation.

Trace amounts of Cu²⁺ ions influence ROS production and cytotoxicity of ZnO quantum dots

3-Aminopropyltrimethoxysilane (APTMS) was used as ligand to prepare ZnO@APTMS, Cu(2+)-doped ZnO (ZnO:Cu@APTMS) and ZnO quantum dots (QDs) with chemisorbed Cu(2+) ions at their surface (ZnO@APTMS/Cu). The dots have a diameter of ca. 5 nm and their crystalline and phase purities and composition were established by X-ray diffraction, transmission electron microscopy, UV-visible and fluorescence spectroscopies and by X-ray photoelectron spectroscopy. The effect of Cu(2+) location on the ability of the QDs to generate reactive oxygen species (ROS) under light irradiation was investigated. Results obtained demonstrate that all dots are able to produce ROS (OH, O2(-), H2O2 and (1)O2) and that ZnO@APTMS/Cu QDs generate more OH and O2(-) radicals and H2O2 than ZnO@APTMS and ZnO:Cu@APTMS QDs probably via mechanisms associating photo-induced charge carriers and Fenton reactions. In cytotoxicity experiments conducted in the dark or under light exposure, ZnO@APTMS/Cu QDs appeared slightly more deleterious to Escherichia coli cells than the two other QDs, therefore pointing out the importance of the presence of Cu(2+) ions at the periphery of the nanocrystals. On the other hand, with the lack of photo-induced toxicity, it can be inferred that ROS production cannot explain the cytotoxicity associated to the QDs. Our study demonstrates that both the production of ROS from ZnO QDs and their toxicity may be enhanced by chemisorbed Cu(2+) ions, which could be useful for medical or photocatalytic applications.

Cytotoxicity of folic acid conjugated hollow silica nanoparticles toward Caco2 and 3T3 cells, with and without encapsulated DOX

Hollow silica nanoparticles of two sizes with and without a folic acid targeting ligand were synthesized. Fickian diffusion of the antitumor drug doxorubicin hydrochloride (DOX) was demonstrated by the produced nanoparticles, achieving a cumulative release of 73% and 45% for 215 nm and 430 nm particles respectively over a period of 500 h. The hollow silica nanoparticles presented a time and dose dependent toxicity, selective to human epithelial colorectal adenocarcinoma (Caco2) cells, over mouse embryonic fibroblast (3T3) cells. At 24h Caco2 cell viability was reduced to 66% using pure hollow silica at a concentration of 50 μg mL(-1), while that of 3T3 cells remained at 94% under the same conditions. The selective cytotoxicity of hollow silica nanoparticles was further enhanced by conjugation of folic acid and incorporation of DOX: at 24h and an equivalent DOX concentration of 0.5 μg mL(-1), viable Caco2 cells were reduced to 45% while 3T3 cells were reduced to 83%. Interestingly the equivalent dose of free DOX was more toxic to 3T3 than to Caco2 cells, reducing the 3T3 viability to 72% and the Caco2 viability to 80%, which is likely due to the presence of the p-glycoprotein pumps in Caco2 cells. Folic acid conjugation served to enhance the viability of both cell lines in this work. Careful optimization of the folate content should further improve the cell specificity of the hollow silica nanoparticles, thus providing a viable targeting platform for cancer therapy.

Zinc oxide nanoparticle suspensions and layer-by-layer coatings inhibit staphylococcal growth

Despite a decade of engineering and process improvements, bacterial infection remains the primary threat to implanted medical devices. Zinc oxide nanoparticles (ZnO-NPs) have demonstrated antimicrobial properties. Their microbial selectivity, stability, ease of production, and low cost make them attractive alternatives to silver NPs or antimicrobial peptides. Here we sought to (1) determine the relative efficacy of ZnO-NPs on planktonic growth of medically relevant pathogens; (2) establish the role of bacterial surface chemistry on ZnO-NP effectiveness; (3) evaluate NP shape as a factor in the dose-response; and (4) evaluate layer-by-layer (LBL) ZnO-NP surface coatings on biofilm growth. ZnO-NPs inhibited bacterial growth in a shape-dependent manner not previously seen or predicted. Pyramid shaped particles were the most effective and contrary to previous work, larger particles were more effective than smaller particles. Differential susceptibility of pathogens may be related to their surface hydrophobicity. LBL ZnO-NO coatings reduced staphylococcal biofilm burden by >95%. From the Clinical Editor: The use of medical implants is widespread. However, bacterial colonization remains a major concern. In this article, the authors investigated the use of zinc oxide nanoparticles (ZnO-NPs) to prevent bacterial infection. They showed in their experiments that ZnO-NPs significantly inhibited bacterial growth. This work may present a new alternative in using ZnO-NPs in medical devices.

Toxicity of metal oxide nanoparticles: mechanisms, characterization, and avoiding experimental artefacts

Metal oxide nanomaterials are widely used in practical applications and represent a class of nanomaterials with the highest global annual production. Many of those, such as TiO2 and ZnO, are generally considered non-toxic due to the lack of toxicity of the bulk material. However, these materials typically exhibit toxicity to bacteria and fungi, and there have been emerging concerns about their ecotoxicity effects. The understanding of the toxicity mechanisms is incomplete, with different studies often reporting contradictory results. The relationship between the material properties and toxicity appears to be complex and diifficult to understand, which is partly due to incomplete characterization of the nanomaterial, and possibly due to experimental artefacts in the characterization of the nanomaterial and/or its interactions with living organisms. This review discusses the comprehensive characterization of metal oxide nanomaterials and the mechanisms of their toxicity.

A general, eco-friendly synthesis procedure of self-assembled ZnO-based materials with multifunctional properties

One way of getting green: saccharides in cooperation with triethanolamine are proposed as green and versatile tools for the synthesis of ZnO-based materials.