Palladium – Decorated reduced graphene oxide/zinc oxide nanocomposite for enhanced antimicrobial, antioxidant and cytotoxicity activities

A review on antimicrobial mechanism and applications of graphene-based materials

In recent years, graphene and its derivatives, owing to their phenomenal surface, and mechanical, electrical, and chemical properties, have emerged as advantageous materials, especially in terms of their potential for antimicrobial applications. Particularly important among graphene's derivatives is graphene oxide (GO) due to the ease with which its surface can be modified, as well as the oxidative and membrane stress that it exerts on microbes. This review encapsulates all aspects regarding the functionalization of graphene-based materials (GBMs) into composites that are highly potent against bacterial, viral, and fungal activities. Governing factors, such as lateral size (LS), number of graphene layers, solvent and GBMs' concentration, microbial shape and size, aggregation ability of GBMs, and especially the mechanisms of interaction between composites and microbes are discussed in detail. The current and potential applications of these antimicrobial materials, especially in dentistry, osseointegration, and food packaging, have been described. This knowledge can further drive research that aims to look for the most suitable components for antimicrobial composites. The need for antimicrobial materials has seldom been more felt than during the COVID-19 pandemic, which has also been highlighted here. Possible future research areas include the exploration of GBMs' ability against algae.

Nanoantioxidant Materials: Nanoengineering Inspired by Nature

Oxidants are very active compounds that can cause damage to biological systems under specific environmental conditions. One effective way to counterbalance these adverse effects is the use of anti-oxidants. At low concentrations, an antioxidant is defined as a compound that can delay, control, or prevent an oxidative process. Antioxidants exist in plants, soil, and minerals; therefore, nature is a rich source of natural antioxidants, such as tocopherols and polyphenols. In nature, antioxidants perform in tandem with their bio-environment, which may tune their activity and protect them from degradation. In vitro use of antioxidants, i.e., out of their biomatrix, may encounter several drawbacks, such as auto-oxidation and polymerization. Artificial nanoantioxidants can be developed via surface modification of a nanoparticle with an antioxidant that can be either natural or synthetic, directly mimicking a natural antioxidant system. In this direction, state-of-the-art nanotechnology has been extensively incorporated to overcome inherent drawbacks encountered in vitro use of antioxidants, i.e., out of their biomatrix, and facilitate the production and use of antioxidants on a larger scale. Biomimetic nanoengineering has been adopted to optimize bio-medical antioxidant systems to improve stability, control release, enhance targeted administration, and overcome toxicity and biocompatibility issues. Focusing on biotechnological sciences, this review highlights the importance of nanoengineering in developing effective antioxidant structures and comparing the effectiveness of different nanoengineering methods. Additionally, this study gathers and clarifies the different antioxidant mechanisms reported in the literature and provides a clear picture of the existing evaluation methods, which can provide vital insights into bio-medical applications.

Biogenic synthesis of reduced graphene oxide from Ziziphus spina-christi (Christ's thorn jujube) extracts for catalytic, antimicrobial, and antioxidant potentialities

In the current work, various concentrations of the aqueous extract of Ziziphus spina-christi were employed for the phytoreduction of graphene oxide (GO). The green synthesized reduced graphene oxide (rGO) was characterized through UV-Vis spectrometry, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy, and energy-dispersive X-ray spectroscopy (SEM-EDX). Gas chromatography-mass spectrometry (GC-MS) denoted the presence of numerous phytoconstituents including ketones, terpenoids, fatty acids, esters, and flavonoids, which acted as reducing and capping agents. The obtained results indicated the increase in rGO yield and shape with increasing the extract concentration. The optimized rGO was instantaneously ~100% removed methylene blue (MB) from the water at 5 mg L^-1. However, the removal efficiency was slightly declined to reach 73.55 and 65.1% at 10 and 15 mg L^-1, respectively. A powerful antibacterial activity for rGO particularly against gram-negative bacteria with a high concentration of 2 × 10⁸ CFU mL^-1 was confirmed. Furthermore, rGO demonstrated promising and comparable antioxidant efficiency with vitamin C against DPPH free radical scavenging. While vitamin C recorded 13.45 and 48.4%, the optimized rGO attained 13.30 and 45.20% at 12 and 50 μg mL^-1, respectively.

