Immobilization Of Silver Nanoparticles Research Articles

Enzyme assisted magnetic hybrids as self-activated cascade reagent with synergistic activity for antimicrobial application

The abuse of antibiotics seriously threatens the public health, which leads to the urgent need to develop novel antimicrobial strategies. Reactive oxygen species (ROS) have been considered as an alternative approach for bacterial inactivation. At present, magnetic materials, especially iron oxide (Fe3O4) nanoparticles have gained widely application in biomedical field. Owing to the intrinsic peroxidase-like activity, Fe3O4 can catalyze the decomposition of hydrogen peroxide (H2O2) to generate hydroxyl radical (⋅OH) under acidic conditions. Recently, Fe3O4-based peroxidase mimics have been developed for wound infection therapy. However, the direct introduction of H2O2 with relative high concentration may induce undesired effect to normal tissues, and the infection site with near neutral pH still limits the antibacterial efficiency. Herein, carboxyl modified Fe3O4 immobilized silver nanoparticles (Ag NPs) and glucose oxidase (GOx) were synthesized as a self-activated cascade regent. GOx endowed the hybrids with catalytic activity, which could convert glucose into gluconic acid, which activated the peroxidase-like activity of Fe3O4 by decreasing the pH value. Moreover, the self-supplied H2O2 was subsequently catalyzed by Fe3O4 to generate ⋅OH. By combining the excellent antimicrobial performance of Ag NPs, the enzyme assisted magnetic hybrids exhibited robust antibacterial activity, which exhibited a great potential in bacteria-infected wound therapy.

Inducing SERS activity at graphitic carbon using graphene-covered Ag nanoparticle substrates: Spectroelectrochemical analysis of a redox-active adsorbed anthraquinone.

Graphitic carbon electrodes are central to many electrochemical energy storage and conversion technologies. Probing the behavior of molecular species at the electrochemical interfaces they form is paramount to understanding redox reaction mechanisms. Combining surface-enhanced Raman scattering (SERS) with electrochemical methods offers a powerful way to explore such mechanisms, but carbon itself is not a SERS activating substrate. Here, we report on a hybrid substrate consisting of single- or few-layer graphene sheets deposited over immobilized silver nanoparticles, which allows for simultaneous SERS and electrochemical investigation. To demonstrate the viability of our substrate, we adsorbed anthraquinone-2,6-disulfonate to graphene and studied its redox response simultaneously using SERS and cyclic voltammetry in acidic solutions. We identified spectral changes consistent with the reversible redox of the quinone/hydroquinone pair. The SERS intensities on bare silver and hybrid substrates were of the same order of magnitude, while no discernible signals were observed over bare graphene, confirming the SERS effect on adsorbed molecules. This work provides new prospects for exploring and understanding electrochemical processes in situ at graphitic carbon electrodes.

Immobilization of silver nanoparticles on cellulose nanofibrils incorporated into nanofiltration membrane for enhanced desalination performance

Nanofiltration (NF) membranes circumventing global water scarcity with excellent separation and antibacterial performances are highly desirable for efficient water treatment but remain a great challenge. Herein, a nanofiltration membrane was fabricated by in situ immobilizing silver nanoparticles (AgNPs) on sulfated cellulose nanofibril incorporated during interfacial polymerization. AgNPs were confirmed to be uniformly distributed and in situ grown on sulfated cellulose nanofibril (SCNF) due to its abundant sulfate and hydroxyl groups by mixing them with anhydrous piperazine solution as inorganic phase and homophenyl chloride n-hexane solution as the organic phase on the surface of a polyethersulfone microporous membrane. The attributes of SCNF, excellent hydrophilicity, and highly negative charges enhanced both the rejection and water permeability. As the SCNF charge increased, the roughness of SCNF increased and the contact angle decreased, and the maximum values were 203 nm and 17.67°, respectively. Among all the composite NF membranes, H-SCNF/Ag-0.01 had better rejection of Na2SO4 and NaCl, with a maximum rejection of 97.11% and 32.55%, respectively. Meanwhile, it also maintained high water permeability. Antibacterial experiments indicated that the composite NF membrane had effective inhibition against Escherichia coli and exhibited an expected slow-release capability of Ag+, which made it have long-term antibacterial properties. It was estimated that the antibacterial effect could last for 90 days. This work demonstrated that AgNPs in situ immobilization on SCNF could be used as promising nanofillers for designing advanced functional NF membranes.

