Ultra-Small Silver Nanoparticles: A Sustainable Green Synthesis Approach for Antibacterial Activity.

The present study centers on the synthesis of ultra-small silver nanoparticles (AgNPs) with antibacterial properties using citrus peel residues (orange, lemon, and grapefruit) as reducing and stabilizing agents, and on assessing their antibacterial activity against multidrug-resistant clinical Staphylococcus aureus. The synthesized AgNPs were analyzed by various techniques, including UV-Vis spectroscopy, SAED, TEM, XRD, FTIR, and Raman. The results demonstrate the formation of ultra-small, monodisperse, quasi-spherical AgNPs with an average particle size of 2.42 nm for AgNPs produced with mixed extracts. XRD analysis indicated that the AgNPs have a crystal size of 9.71 to 16.23 nm. The AgNPs exhibited potent inhibitory activity against resistant S. aureus, with a minimum inhibitory concentration (MIC) of 15.625 to 62.50 ppm. The findings suggest that the ultra-small nanometer size of the AgNPs could be attributed to the synthesis method that employs ambient conditions and the presence of polyphenolic compounds from citrus peel. Consequently, AgNPs obtained through sustainable green synthesis hold significant potential in combating clinical multi-resistant bacterial strains that are challenging to treat and eradicate. This approach also contributes to the revaluation of citrus residues in the region, which is an ongoing environmental issue today.

Synthesis of Copper Nanoparticles Stabilized with Organic Ligands and Their Antimicrobial Properties.

In this work, we report the synthesis of copper nanoparticles (Cu NPs), employing the chemical reduction method in an aqueous medium. We used copper sulfate pentahydrate (CuSO4·5H2O) as a metallic precursor; polyethylenimine (PEI), allylamine (AAM), and 4-aminobutyric acid (AABT) as stabilizing agents; and hydrated hydrazine as a reducing agent. The characterization of the obtained nanoparticles consisted of X-ray, TEM, FTIR, and TGA analyses. Through these techniques, it was possible to detect the presence of the used stabilizing agents on the surface of the NPs. Finally, a zeta potential analysis was performed to differentiate the stability of the nanoparticles with a different type of stabilizing agent, from which it was determined that the most stable nanoparticles were the Cu NPs synthesized in the presence of the PEI/AAM mixture. The antimicrobial activity of Cu/PEI/AABT toward P. aeruginosa and S. aureus bacteria was high, inhibiting both bacteria with low contact times and copper concentrations of 50-200 ppm. The synthesis method allowed us to obtain Cu NPs free of oxides, stable to oxidation, and with high yields. The newly functionalized Cu NPs are potential candidates for antimicrobial applications.

Zinc Oxide Nanoparticles and Zinc Sulfate Impact Physiological Parameters and Boosts Lipid Peroxidation in Soil Grown Coriander Plants (Coriandrum sativum).

The objective of this study was to determine the oxidative stress and the physiological and antioxidant responses of coriander plants (Coriandrum sativum) grown for 58 days in soil with zinc oxide nanoparticles (ZnO NPs) and zinc sulfate (ZnSO4) at concentrations of 0, 100, 200, 300, and 400 mg of Zn/kg of soil. The results revealed that all Zn compounds increased the total chlorophyll content (CHLt) by at least 45%, compared to the control group; however, with 400 mg/kg of ZnSO4, chlorophyll accumulation decreased by 34.6%. Zn determination by induction-plasma-coupled atomic emission spectrometry (ICP-AES) showed that Zn absorption in roots and shoots occurred in plants exposed to ZnSO4 at all concentrations, which resulted in high levels of hydrogen peroxide (H2O2) and malondialdehyde (MDA). Only at 400 mg/kg of ZnSO4, a 78.6% decrease in the MDA levels was observed. According to the results, the ZnSO4 treatments were more effective than the ZnO NPs to increase the antioxidant activity of catalase (CAT), ascorbate peroxidase (APX), and peroxidases (POD). The results corroborate that phytotoxicity was higher in plants subjected to ZnSO4 compared to treatments with ZnO NPs, which suggests that the toxicity was due to Zn accumulation in the tissues by absorbing dissolved Zn++ ions.

Monodisperse Gold Cuboctahedral Nanocrystals Directly Synthesized in Reverse Micelles: Preparation, Colloidal Dispersion in Organic Solvents and Water, Reversible Self-Assembly and Plasmonic Properties.

The synthesis of organic-solvent-dispersible gold nanoparticles in reverse micelles of didodecyldimethylammonium bromide (DDAB) is revisited in the present investigation. Some parameters of synthesis, specifically the reaction volume and the concentration of the reducing agent, were slightly modified obtaining directly monodisperse gold nanocrystals (AuNCs) without the need to use additional active surfactants or additional treatments such as digestive ripening. Interestingly, most of the obtained AuNCs display the same exposed crystalline faces composed of six bounding facets (four {111} faces and two {002} faces), corresponding to single-crystalline face-centered cubic nanoparticles with a cuboctahedron shape. When these AuNCs are subsequently functionalized with 1-decanethiol (C10H21SH) or 1-dodecanethiol (C12H25SH), they don't experience significant changes in their size or crystalline texture, however, they self-aggregate directly in the suspension at room temperature into faceted supramolecular structures and exhibit collective plasmonic excitations. Such self-organization is reversible under heating treatments allowing the observation of the influence of the AuNCs aggregation state on their plasmonic properties. Fourier transform infrared spectroscopy reveals that thiols only replace partially the DDAB molecules, and thus, DDAB molecules remain present in the thiol-capped AuNCs. To turn the thiol-capped nanocrystals into water-dispersible nanocrystals and extend their technological potential, they are stabilized with poloxamer 407 obtaining highly stable purple colloids in water.