Novel Nd-N/TiO2 Nanoparticles for Photocatalytic and Antioxidant Applications Using Hydrothermal Approach

In this study, photocatalysis was employed to degrade a wastewater pollutant (AB-29 dye) under visible light irradiation. For this purpose, nitrogen (N)- and neodymium (Nd)-doped TiO₂ nanoparticles were prepared using the simple hydrothermal method. X-ray diffraction (XRD) revealed an anatase phase structure of the Nd-N/TiO₂ photocatalyst, whereas properties including the surface morphology, chemical states/electronics structure and optical structure were determined using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-visible (UV-vis.) and photoluminescence (PL) spectroscopies. Photocatalytic testing of the prepared nanomaterials was performed to remove acid blue-29 (AB-29) dye under visible-light exposure. The prepared Nd-N/TiO₂ nanoparticles demonstrated a superior photocatalytic activity and the decolorization efficiency was about 92% after visible-light illumination for 1 h and 20 min, while N/TiO₂, Nd/TiO₂ and TiO₂ only showed a 67%, 43% and 31% decolorization efficiency, respectively. The enhanced photocatalytic activity of the Nd-N/TiO₂ photocatalyst was due to a decrease in the electron/hole's recombination and the increased absorption of TiO₂ in the visible range. The reusability results showed that the average photocatalytic activity decrease for all the samples was only about 16% after five consecutive cycles, indicating a good stability of the prepared nanomaterials. Moreover, the radical scavenging activity of the prepared nanomaterials was evaluated using the DPPH method. The novel Nd-N/TiO₂ exhibited a higher antioxidant activity compared to all the other samples.

Palladium and Graphene Oxide Doped ZnO for Aqueous Acetamiprid Degradation under Visible Light

Acetamiprid is a neonicotinoid insecticide widely used in pest control. In recent years, it has been considered as a contaminant in groundwater, lakes, and rivers. Photocatalysis under visible light radiation proved to be an effective process for getting rid of several organic pollutants. In the present work, photodegradation of aqueous acetamiprid was investigated over bare zinc oxide (ZnO) photocatalyst as well as ZnO doped with either palladium or palladium combined with graphene oxide. Both ZnO and doped-ZnO were synthesized via a microwave-assisted hydrothermal procedure. The obtained photocatalysts were characterized using different techniques. After 5 h of reaction at ambient temperature under visible light irradiation, acetamiprid conversions attained ca. 38, 82, and 98% in the presence of bare ZnO, Pd-doped ZnO and Pd-GO-doped ZnO photocatalysts, respectively, thus demonstrating the positive effect of Pd- and GO-doping on the photocatalytic activity of ZnO. In addition, Pd-GO-doped ZnO was shown to keep its activity even when it is recycled five times, thus proving its stability in the reaction medium.

Green synthesis of bimetallic Ag/ZnO@Biohar nanocomposite for photocatalytic degradation of tetracycline, antibacterial and antioxidant activities

In this work, a simple and green synthesis procedure for phytofabrication Zinc oxide-silver supported biochar nanocomposite (Ag/ZnO@BC) via Persicaria salicifolia biomass is investigated for the first time to uphold numerous green chemistry such as less hazardous chemical syntheses. XRD technique showed the crystal structure of the phytosynthesized Ag/ZnO@BC, whereas UV-visible spectroscopy, FT-IR, SEM, EDX, TEM, and XPS analyses indicated the successful biosynthesis of the nanocomposite. Testing the photocatalytic potential of this novel nanocomposite in the removal of TC under different conditions unraveled its powerful photodegradation efficiency that reached 70.3% under the optimum reaction conditions: TC concentration; 50 ppm, pH; 6, a dose of Ag/ZnO@BC; 0.01 g, temperature; 25 °C, and H₂O₂ concentration; 100 mM. The reusability of Ag/ZnO@BC was evident as it reached 53% after six cycles of regeneration. Ag/ZnO@BC was also shown to be a potent antimicrobial agent against Klebsiella pneumonia as well as a promising antioxidant material. Therefore, the current work presented a novel nanocomposite that could be efficiently employed in various environmental and medical applications.