High performance antibiofouling hollow fiber polyethersulfone nanocomposite membranes incorporated with novel surface-modified silver nanoparticles suitable for membrane bioreactor application

Surface-modified silver nanoparticles with amine, thiol, carboxyl, and the thiol-polyvinylpyrroldidone (PVP) functional groups were synthesized as functional filler for nanocomposite membranes for membrane bioreactor (MBR), with the aims to enhance antimicrobial effect of silver, while immobilizing silver nanoparticles inside the matrix of the membrane. Analyses by fourier transform infrared (FTIR), field emission scanning electron microscopy (FESEM), and dynamic light scattering (DLS) proved successful surface modification for each type of nanoparticles, with average particle sizes of 69, 20, 33, and 34 nm for amine, carboxyl, thiol and thiol-PVP modified silver nanoparticles, respectively. Polyethersulfone (PES) based nanocomposite hollow fiber membranes showed different morphology and performance in ultrafiltration and MBR experiments. The surface modifications were able to immobilize silver nanoparticles inside the membrane by providing proper interactions between the nanoparticles and polymer, reducing silver release compared to the unmodified nanoparticles. Modified nanoparticles changed the phase inversion, resulting in different morphology and average pore size in the range of 7.6–28.0 nm. The surface-modified nanoparticles with enhanced antimicrobial activity improved antifouling properties of the nanocomposite membranes, leading to interesting MBR performance improvements, with 122 % increase of flux, 23 % increase of chemical oxygen demand (COD) removal and flux recovery by over 30 %.

Detecting mercury ions in water using a low-cost colorimetric sensor derived from immobilized silver nanoparticles on a paper substrate

The exceptional and specific reactivity of mercury ions (Hg2+) toward plasmonic silver nanoparticles (AgNPs) in aqueous media has motivated the need to develop innovative, low-cost, portable, and robust sensors to help address the detrimental effects of heavy metal contamination particularly in rural communities. In this paper, we present the plasmonic and colorimetric sensing of Hg2+ using a paper-based sensing material derived from thiamine-functionalized (ThAgNPs) that were immobilized on a commercial filter paper. Plasmonic AgNPs with a surface plasmon resonance peak at 420 nm and a size of about 21.3 nm were synthesized by a chemical reduction technique. Fourier transform infrared spectroscopy revealed the characteristic functional groups of thiamine in the spectra of AgNPs, thereby confirming the functionalization of AgNPs. The successful integration of ThAgNPs onto the Whatman filter paper (WFP) matrix was confirmed by the UV–vis and SEM-EDX results. An evident color change from yellowish to white was manifested by the fabricated WFP-ThAgNP sensor in the presence of Hg2+ with an appreciable detection of up to 0.5 µM using the naked eye. The colorimetric response of the sensor was also found to be selective towards Hg2+ after testing with different metal ions. Moreover, the response was consistent for tap, and creek water samples spiked with Hg2+. The results of this work provide a promising baseline technology for the development of an affordable, fast, portable, and reliable sensor that can be used for on-site detection and monitoring of Hg2+ levels in the water.