Foliar Application of Zinc Oxide Nanoparticles and Zinc Sulfate Boosts the Content of Bioactive Compounds in Habanero Peppers.

The physiological responses of habanero pepper plants (Capsicum chinense Jacq.) to foliar applications of zinc sulphate and zinc nano-fertilizer were evaluated in greenhouse trials. The effect of the supplement on fruit quality of habanero pepper was particularly observed. Habanero pepper plants were grown to maturity, and during the main stages of phenological development, they were treated with foliar applications of Zn at concentrations of 1000 and 2000 mg L-1 in the form of zinc sulfate (ZnSO4) and zinc oxide nanoparticles (ZnO NPs). Additional Zn was not supplied to the control treatment plants. ZnO NPs at a concentration of 1000 mg L-1 positively affected plant height, stem diameter, and chlorophyll content, and increased fruit yield and biomass accumulation compared to control and ZnSO4 treatments. ZnO NPs at 2000 mg L-1 negatively affected plant growth but significantly increased fruit quality, capsaicin content by 19.3%, dihydrocapsaicin by 10.9%, and Scoville Heat Units by 16.4%. In addition, at 2000 ZnO NPs mg L-1 also increased content of total phenols and total flavonoids (soluble + bound) in fruits (14.50% and 26.9%, respectively), which resulted in higher antioxidant capacity in ABTS (2,2'azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)), DPPH (2,2-diphenyl-1-picrylhydrazyl), and FRAP (ferric reducing antioxidant power) (15.4%, 31.8%, and 20.5%, respectively). These results indicate that application of ZnO NPs could be employed in habanero pepper production to improve yield, quality, and nutraceutical properties of fruits.

Hollow ZnO microspheres functionalized with electrochemical graphene oxide for the photodegradation of salicylic acid.

Hollow ZnO microspheres were successfully synthesized by a hydrothermal method and then functionalized with graphene oxide (GO) flakes, previously obtained through electrochemical oxidation. Their photocatalytic activity toward the photodegradation of salicylic acid under UV light irradiation was evaluated by UV-Vis spectroscopy. Unfunctionalized microspheres and ZnO functionalized with chemically oxidized graphene were also studied as comparative terms. The hybrid materials of ZnO with both electrochemical and chemical GO gave a similar photodegradation yield of ∼28% against 18% of the non-functionalized microspheres. The similar degradation yields and rate constants obtained with the two GO synthetic methods indicate that electrochemical oxidation of GO represents an eco-friendly option over traditional methods for photocatalytic degradation systems.

Early Stages of Antibacterial Damage of Metallic Nanoparticles by TEM and STEM-HAADF.

BACKGROUND: Propagation of pathogens has considered an important health care problem due to their resistance against conventional antibiotics. The recent challenge involves the design of functional alternatives such as nanomaterials, used as antibacterial agents. Early stages of antibacterial damage caused by metallic nanoparticles (NPs) were studied by Transmission Electron Microscopy (TEM) and combined Scanning Transmission Electron Microscopy with High Angle Annular Dark Field (STEM-HAADF), aiming to contribute to the elucidation of the primary antibacterial mechanism of metallic NPs. METHODS: We analyze the NPs morphology by TEM and their antibacterial activity (AA) with different amounts of Ag and Cu NPs. Cultured P. aeruginosa were interacted with both NPs and processed by TEM imaging to determine NPs adhesion into bacteria wall. Samples were analyzed by combined STEM-HAADF to determine the NPs penetration into bacterium and elemental mapping were done. RESULTS: Both NPs displays AA depending on NPs concentration. TEM images show NPs adhesion on bacterial cells, which produces morphological changes in the structure of the bacteria. STEM-HAADF also proves the NPs adhesion and penetration by intracellular localization, detecting Ag/Cu species analyzed by elemental mapping. Moreover, the relative amount of phosphorus (P) and sulfur (S) increases slightly in P. aeruginosa with the presence of NPs. These elements are associated with damaged proteins of the outer cell membrane. CONCLUSIONS: Combined microscopy analyses suggest that the early stages of antibacterial damage caused by alteration of bacterial cell wall, and can be considered a powerful tool aiming to understand the primary antibacterial mechanism of NPs.

Microstructural, spectroscopic, and antibacterial properties of silver-based hybrid nanostructures biosynthesized using extracts of coriander leaves and seeds.