Potential Impact of Reduced Graphene Oxide Incorporated Metal Oxide Nanocomposites as Antimicrobial, and Antibiofilm Agents Against Pathogenic Microbes: Bacterial Protein Leakage Reaction Mechanism

In the current study, nanocomposites-based reduced graphene oxide (RGO) and metal oxides (AgO, NiO, and ZnO) were fabricated. The starting precursor and RGO were characterized by XRD, Raman, SEM, and HRTEM, while SEM and EDX mapping validated the synthesized nanocomposites. In addition, ZOI, MIC, antibiofilm, and growth curve were tested. The antimicrobial reaction mechanism was investigated by protein leakage assay and SEM imaging. Results revealed that all synthesized nanocomposites (RGO-AgO, RGO-NiO, and RGO-ZnO) have outstanding antimicrobial activity against pathogenic bacteria and unicellular fungi. Moreover, RGO-AgO, RGO-NiO, and RGO-ZnO nanocomposites exhibited an antibiofilm activity percentage against Staphylococcus aureus (91.72%), Candida albicans  (91.17%), and Escherichia coli (90.36%). The SEM analysis of S. aureus after RGO-AgO treatment indicated morphological differences, including the whole lysis of the outer surface supported by deformations of the bacterial cells. It was observed that the quantity of cellular protein leakage from S. aureus is directly proportional to the concentration of RGO-AgO, RGO-NiO, and RGO-ZnO nanocomposites and found to be 260.25 µg/mL, 110.55 µg/mL, and 99.90 µg/mL, respectively. The prepared nanocomposites promise to treat resistant microbes as a new strategy for managing infectious diseases.

Catalytic and Medical Potential of a Phyto-Functionalized Reduced Graphene Oxide-Gold Nanocomposite Using Willow-Leaved Knotgrass

In the current study, a simple, environmentally friendly, and cost-effective reduced graphene oxide-gold nanoparticle (rGO-AuNP) nanocomposite was successfully phytosynthesized using the aqueous leaf extract of a common weed found on the Nile banks, Persicaria salicifolia, for the first time. The phytosynthesis of rGO-AuNPs was first confirmed via the color transformation from brown to black as well as throughvarious techniques such as transmission electron microscopy (TEM) and Raman spectroscopy. Two UV-vis peaks at 275 and 530 nm were observed for the nanocomposite with a typical particle size of mostly spherical AuNPs of 15-20 nm. However, other shapes were occasionally detected including rods, triangles, and rhomboids. Existing phytoconstituents such as flavonoids and glycosides in the plant extract were suggested to be responsible for the phytosynthesis of rGO-AuNPs. The excellent catalytic efficacy of rGO-AuNPs against MB degradation was confirmed, and a high antibacterial efficiency against Escherichia coli and Klebsiella pneumonia was also confirmed. Promising antioxidant performance of rGO-AuNPs was also proved. Furthermore, it was concluded that rGO-AuNPs acquired higher efficiency than AuNPs synthesized from the same plant extract in all of the studied applications.

Nanoantioxidants: Pioneer Types, Advantages, Limitations, and Future Insights

Free radicals are generated as byproducts of normal metabolic processes as well as due to exposure to several environmental pollutants. They are highly reactive species, causing cellular damage and are associated with a plethora of oxidative stress-related diseases and disorders. Antioxidants can control autoxidation by interfering with free radical propagation or inhibiting free radical formation, reducing oxidative stress, improving immune function, and increasing health longevity. Antioxidant functionalized metal nanoparticles, transition metal oxides, and nanocomposites have been identified as potent nanoantioxidants. They can be formulated in monometallic, bimetallic, and multi-metallic combinations via chemical and green synthesis techniques. The intrinsic antioxidant properties of nanomaterials are dependent on their tunable configuration, physico-chemical properties, crystallinity, surface charge, particle size, surface-to-volume ratio, and surface coating. Nanoantioxidants have several advantages over conventional antioxidants, involving increased bioavailability, controlled release, and targeted delivery to the site of action. This review emphasizes the most pioneering types of nanoantioxidants such as nanoceria, silica nanoparticles, polydopamine nanoparticles, and nanocomposite-, polysaccharide-, and protein-based nanoantioxidants. This review overviews the antioxidant potential of biologically synthesized nanomaterials, which have emerged as significant alternatives due to their biocompatibility and high stability. The promising nanoencapsulation nanosystems such as solid lipid nanoparticles, nanostructured lipid carriers, and liposome nanoparticles are highlighted. The advantages, limitations, and future insights of nanoantioxidant applications are discussed.