A high-sensitivity thin-film MWNT@PDA-AgNP nanocomposite sensor for acquiring microscopic deformations

Carbon nanomaterial/polymer-based flexible strain sensors form the foundations of many cutting-edge applications, e.g., personalized health monitoring, human-machine interaction, etc. However, achieving a high sensitivity to slight deformations remains a challenging task for the existing technologies. Herein, we immobilize silver nanoparticles (AgNPs) onto the surfaces of multi-wall carbon nanotubes (MWNTs) by a polydopamine (PDA)-assisted process, in order to fabricate a new nanocomposite sensor for capturing microscopic static deformations (strain: <1%) and microscopic high-frequency vibrations (strain: <0.001%, frequency: up to 100 s kHz). The material characterizations performed show that AgNPs are compounded, in their elemental state, with the PDA nanolayers on the surfaces of MWNTs, and help to lower the potential barriers between nanofillers. As such, the tunneling of electrons across adjacent nanofillers, which underpins the sensing of slight deformations, is promoted. The proposed nanocomposite sensor demonstrates a significantly higher sensitivity to both static (gauge factor: ∼38) and dynamic deformations, than control specimens that are fabricated from pure MWNTs or PDA-coated MWNTs. Moreover, the sensitivity of the new sensor to microscopic high-frequency vibrations is positively related to the mass of the AgNPs added. This study presents a promising surface modification approach for optimizing the sensitivities of carbon nanomaterial/polymer-based strain sensors to slight deformations.

Highly sensitive sensing and quantitative detection of sulfate ion with a SERS chip-based on boric acid's Lewis effect.

Based on the Lewis acid's coordination principle, a surface-enhanced Raman scattering (SERS) chip strategy had been developed for the ultrasensitive quantitation of SO42-. Through the immobilization of silver nanoparticles (Ag NPs) and the construction of the boric acid-based sensing unit, the chip system displayed outstanding merits on the direct sensing of SO42-, e.g., simple operation, ultra-high sensitivity, reproducibility, excellent selectivity and specificity. Moreover, an accurate evaluation was obtained by ratiometric calculations on characteristic peaks (1382 and 1070cm-1) for quantitative detection of SO42-. The detection limit was down to 10nM. Tap water, beer, and mineral water samples were tested, and high recoveries were achieved (97.12-110.12%). Besides, such SERS chip also displayed strong applicability for the evaluation of SO32-. Therefore, this SERS chip provided a promising idea for the quantification of trace amounts of SO42- and SO32- in the fields of food safety and environmental monitoring.

Structural Evolution of Palygorskite as the Nanocarrier of Silver Nanoparticles for Improving Antibacterial Activity.

The carrier performance of palygorskite (Pal) can be significantly affected by its structure, morphology, and activity, which was regulated by controlling the dissolution degree of the metal-oxygen octahedron of raw Pal (RPal) under the action of oxalic acid (OA) in this study. The RPal and OA-leached RPal (OPal) then served as supports for immobilizing silver nanoparticles (AgNPs) to form RPal/AgNPs and OPal/AgNPs antibacterial nanocomposites. The structural and morphological characterizations were used to confirm the dispersion uniformity of AgNPs on the RPal and OPal nanorods, and antibacterial experiments were conducted to evaluate the performance of as-prepared composites and also investigate their antibacterial mechanism. The results showed that OPal-48h (OA leaching for 48 h) loaded with AgNPs (OPal-48h/AgNPs) possesses the most excellent and broad-spectrum antibacterial properties, where its minimum inhibitory concentration values against E. coli, S. aureus, ESBL-E. coli, and MRSA reached 0.25, 0.125, 0.25, and 0.5 mg/mL, respectively, which are mainly attributed to the optimal balance between surface activity and structural stability of OPal-48h that maximally increased its dispersibility and active sites, therefore contributing to the in situ formation of monodisperse AgNPs on the nanorods of OPal-48h.

AgNPs-thiols modified PVDF electrospun nanofiber membrane with a highly rough and pH-responsive surface for controllable oil/water separation