Coriander leaves and seeds have been highly appreciated since ancient times, not only due to their pleasant flavors but also due to their inhibitory activity on food degradation and their beneficial properties for health, both ascribed to their strong antioxidant activity. Recently, it has been shown that coriander leaf extracts can mediate the synthesis of metallic nanoparticles through oxidation/reduction reactions. In the present study, extracts of coriander leaves and seeds have been used as reaction media for the wet chemical synthesis of ultrafine silver nanoparticles and nanoparticle clusters, with urchin- and tree-like shapes, coated by biomolecules (mainly, proteins and polyphenols). In this greener route of nanostructure preparation, the active biocompounds of coriander simultaneously play the roles of reducing and stabilizing agents. The morphological and microstructural studies of the resulting biosynthesized silver nanostructures revealed that the nanostructures prepared with a small concentration of the precursor Ag salt (AgNO3 =5 mM) exhibit an ultrafine size and a narrow size distribution, whereas particles synthesized with high concentrations of the precursor Ag salt (AgNO3 =0.5 M) are polydisperse and formation of supramolecular structures occurs. Fourier transform infrared and Raman spectroscopy studies indicated that the bioreduction of the Ag- ions takes place through their interactions with free amines, carboxylate ions, and hydroxyl groups. As a consequence of such interactions, residues of proteins and polyphenols cap the biosynthesized Ag nanoparticles providing them a hybrid core/shell structure. In addition, these biosynthesized Ag nanomaterials exhibited size-dependent plasmon extinction bands and enhanced bactericidal activities against both Gram-positive and Gram-negative bacteria, displaying minimal inhibitory Ag concentrations lower than typical values reported in the literature for Ag nanoparticles, probably due to the synergy of the bactericidal activities of the Ag nanoparticle cores and their capping ligands.

Biosynthesis of silver fine particles and particles decorated with nanoparticles using the extract of Illicium verum (star anise) seeds.

Given the upsurge of new technologies based on nanomaterials, the development of sustainable methods to obtain functional nanostructures has become an imperative task. In this matter, several recent researches have shown that the biodegradable natural antioxidants of several plant extracts can be used simultaneously as reducing and stabilizing agents in the wet chemical synthesis of metallic nanoparticles, opening new opportunities to design greener synthesis. However, the challenge of these new techniques is to produce stable colloidal nanoparticles with controlled particle uniformity, size, shape and aggregation state, in similar manner than the well-established synthetic methods. In the present work, colloidal metallic silver nanoparticles have been synthesized using silver nitrate and extracts of Illicium verum (star anise) seeds at room temperature in a facile one-step procedure. The resulting products were colloidal suspensions of two populations of silver nanoparticles, one of them with particle sizes of few nanometers and the other with particles of tens of nm. Strikingly, the variation of the AgNO3/extract weight ratio in the reaction medium yielded to the variation of the spatial distribution of the nanoparticles: high AgNO3/extract concentration ratios yielded to randomly dispersed particles, whereas for lower AgNO3/extract ratios, the biggest particles appeared coated with the finest nanoparticles. This biosynthesized colloidal system, with controlled particle aggregation states, presents plasmonic and SERS properties with potential applications in molecular sensors and nanophotonic devices.

Electroplating and magnetostructural characterization of multisegmented Co54Ni46/Co85Ni15 nanowires from single electrochemical bath in anodic alumina templates.

Highly hexagonally ordered hard anodic aluminum oxide membranes, which have been modified by a thin cover layer of SiO2 deposited by atomic layer deposition method, were used as templates for the synthesis of electrodeposited magnetic Co-Ni nanowire arrays having diameters of around 180 to 200 nm and made of tens of segments with alternating compositions of Co54Ni46 and Co85Ni15. Each Co-Ni single segment has a mean length of around 290 nm for the Co54Ni46 alloy, whereas the length of the Co85Ni15 segments was around 430 nm. The composition and crystalline structure of each Co-Ni nanowire segment were determined by transmission electron microscopy and selected area electron diffraction techniques. The employed single-bath electrochemical nanowire growth method allows for tuning both the composition and crystalline structure of each individual Co-Ni segment. The room temperature magnetic behavior of the multisegmented Co-Ni nanowire arrays is also studied and correlated with their structural and morphological properties.

Control of crystallite orientation and size in Fe and FeCo nanoneedles.

Uniform magnetic nanoneedles have been prepared by hydrogen reduction of elongated nanoarchitectures. These precursors are as-prepared or cobalt-coated aggregates of highly oriented haematite nanocrystals (∼5 nm). The final materials are flattened nanoneedles formed by chains of assembled Fe or FeCo single-domain nanocrystals. The microstructural properties of such nanoneedles were tailored using renewed and improved synthetic strategies. In this fashion, the needle elongation and composition, the crystallite size (from 15 up to 30 nm), the nanocrystal orientation (with the 〈110〉 or 〈001〉 directions roughly along the long axis of the nanoneedle) and their type of arrangement (single chains, frustrated double chains and double chains) were controlled by modifying the reduction time, the axial ratio of the precursor haematite and the presence of additional coatings of aluminum or yttrium compounds. The values of the coercivity H(C) found for these nanoneedles are compared with the values predicted by the chain of spheres model assuming a symmetric fanning mechanism for magnetization reversal.