Turning Toxic Nanomaterials into a Safe and Bioactive Nanocarrier for Co-delivery of DOX/pCRISPR

Hybrid bioactive inorganic-organic carbon-based nanocomposites of reduced graphene oxide (rGO) nanosheets enlarged with multi-walled carbon nanotubes (MWCNTs) were decorated to provide a suitable space for in situ growth of CoNi₂S₄ and green-synthesized ZnO nanoparticles. The ensuing nanocarrier supplied π-π interactions between the DOX drug and a stabilizing agent derived from leaf extracts on the surface of ZnO nanoparticles and hydrogen bonds; gene delivery of (p)CRISPR was also facilitated by chitosan and alginate renewable macromolecules. Also, these polymers can inhibit the potential interactions between the inorganic parts and cellular membranes to reduce the potential cytotoxicity. Nanocomposite/nanocarrier analyses and sustained DOX delivery (cytotoxicity analyses on HEK-293, PC12, HepG2, and HeLa cell lines after 24, 48, and 72 h) were indicative of an acceptable cell viability of up to 91.4 and 78.8% after 48 at low and high concentrations of 0.1 and 10 μg/mL, respectively. The MTT results indicate that by addition of DOX to the nanostructures, the relative cell viability increased after 72 h of treatment; since the inorganic compartments, specifically CoNi₂S₄, are toxic, this is a promising route to increase the bioavailability of the nanocarrier before reaching the targeted cells. Nanosystems were tagged with (p)CRISPR for co-transfer of the drug/genes, where confocal laser scanning microscopy (CLSM) pictures of the 4',6-diamidino-2-phenylindole (DAPI) were indicative of appropriate localization of DOX into the nanostructure with effective cell and drug delivery at varied pH. Also, the intrinsic toxicity of CoNi₂S₄ does not affect the morphology of the cells, which is a breakthrough. Furthermore, the CLSM images of the HEK-293 and HeLa cell displayed effective transport of (p)CRISPR into the cells with an enhanced green fluorescent protein (EGFP) of up to 8.3% for the HEK-293 cell line and 21.4% for the HeLa cell line, a record. Additionally, the specific morphology of the nanosystems before and after the drug/gene transport events, via images by TEM and FESEM, revealed an intact morphology for these biopolymers and their complete degradation after long-time usage.

Facile multifunctional-mode of fabricated biocompatible human serum albumin/reduced graphene oxide/Cladophora glomeratananoparticles for bacteriostatic phototherapy, bacterial tracking and antioxidant potential

To overcome multi-drug resistance in microbes, highly efficient antimicrobial substances are required that have a controllable antibacterial effect and are biocompatible. In the present study, an efficient phototherapeutic antibacterial agent, human serum albumin (HSA)/reduced graphene oxide (rGO)/Cladophora glomeratabionanocomposite was synthesized by the incorporation of rGO nanoparticles with HSA, forming protein-rGO, and decorated with a natural freshwater seaweedCladophora glomerata. The prepared HSA/rGO/Cladophora glomeratabionanocomposite was characterized by spectroscopic (UV-vis, FTIR, XRD and Raman) and microscopic (TEM and SEM) techniques. The as-synthesized bionanocomposite showed that sunlight/NIR irradiation stimulated ROS-generating dual-phototherapic effects against antibiotic-resistant bacteria. The bionanocomposite exerted strong antibacterial effects (above 96 %) against amoxicillin-resistantP. aeruginosaandS. aureus, in contrast to single-model-phototherapy. The bionanocomposite not only generated abundant ROS for killing bacteria, but also expressed a fluorescence image for bacterial tracking under sunlight/NIR irradiation. Additionally, the bionanocomposite displayed pronounced antioxidant activity.