To develop a novel membrane with controllable wettability in response to external stimuli for intelligent oil/water separation is always in urgent demand. In this study, a pH-responsive nanofibrous membrane was prepared through the step-by-step modification of polyvinylidene fluoride (PVDF) electrospun nanofiber membrane, including mussel-inspired self-polymerization of polydopamine (PDA), immobilization of silver nanoparticles (AgNPs) and self-assembly of thiols. A rough membrane surface could be formed by the loading of AgNPs, and the subsequent introduction of HS(CH2)11CH3/HS(CH2)10COOH via metal-thiol coordination could endow the membrane with pH-responsive wettability. The surface of the membrane was able to quickly and reversely switch between superhydrophobicity and superhydrophilicity through simply applying pH stimulus at pH 7 and 13, respectively. The membrane can be applied for separating multiphase oil/water mixtures, achieving separation efficiency of over 99.2% for light oil/water mixture and 96.5% for heavy oil/water mixture with a stable flux of around 2500 L/m2·h for water and 11,000 L/m2·h for oil over the 10-cycle separation process. Meanwhile, the membrane exhibited separation efficiency of higher than 99% for all the tested oil-in-water emulsions, and the water flux of the membrane could be effectively recovered by water rinsing. Moreover, the membrane demonstrated a good structural stability against rigorous mechanical abrasion. The pH-responsive membrane could be potentially applied for smart and energy-saving separation and recycle of oil or water from oily wastewater.

Cotton fabric coated with graphene-based silver nanoparticles: synthesis, modification, and antibacterial activity

In this study, reduced graphene oxide with immobilized silver nanoparticles cotton fabric (Ag/rGO/cotton) was produced by the dip-coating cotton in silver immobilizing onto graphene oxide (Ag/GO) suspension to prepared Ag/GO/cotton material followed by the addition of vitamin C (VC) as an environmentally friendly reducing agent. The characteristics of Ag/GO and modified cotton were investigated by Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, transmission electron microscopy, scanning electron microscope, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectroscopy. Silver nanoparticles (AgNPs) were uniformly distributed on the surface of graphene oxide (GO) sheets with an average size of 10–15 nm, while the cotton surface was evenly covered by Ag/rGO. The zone of inhibition against Staphylococcus aureus (S. aureus), Pseudomonas aeruginosa (P. aeruginosa), and Escherichia coli (E. coli) bacteria indicated that Ag/rGO/cotton possessed the highest antibacterial activity when compared to other modified cotton. Moreover, the Ag/rGO/cotton also exhibited effective hydrophobicity with a wetting angle of 103.85° ± 0.75°, which supported the prevention of bacterial infection and adherent on the cotton surface. To confirm the low cytotoxic property of Ag/rGO/cotton for human use, the cell viability of HepG2, A549, and Hek293 cell lines were evaluated when contacted with the material, while the low amount of leached Ag+ from Ag/rGO/cotton was under the accepted limit. All results of the study confirmed that Ag/rGO/cotton possesses significant potential for several antibacterial applications such as protective equipment.Graphic abstract

Single-dip colorimetric detection of cyanide using paper-based analytic device based on immobilized silver nanoparticles

Single-dip colorimetric detection of cyanide using paper-based analytic device based on immobilized silver nanoparticles

Green Synthesis AgNPs Immobilized to Whatman Paper Using Chromolaena odorata Extract and Its Application as Photocatalyst

Synthesis and immobilization of silver nanoparticles (AgNPs) to Whatman paper carried out using Cromolaena odorata extract irradiated by sunlight. The UV-Vis shows silver nanoparticles successfully formed from AgNO3 1 mM, 2 mM, and 3 mM with the absorption peaks at 455 nm, 452 nm, and 451 nm, respectively. The SEM shows AgNPs are spherical with an average particle size are 60.45 nm, 63.19 nm, and 68.42 nm, respectively. The EDX spectrum shows the composition of silver immobilized to Whatman paper increase with increasing concentration of 10.14Wt%, 64.48Wt%, and 70.48 Wt%, respectively. AgNPs/Whatman paper has a cubic crystal structure, space group Fm-3m, lattice parameter (a) 4.0862 Ǻ and crystal size of 42.94 nm. FTIR reach peaks at 520.78 cm-1 and 1,059 cm-1 explains the vibration of the Ag-O bonds indicated the formation of AgNPs. Furthermore, the photocatalyst ability for dye degradation was evaluated using methylene blue 10 ppm under sunlight for 6 hours. The result shows a changed colour to fade and decreases the absorbance ability of methylene blue. Therefore, it can be concluded that green synthesis and immobilization of AgNPs/Whatman paper have a potential to be applied as photocatalyst materials for dye degradation.

Laser-Assisted Nanotexturing and Silver Immobilization on Titanium Implant Surfaces to Enhance Bone Cell Mineralization and Antimicrobial Properties.

Despite the great advancement and wide use of titanium (Ti) and Ti-based alloys in different orthopedic implants, device-related infections remain the major complication in modern orthopedic and trauma surgery. Most of these infections are often caused by both poor antibacterial and osteoinductive properties of the implant surface. Here, we have demonstrated a facile two-step laser nanotexturing and immobilization of silver onto the titanium implants to improve both cellular integration and antibacterial properties of Ti surfaces. The required threshold laser processing power for effective nanotexturing and osseointegration was systematically determined by the level of osteoblast cells mineralized on the laser nanotextured Ti (LN-Ti) surfaces using a neodymium-doped yttrium aluminum garnet laser (Nd:YAG, wavelength of 1.06 μm). Laser processing powers above 24 W resulted in the formation of hierarchical nanoporous structures (average pore 190 nm) on the Ti surface with a 2.5-fold increase in osseointegration as compared to the pristine Ti surface. Immobilization of silver nanoparticles onto the LN-Ti surface was conducted by dip coating in an aqueous silver ionic solution and subsequently converted to silver nanoparticles (AgNPs) by using a low power laser-assisted photocatalytic reduction process. Structural and surface morphology analysis via XRD and SEM revealed a uniform distribution of Ag and the formation of an AgTi-alloy interface on the Ti surface. The antibacterial efficacy of the LN-Ti with laser immobilized silver (LN-Ti/LI-Ag) was tested against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. The LN-Ti/LI-Ag surface was observed to have efficient and stable antimicrobial properties for over 6 days. In addition, it was found that the LN-Ti/LI-Ag maintained a cytocompatibility and bone cell mineralization property similar to the LN-Ti surface. The differential toxicity of the LN-Ti/LI-Ag between bacterial and cellular species qualifies this approach as a promising candidate for novel rapid surface modification of biomedical metal implants.

Silver nanoparticles decorated on graphene oxide modified polyester fabric: Catalytic reduction of 4-nitrophenol, organic dyes and SERS application

We report on the immobilization of silver nanoparticles on functional graphene oxide modified polyester fabric (AgNPs@GO/PET) for catalytic reduction of organic pollutants. In this work, the polyester fabric was modified with hydrophobic graphene nanosheets using a simple dip-coating method. The as prepared hydrophobic inert graphene oxide modified polyester fabric (GO/PET) substrate was used to stabilize oleylamine coated monodispersed silver nanoparticles. The morphology, size, and structure of the catalyst was investigated through X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), dynamic light scattering (DLS), Fourier-transform infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA) and Raman spectroscopy. Outstanding catalytic performance was exhibited by the AgNPs@GO/PET catalyst for the reduction reaction of 4-nitrophenol, methyl orange and methyl red. Surface enhanced Raman scattering (SERS) was also employed for the time dependent monitoring of reduction of 4-Nitrothiophenol. The present work highlights the importance of the as developed catalyst for the catalytic reduction of organic pollutants and SERS sensing with excellent stability and reusability.

Bi2MoO6 and Ag nanoparticles immobilized on textile by plasma-derived innovative techniques to generate antimicrobial activity

In this study, we expose various techniques based on cold plasma discharge (CPD), and more precisely aqueous-phase plasma-aided grafting (APPAG), to efficiently modify the surface of polymers as well as fabric made of natural fibers. Several directions were investigated to ultimately add a functional coating providing an antimicrobial effect to textiles. Our strategy relies on the immobilization of silver nanoparticles (AgNPs) and Bi2MoO6 (BMO) – a robust inorganic photocatalyst that can be activated by visible light – microflowers, at the surface of cotton fabric fibers. Notably, an in situ complexation-assisted precipitation route (ISCAP – an original method derived from CPD) was successfully employed to generate a very uniform coating of silver nanoparticles at the surface of organic substrates. As we demonstrate in this study, the surface functionalization with BMO and silver provides a significant protection against bacteria in dark conditions, through a bacteriostatic effect of nano silver, and under low-intensity artificial visible light (thanks to the photocatalytic effect of BMO/Ag), hence suitable for an indoor environment such as hospitals. Our composite nanomaterial, cotton/BMO/AgNPs, was assessed through antibacterial testing with Escherichia coli (E. coli) and Staphylococcus aureus (S. Aureus), showing a pronounced antimicrobial effect with both strains. This study opens prospects for the functionalization of natural or artificial fiber materials with possible applications in the field of biomedical protective equipment such as bandages, masks or technical cloths; or even photocatalysis.

High antibacterial activity of chitosan films with covalent organic frameworks immobilized silver nanoparticles

In this study, chitosan (CS) film containing covalent organic frameworks (COFs) immobilized silver nanoparticles (AgNPs) were developed for food packaging with improved antibacterial activities and film properties. COFs-AgNPs were fabricated via in-situ synthesis of immobilizing AgNPs on COFs. Transmission electron microscope, Zeta potential, X-ray diffraction, element mapping and Fourier transform infrared spectroscopy confirmed the successful fabrication of COFs-AgNPs, and COFs-AgNPs showed superior antibacterial activity against S. aureus and E. coli. Furthermore, the as-prepared COFs-AgNPs composite was further used to fabricate CS composite films (CS/COFs-AgNPs) by a solution casting method. The findings showed that the tensile strength of the nanocomposite films enhanced dramatically with the increase of the COFs-AgNPs content, while the UV–visible light barrier property, water swelling and solubility properties, and water vapor permeability (WVP) decreased significantly. Not only that, the CS/COFs-AgNPs nanocomposite films also showed outstanding antibacterial activity and effectively prolonged the storage time of white crucian carp (Carassius auratus). As a result, CS/COFs-AgNPs nanocomposite films show great potential in active food packaging.

Cellulose nanocrystals isolated from corn leaf: straightforward immobilization of silver nanoparticles as a reduction catalyst.

As the most abundant natural biopolymer on earth, celluloses have long-term emerged as a capable platform for diverse purposes. In the context of metal nanoparticles applied to catalysis, the alternatives to traditional catalyst supports by using biomass-derived renewable materials, likely nanocelluloses, have been paid a great effort, in spite of being less exploited. In this study, cellulose nanocrystals were isolated from corn leaf via chemical treatment involving alkalizing, bleaching and acid hydrolysis. The crystallinity of obtained cellulose was evaluated in each step, focusing on the effects of reactant concentration and reaction time. Cellulose nanocrystals were characterized by powder X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), evidencing the presence of cellulose nanospheres (crystallinity index of 67.3% in comparison with 38.4% from untreated raw material) in the size range of 50 nm. Without using any additional surfactants or stabilizers, silver nanoparticles (AgNPs) well-dispersed on the surface of cellulose nanocrystals (silver content of 5.1 wt%) could be obtained by a simple chemical reduction using NaBH4 at room temperature. The catalytic activity was evaluated in the selective reductions of 4-nitrophenol towards 4-aminophenol and methyl orange towards aromatic amine derivatives in water at room temperature. The effects of catalyst amount and reaction time were also studied in both reduction processes, showing near-quantitative conversions within 5 minutes and obeying the pseudo-first-order kinetics, with the apparent kinetic rate constants of 8.9 × 10-3 s-1 (4-nitrophenol) and 13.6 × 10-3 s-1 (methyl orange). The chemical structure of the catalytic system was found to be highly stable during reaction and no metal leaching was detected in reaction medium, evidencing adaptability of cellulose nanocrystals in immobilizing noble metal nanoparticles.

Benefits of Usage of Immobilized Silver Nanoparticles as Pseudomonas aeruginosa Antibiofilm Factors.

The aim of this study was to assess the beneficial inhibitory effect of silver nanoparticles immobilized on SiO2 or TiO2 on biofilm formation by Pseudomonas aeruginosa—one of the most dangerous pathogens isolated from urine and bronchoalveolar lavage fluid of patients hospitalized in intensive care units. Pure and silver doped nanoparticles of SiO2 and TiO2 were prepared using a novel modified sol-gel method. Ten clinical strains of P. aeruginosa and the reference PAO1 strain were used. The minimal inhibitory concentration (MIC) was determined by the broth microdilution method. The minimal biofilm inhibitory concentration (MBIC) and biofilm formation were assessed by colorimetric assay. Bacterial enumeration was used to assess the viability of bacteria in the biofilm. Silver nanoparticles immobilized on the SiO2 and TiO2 indicated high antibacterial efficacy against P. aeruginosa planktonic and biofilm cultures. TiO2/Ag0 showed a better bactericidal effect than SiO2/Ag0. Our results indicate that the inorganic compounds (SiO2, TiO2) after nanotechnological modification may be successfully used as antibacterial agents against multidrug-resistant P. aeruginosa strains.

Reductant free green synthesis of magnetically recyclable MnFe2O4@SiO2-Ag coreshell nanocatalyst for the direct reduction of organic dye pollutants.

The present paper describes in situ green immobilization of silver nanoparticles on MnFe2O4@SiO2 nanospheres using Epilobium parviflorum (EP) without using any other toxic chemicals and reducing or stabilizing agents. The morphology, composition, and magnetic properties of the resulting MnFe2O4@SiO2-Ag core-shell nanocatalyst were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). The catalytic performance of the synthesized MnFe2O4@SiO2-Ag was employed on the organic pollutants dyes such as rhodamine B (RhB) and methylene blue (MB). The results revealed significant reduction performances for the MB (116.28 s-1 g-1) and RhB (27.12 s-1 g-1) over the existing literature. Furthermore, the MnFe2O4@SiO2-Ag exhibited high stability for the completion of the reduction of RhB between the reaction times of 13.1 (first) and 19.8 min (final) with the 100% decolorization efficiency even after several cycles with an excellent magnetic separation. Overall, this work demonstrates a simple and practical green synthetic route for the preparation of magnetic recyclable core-shell nanocatalyst that can be a good candidate for the treatment of organic contaminants in wastewater adhering to green chemistry principles for the environmental pollution concerns.

Antibacterial and cytotoxic activity of metronidazole and levofloxacin composites with silver nanoparticle

Abstract The aim of the work is to to ascertain their antibacterial activity, as well as the toxic effects toward human cells of composites of silver nanoparticles immobilized by electron-beam technology onto crystals of antimicrobial agents metronidazole and levofloxacin The assessment of antibacterial activity and cytotoxic action of silver naonparticled metronidazole and levofloxacin composites was carried out using the MTT-test. Objects of study of antibacterial activity were three strains of microorganisms: Staphylococcus aureus ATCC25923, Escherichia coli dH5α, Pseudomonas aeruginosa ATCC9027. For the investigation of cytotoxic action, cells of HEK 293 line obtained from human kidney embryos were used. Nanocomposites of metronidazole and levofloxacin were tested at concentrations known as the minimum toxic dose of antibiotics and at concentrations reduced/increased in 2 times. Immobilization of silver nanoparticles on the surface of metronidazole and levofloxacin by electron-beam technology gives a different effect on their antibacterial and cytotoxic activity. Nanocomposites of metronidazole exhibit a weaker antibacterial effect on E. coli than metronidazole alone, while levofloxacin nanocomposites have higher antibacterial activity compared to levofloxacin alone. Nanocomposites of the levofloxacin, compared to free levofloxacin, are characterized by a higher antibacterial effect towards gram-negative bacteria (E. coli), but practically do not differ in activity toward P. aeruginosa and S. aureus. Immobilization of silver nanoparticles on metronidazole crystals does not affect on its cytotoxicity relative to pseudonormal human cells line HEK 293, while the nanocomposites of levofloxacin with silver are more toxic to these cells than levofloxacin alone.